Roman coloured glass in the Western provinces: The glass cakes and tesserae from West Clacton in England

Accepted Manuscript Roman coloured glass in the Western provinces: the glass cakes and tesserae from West Clacton in England Sarah Paynter, Thérèse Kearns, Hilary Cool, Simon Chenery PII:

S0305-4403(15)00228-9

DOI:

10.1016/j.jas.2015.07.006

Reference:

YJASC 4460

To appear in:

Journal of Archaeological Science

Received Date: 28 February 2015 Revised Date:

30 June 2015

Accepted Date: 7 July 2015

Please cite this article as: Paynter, S., Kearns, T., Cool, H., Chenery, S., Roman coloured glass in the Western provinces: the glass cakes and tesserae from West Clacton in England, Journal of Archaeological Science (2015), doi: 10.1016/j.jas.2015.07.006. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT 1

Roman coloured glass in the Western provinces: the glass cakes and tesserae from West Clacton

2

in England.

3 4

Sarah Paynter1, Thérèse Kearns2, Hilary Cool3 and Simon Chenery4

RI PT

5 1. Historic England, Fort Cumberland, Fort Cumberland Road, Eastney, Portsmouth, PO4 9LD

7

[email protected]

8

02392 856782

SC

6

9

2. Historic England, Fort Cumberland, Fort Cumberland Road, Eastney, Portsmouth, PO4 9LD

11

[email protected]

12

M AN U

10

13

3. Barbican Research Associates, 16 Lady Bay Rd, Nottingham, NGE 5BJ

14

[email protected]

TE D

15

4. British Geological Survey, Environmental Science Centre, Nicker Hill, Keyworth, Nottingham,

17

NG12 5GG

18

[email protected]

20

1. Introduction

AC C

19

EP

16

21

Scientific analysis has been used to great effect to study the production, trade and use of ancient glass

22

(Janssens 2013). For the Roman period, many analytical studies have concentrated on colourless or

23

naturally coloured blue-green glass, which make up the vast majority of assemblages (Jackson and

24

Paynter 2015; Jackson 2005; Foy et al. 2000a). For assemblages from Britain, there have been fewer

25

analyses of contemporary strongly coloured glass, which was used for enamelling and making items

26

of jewellery, gaming counters and tesserae, as well as certain glass vessels (Foster and Jackson 2005;

27

Henderson 1991). More work has been done on Roman coloured glass from further afield however,

ACCEPTED MANUSCRIPT particularly continental Europe and Egypt, and there are many studies of medieval assemblages that

29

may feature reused or recycled Roman glass (for example Galli et al. 2004, Gedzevičiūtė et al. 2009,

30

Nenna and Gratuze 2009, Silvestri et al. 2012, van der Werf et al. 2009). The compositions of

31

coloured glass are complex, as a range of elements can be introduced as part of the colourant,

32

intentionally or not. A number of distinctive compositional groups have now been identified,

33

depending on the colour and date of the glass (Henderson 1991); however there are still outstanding

34

questions about how coloured glass production was organised in the Roman period.

35

This paper sheds light on the subject of Roman coloured glass production by investigating two

36

fragments from rounded cakes of strongly coloured Roman glass and a selection from over 200 glass

37

tesserae that were excavated in 2007 at West Clacton Reservoir, Essex, in the UK, by Colchester

38

Archaeological Trust (Brooks and Holloway 2007; Cool 2007). The glass was found within a pit

39

where it had probably been deposited in a small textile or leather bag, and is likely to date from the

40

2nd century AD based on comparable finds from elsewhere in the UK. These include a collection of

41

over a thousand tesserae from London (A. Wardle pers. comm.) and others from Carlaeon

42

(Zienkiewicz 1993, 105–106) and Castleford (Cool and Price 1998, 193), all dominated by opaque

43

blue glass, coloured by cobalt oxide. At Romano-British sites in the UK, glass tesserae were

44

occasionally used for highlights in mosaics, which were otherwise made from stone, and also as

45

enamel for metal vessels or brooches (Cool 2007; Cool et al. 1995, 1592; Cool and Price 1998).

46

This collection included 201 cubic tesserae in thirteen different colours, with a further 25 triangular

47

fragments and flakes (Figure 1). The two cake fragments were both opaque blue; one turquoise and

48

the other a deep blue shade. Although incomplete, the shape of the surviving fragments indicates that

49

the cakes were originally several centimetres thick with smooth sides and upper surfaces, made from a

50

gather of coloured glass that cooled on a flat surface, rather than in a container (Figure 2). Whilst blue

51

glass is very common amongst tesserae assemblages from the UK, and also dominates this

52

assemblage, opaque turquoise is rare, making the turquoise cake a particularly significant find. Of the

53

tesserae and flakes, 107 were opaque dark to mid-blue, 39 were translucent dark to mid-blue (with

54

some transparent), 7 were opaque red, 25 opaque yellow, 15 opaque yellow-green, 4 opaque

AC C

EP

TE D

M AN U

SC

RI PT

28

ACCEPTED MANUSCRIPT 55

turquoise, 19 opaque pale grey-blue, 8 opaque green, 1 opaque emerald green and 1 translucent

56

emerald green.

57

2.

Background

59

2.1 Colourless and naturally coloured blue-green Roman glass

60

Most glass used in the Romano-British period, for tableware, bottles, and windows, was either

61

completely colourless or naturally coloured (i.e. with a weak blue-green or aqua hue). The bluish-

62

green tint was due to small amounts of iron oxide that were introduced unintentionally with the raw

63

materials. Studies of Roman colourless and naturally coloured (blue-green) glass have found that

64

there were relatively few different glass compositions in circulation during the 1st to 3rd centuries AD

65

(Jackson 2005; Nenna et al. 1997; Foy et al. 2000a and b). Decolourising compounds, such as

66

antimony or manganese oxide, were added in order to make completely colourless glass, which was

67

preferred for high status tableware. Mixed compositions were produced as a result of recycling the

68

manganese and antimony decolourised glass together (Jackson and Paynter 2015).

69

Large furnaces for primary glassmaking have been identified in the Wadi natrun area of Egypt dating

70

to this period (Picon et al. 2008) but it is very likely that there are others still to be found; later

71

examples are known from the Syro-Palestinian coast (Freestone et al. 2000). A fresh interpretation of

72

contemporary accounts of glass production, particularly the description by Pliny (Eichholz 1962), has

73

stemmed from these archaeological discoveries and analytical studies, in which a relatively small

74

number of primary manufacturing centres made raw glass on a large scale. Chunks of raw glass were

75

then transported to secondary workshops to be made into vessels (Foy et al. 2000a and 2000b), and

76

broken glass was also collected and used as cullet for recycling.

77

The glass was made using natron combined with sand (Sayre and Smith 1967), generally including

78

calcium carbonate from shells (Wedepohl and Baumann 2000). Natron glass is therefore a type of

79

soda-lime-silica glass, with characteristically low levels of potassium, magnesium and phosphorus

AC C

EP

TE D

M AN U

SC

RI PT

58

ACCEPTED MANUSCRIPT 80

oxides relative to Bronze Age glass for example, which was manufactured using plant ashes (Turner

81

1956). The types of natron glass in use around the 2nd century AD, contemporary with the West

82

Clacton assemblage, are dominated by a small number of compositional groups (Foy et al. 2000a and

83

b; Jackson 1994 and 2005; Jackson and Paynter 2015); in this paper these are referred to as:

lime relative to other types, with 0.6-1.5wt% manganese oxide acting as a decolouriser.

85 •

to lime, but with less than 0.6wt% manganese oxide.

87 88

•

Sb glass: Consistently colourless glass, which has a high ratio of soda to lime and varying amounts of antimony decolouriser.

89 90

Low-Mn glass: Blue-green glass, similar to high-Mn glass with a fairly low ratio of soda

•

SC

86

High-Mn glass: Colourless to blue-green glass, characterised by a low ratio of soda to

RI PT

•

M AN U

84

Mixed Sb-Mn glass: Colourless to blue-green glass, produced when different glass types

91

(mainly colourless Sb glass and high-Mn glass) were recycled together. It contains an

92

intermediate ratio of soda to lime and a mixture of both antimony and manganese

93

decolourisers.

The Mn-bearing glass types are in use prior to the Roman Conquest of Britain, and continue

95

throughout the period of interest here, whereas the Sb decolourised glass is found mainly from the

96

1st to 3rd centuries AD, becoming rare by the mid-4th century. The recycled Sb-Mn glass, which

97

is made from a mixture of the antimony and manganese types, follows approximately the same

98

chronological pattern, becoming rarer through the 4th century (Jackson and Paynter 2015).

EP

AC C

99

TE D

94

100

2.2 Strongly coloured Roman glass

101

The compounds responsible for the colour and opacity of strongly coloured Roman glass have been

102

established previously (for example Arletti et al. 2006; Henderson 1991; Gliozzo et al. 2012; van der

103

Werf et al. 2009) but it has proved more difficult to determine the form in which they were added, or

104

where the colourants came from (Mass et al. 2002; Rehren 2003). White calcium antimonate

105

compounds Ca2Sb2O7 or CaSb2O6 are found in white glass and also in opaque turquoise and opaque

ACCEPTED MANUSCRIPT blue glass in combination with copper or cobalt colourants respectively. Calcium antimonate

107

opacifiers have been recreated experimentally by adding antimony compounds such as stibnite

108

(antimony sulphide) or antimony oxide to replica soda-lime-silica glass (Foster and Jackson 2005),

109

causing calcium antimonate crystals to form in situ through reaction with calcium from the glass

110

itself. Alternatively Lahlil et al. (2010a and b) made calcium antimonate beforehand by reacting

111

calcium and antimony compounds together, and then added this material to a ready-made glass.

112

Many opaque glass colours spoil easily because the type, size and distribution of the opacifying

113

particles must be controlled to obtain the desired colour. For example the yellow opacifier lead

114

antimonate, used for opaque yellow and also in combination with copper oxide for some green

115

colours, will start dissolving when added to a natron glass, with white calcium antimonate

116

precipitating instead. This is demonstrated by white Roman cameo glass of the early Empire, which

117

often contains more of both lead and antimony than the yellow glass analysed here, but is nonetheless

118

white (Mass et al. 1998). To ensure a strong yellow colour, it was necessary for the glassworkers to

119

make the lead antimonate colourant beforehand (Shortland 2002; Lahlil et al. 2008), and then add it to

120

a base glass; using an excess of lead and limiting the duration and temperature of any subsequent

121

glassworking would have helped to preserve the colour. Uniform red glass is also difficult to make

122

and shape (Freestone et al. 2003, Stapleton et al. 1999) as it is coloured by crystals of cuprite (Cu2O)

123

and metallic copper, formed under reducing conditions. During heating and working of the glass the

124

size of the crystals may change, or the glass can oxidise and the copper-rich crystals dissolve, both of

125

which alter the colour and opacity of the glass considerably.

126

AC C

EP

TE D

M AN U

SC

RI PT

106

127

3.

Aims

128

This study considers the types of colourant, opacifier and base glass that were used to produce

129

strongly coloured Roman glass, and how they interacted with each other, to explain differences in the

130

form of the opacifier found in particular glass colours. Factors such as the method of preparing the

131

opacifier, or the subsequent heat treatment of the glass, have been considered previously in explaining

ACCEPTED MANUSCRIPT these differences (for example Lahlil et al. 2008) but it is likely that the base glass composition also

133

plays an important role. This study combines ICP-MS macroscopic analysis of the glass, to obtain

134

more detailed information about the chemical composition of the colourant and opacifier materials,

135

with microscopic SEM-EDS examination, which reveals how these materials have interacted with the

136

glass. The aims of this approach are:

RI PT

132

137

•

To determine whether particular base glass types were preferred for certain colours.

138

•

To discuss how the composition of the base glass used may have affected the quality and

To ultimately establish a larger dataset for Roman coloured glass, with trace elements, for

M AN U

•

140

SC

stability of the colour produced and the type of opacifying crystals formed.

139

investigating regional and chronological variations.

141

142

4.

Methods

144

4.1 SEM-EDS

145

34 small samples were removed from the tesserae and cakes, mounted in epoxy resin and polished to

146

a 1µm finish for examination using an FEI-Inspect scanning electron microscope (SEM) with an

147

attached energy dispersive spectrometer (EDS) (19 of these samples were also analysed by ICP-MS).

148

The SEM conditions were an electron beam current of approximately 1nA and a voltage of 25 kV.

149

The EDS data was quantified using Oxford Instruments INCA software. The accuracy and precision

150

of the results was checked by analysing Corning and NIST glass standards (see Table 1). The SEM-

151

EDS data have been used for the major and minor elements in this paper, as the accuracy was better

152

than for the ICP-MS analyses. Averages of the results are given in Table 2 and the full dataset in

153

Appendix A. These are bulk analyses of random areas of approximately 0.08mm2 of each sample,

154

incorporating inclusions as well as the glass matrix in each case. A minimum of three analyses were

155

completed for each sample in order to obtain a more representative result because the tesserae were

156

heterogeneous, but larger samples were often analysed additional times. Crystalline phases and

AC C

EP

TE D

143

ACCEPTED MANUSCRIPT 157

inclusions were identified using point analyses to determine the composition; for example Ca2Sb2O7

158

and CaSb2O6 were differentiated based on the proportions of calcium and antimony oxides in each.

159

4.2 ICP-MS

161

24 glass samples were analysed by ICP-MS, with all but five of these also analysed using SEM-EDS.

162

The samples were powdered and 0.25g of each was digested using a mixed acid attack of 2ml

163

concentrated HNO3 acid followed by 2.5ml concentrated HF acid and 1ml concentrated HClO4 acid.

164

The samples underwent a heating cycle, using a programmable hot block, to reach incipient dryness.

165

When cool, 2.5ml of 50% v/v HNO3 acid was added and then 2.5ml concentrated H2O2, with each

166

addition followed by a brief period of further warming. The resultant solution was transferred to

167

LDPE storage bottles. 20ml of MQ quality water was used to rinse the original vials and added to the

168

LDPE bottles to give a volume of 25ml.

169

The determination of major and trace elements in stream waters was carried out using an Agilent

170

7500cx series quadrupole inductively coupled plasma mass spectrometer (ICP-MS) with an octopole

171

reaction system (ORS), in combination with a CETAC autosampler. The system was controlled by

172

through dedicated software (Agilent 7500 ICP-MS Chemstation B.03.06 (U300-0132)), which also

173

controlled the autosampler. A total acquisition time of 241s and a dwell time of 0.3ms were used.

174

The instrument was calibrated at the beginning of every analytical run using at least three standards

175

and a blank for each trace element and three standards and a blank for major elements. Multi-element

176

quality control standards, containing the trace elements of interest at 25µg l-1 and a separate major

177

elements quality control standard at varying element concentrations were analysed at the start and end

178

of each run and after no more than every 25 samples. These data were compared to fixed limits but

179

also charted and regularly reviewed. Each analytical run was independently verified by a different

180

analyst, including post processing of the data for drift, dilution and collation. Glass standards of

181

known composition were included in each run.

AC C

EP

TE D

M AN U

SC

RI PT

160

ACCEPTED MANUSCRIPT Detection limits were calculated as three times the standard deviation of the 1% nitric plus 0.5%

183

hydrochloric acid blanks inserted at regular intervals during the analysis. The uncertainty associated

184

with most ICP-MS measurements was ±10%. However, for, Na, Ca, Si, P, S, K, Fe, Zn, Sr and Ba,

185

the overall uncertainty is of the order of ±15% and for Li, B and Al the overall uncertainty is of the

186

order of ±20%. For quality control purposes each batch of samples typically contained 10% blanks,

187

10% reference materials and 10% duplicate samples if available. These were prepared and analysed

188

together with the rest of the glass samples. In this paper, the ICP data are used for the trace elements

189

and some minor elements, as the detection limits were better than for the SEM-EDS analyses (Table

190

1). The analytical data are shown in Appendix B.

SC

M AN U

191

RI PT

182

4.3 Comparability of SEM-EDS and ICP results

193

The results for standards with known compositions are given in Table 1. Although the antimony oxide

194

value for the ICP-MS analysis of the Corning D standard is anomalous, a comparison of the ICP-MS

195

and SEM-EDS results for the other standards, and for samples analysed by both techniques shows that

196

otherwise there is a consistent correlation in nearly all cases; Figures 3a, b and c show this correlation

197

for lead oxide, antimony oxide and copper oxide. Where there is a discrepancy between the SEM-

198

EDS and ICP-MS results, the sample in question is visually heterogeneous (for example the lead

199

content of two of the lead antimonate opacified yellow-green tesserae and the antimony content of one

200

turquoise and one mid-blue tesserae). These results are therefore likely to reflect real discrepancies

201

between the compositions of different parts of the same tesserae, with the part analysed by ICP-MS

202

containing a slightly different proportion of opacifier to the part analysed by SEM-EDS.

EP

AC C

203

TE D

192

204

4.4 Comparing the compositions of coloured glass against colourless and naturally coloured base

205

glasses

ACCEPTED MANUSCRIPT One of the aims of this investigation was to determine the type of base glass used to make the West

207

Clacton tesserae and cakes of coloured glass. To do this, the reduced composition of each glass was

208

calculated (Brill 1999), which could then be compared against literature data (Jackson and Paynter

209

2015) for contemporary colourless and naturally coloured (blue-green) Roman glass, which accounts

210

for the vast majority of Roman glass assemblages (Section 2.1). Compositional data were also

211

compared on graphs, but the presence of colourants and opacifiers in the coloured glass dilutes the

212

concentrations of the other compounds present, sometimes considerably. This affect can be negated

213

by plotting ratios of oxides or elements, preferably avoiding any that may have been introduced with

214

the colourants, opacifiers or decolourisers, whether intentionally or not. Different combinations of

215

element ratios were tested to ensure that the same base glass type was consistently identified in each

216

case, and one example is shown in Figure 4.

217

This process of identifying the probable base glass used for each sample was complicated by the fact

218

that compounds such as antimony, manganese and iron oxides are present in varying amounts in the

219

relevant base glass types as well as being common constituents of colourants and opacifiers. In

220

addition, calcium opacifiers could potentially have been added ready formed, thereby adding extra

221

calcium oxide, or additional flux could have been used to prepare colourants, thereby adding extra

222

sodium oxide, and so on. To allow for any of these possibilities, more than one characteristic was

223

used to identify the base glass composition in each case. The ratio of sodium to calcium oxides was

224

used as the first indicator of the likely base glass composition, with the ratio highest for colourless Sb

225

glass, lowest for the Mn family of glasses and intermediate for the mixed Sb-Mn glass (see Figure 4

226

for the spread of Na2O/CaO ratios). Other key characteristics of the glass were then checked, for

227

example the levels of phosphorus oxide and aluminium oxide tend to be lowest in colourless Sb-glass

228

and highest in the Mn-glass types (Figure 4). Finally the amounts of manganese present were

229

compared, as colourless Sb-glass does not contain any whereas mixed Sb-Mn glass contains

230

intermediate amounts; the manganese content is also indicated on Figure 4 by the fill of each

231

datapoint.

232

AC C

EP

TE D

M AN U

SC

RI PT

206

ACCEPTED MANUSCRIPT 5.

Results

234

15 samples (red: 20, 23, 25; emerald green: 17; blue: 82, 108, 147, 181; grey-blue: 65, 67; yellow: 61;

235

green-yellow: 9, 11; turquoise: 13; transparent blue: 70) were analysed only by SEM-EDS, five

236

samples (red: 21; green: 10, blue: 66; turquoise: 15; transparent blue: 19) only by ICP-MS and 19

237

samples (emerald green: 18; green: 3, 6; blue: cake, 74, 78, 88, 102,166, 176, 179; grey-blue: 69,

238

yellow: 51, 62, 64; yellow-green: 30, 35; turquoise: cake, 12) using both techniques. The

239

compositions of the analysed glass cakes and tesserae are given in Appendices 1 and 2.

240

These coloured glasses are soda-lime-silica types and although some contain high levels of lead oxide,

241

for example the yellow and red tesserae, it is well established that the lead was added as a constituent

242

of these colourants (Henderson 1991; Mass et al. 1998). The majority of colours were made using

243

Roman natron glass as a base, with characteristically low levels of potassium, magnesium and

244

phosphorus oxides (see Figure 5); the exceptions are some of the green tesserae and the opaque red

245

tesserae, which are discussed in more detail in Section 6.2.

M AN U

SC

RI PT

233

TE D

246

5.1 Base glass

248

Each of the calculated base glass compositions for most of the tesserae and both cakes were found to

249

approximately match one of the dominant categories of colourless and naturally coloured glass in

250

circulation in the 1st to 3rd centuries AD: Sb colourless, low-Mn, high-Mn or Sb-Mn mixed (Table 2)

251

(Figure 4). The West Clacton coloured glass was therefore made by adding colourants to types of base

252

glass that would have been widely available as raw glass chunks (Foy et al. 2000b) or cullet (Jackson

253

and Paynter 2015; Silvestri et al. 2008), both of which are found in glass workshops and ship wrecks

254

of the period.

255

Figure 4 shows that the cobalt-coloured mid-blue glass cake and tesserae, some of the pale grey-blue

256

tesserae and the majority of the analysed yellow-green tesserae, were made by adding colourants to

257

Mn glass (bottom left of Figure 4). The low-Mn and high-Mn glass types are compositionally similar

AC C

EP

247

ACCEPTED MANUSCRIPT with the exception of the manganese content, which influences whether the glass is colourless or has a

259

blue-green tint; this family of Mn compositions are thought to have been produced by long-lived and

260

large scale manufacturing centres on the Syro-Palestinian coast but were circulated over a wide area

261

(Foy et al. 2000a and 2000b). These Mn glass types are not particularly common in Roman Britain in

262

the 2nd and 3rd centuries; instead recycled Sb-Mn glass was often used for blue-green vessels

263

whereas Sb colourless glass was used for high status colourless tablewares (Jackson and Paynter

264

2015).

265

All of the copper-coloured turquoise glass, including the turquoise cake and three turquoise tesserae

266

were probably made using recycled Sb-Mn glass as a base. Some of the pale grey-blue tesserae, and

267

yellow-green tessera, may also be made from recycled Sb-Mn base glass.

268

Two cobalt-coloured transparent blue chips, which were visually distinctive, were both made from Sb

269

colourless glass of the type used for high quality tableware (Jackson 2005; Paynter 2006) to which a

270

cobalt colourant was added, but no opacifier. These tesserae may have been cut from a recycled

271

translucent blue vessel (Cool 2007) and plot at the top right of Figure 4.

SC

M AN U

TE D

272

RI PT

258

5.2 Colourant and opacifier reactions

274

A complex range of phases were observed in many of the samples, including dissolving raw materials,

275

transitional reaction products and precipitated crystals; there were also immiscible residues, rich in

276

sodium, chlorine or sulphur, trapped in the glass. The colourants used were typical of the Roman

277

period (Lahlil et al. 2008; 2010a and b; van der Werf et al. 2009; Henderson 1991).

278

Cobalt oxide was responsible for the deep to mid-blue colour of one of the cakes and large numbers of

279

tesserae (Table 2), with varying amounts of small, dispersed, euhedral crystals of calcium antimonate

280

(Ca2Sb2O7) also present in the glass (identified by SEM-EDS spot analyses). All of the analysed blue

281

opaque tesserae, ranging from dark blue to mid-blue, had been cut from the blue cake of glass; their

282

common origins are indicated by the consistent correlations between the colourant and opacifier

AC C

EP

273

ACCEPTED MANUSCRIPT oxides (cobalt and antimony) and associated elements (iron, manganese, nickel and lead) (Figures 6a

284

and 6b). There were also occasional larger crystals in these samples, which were again Ca2Sb2O7 but

285

contained variable amounts of substituted cobalt, iron and manganese, and also some clusters of a

286

different form of calcium antimonate (CaSb2O6), both of which appeared to be remnants from the

287

reaction of colourant minerals with the base glass. The strong correlation observed between the

288

concentrations of lead, copper, cobalt, nickel, arsenic and antimony in the bulk compositions of these

289

tesserae and the cake suggest that the added colourant contained all of these elements, as well as iron

290

and manganese (Figures 6a and 6b). Henderson (1991) also noted the correlated concentrations of iron

291

and manganese oxides in cobalt coloured late Iron Age and Roman enamel, and identified two

292

variants, one containing several weight percent lead oxide and the other containing very little,

293

although the source of cobalt appears unchanged. Together these observations suggest that cobalt and

294

antimony compounds (with associated gangue), from different sources, were combined in a

295

concentrated form in advance of adding them to the glass, and that the lead may have been introduced

296

with the antimony source. The colourant had been stirred in but it had not reached an even dilution

297

throughout, and so the concentrations and depth of colour varied between these samples.

298

Cobalt oxide was also responsible for the colour of the pale grey-blue tesserae but, relative to the cake

299

and darker blue tesserae, these contained a far higher ratio of antimony to cobalt and very little lead

300

(Figures 6a and 6b). There were at least two sources of pale grey-blue tesserae represented amongst

301

the samples selected for analysis because two different compositions of base glass had been used.

302

Finally the transparent deep blue chips were also coloured by cobalt oxide, but all of the antimony

303

oxide in these samples was in solution.

304

Copper oxide was responsible for the colour of the turquoise coloured tesserae and cake, together with

305

calcium antimonate opacifiers. Although several of the analysed turquoise tesserae had been cut from

306

the turquoise cake, indicated by their very similar compositions (13 and 15), others had not, for

307

example sample 12 contained significantly more copper oxide and was also a slightly different shape

308

and colour. As well as numerous small crystals of CaSb2O6 in the turquoise glass, identified by SEM-

AC C

EP

TE D

M AN U

SC

RI PT

283

ACCEPTED MANUSCRIPT EDS spot analyses, there were also occasional larger crystals of alkali antimonate (Na,K)SbO3 with

310

small amounts of substituted tin and calcium (Figure 7). These alkali antimonates again appear to be

311

the remnants of reactions between the colourants / opacifiers with the base glass. Previously these

312

were thought to indicate that alkalis were added to antimony compounds when the opacifier was

313

prepared (Paynter and Kearns 2011) but more detailed examination suggests that the crystals are

314

incorporating sodium and potassium from the melt. In the case of potassium, the resulting crystalline

315

phases contain several percent more potassium than found in the glass overall; the presence of tin

316

appears to favour the formation of these crystals. The concentrations of copper, tin and also antimony

317

in the glass are broadly correlated, again suggesting that these elements were introduced together, for

318

example using oxidised copper alloy as suggested in many previous studies (for example Frerickx et

319

al. 2004).

320

The yellow glass was produced using lead antimonate, crystals of which were identified throughout

321

the tesserae by SEM-EDS point analyses. The yellow tesserae also contained dissolving particles

322

comprising feldspar and iron-rich minerals (Figure 8), together with sulphide droplets and an

323

associated sodium alumina sulphate reaction product, nosean (Na8[Al6Si6O24]SO4) (Paynter and

324

Kearns 2011). The presence of these phases suggests that sulphide ores of lead or antimony were used

325

to make the colourant. The dissolving aluminium silicate particles may derive from ceramic crucibles

326

used to heat these compounds; the lead-rich crucible contents would react with the ceramic to produce

327

a glass in which yellow lead antimonate crystals precipitated (see for example Heck et al. (2003) for

328

the reactions of crucibles used in the preparation of lead stannate colourants). Elevated levels of tin

329

and iron oxides were detected in several samples, as also noted by Lahlil et al. (2008). A small droplet

330

containing silver was identified in one yellow tessera, which is consistent with a statement by Pliny

331

(NH XXXIII), that antimony ores were obtained from a mine exploited for its silver (Eichholz 1962).

332

Similarly many of the green tesserae were coloured by lead antimonate, but in combination with

333

copper oxide. A few of the green tesserae had been coloured differently however, for example sample

334

18 contained in excess of 2wt% iron oxide plus some partially dissolved particles of iron oxide,

335

indicating that iron oxide had been intentionally added as a colourant. There was also a subset of

AC C

EP

TE D

M AN U

SC

RI PT

309

ACCEPTED MANUSCRIPT green samples, which were again coloured by copper oxide but contained varying amounts of a plant

337

ash component resulting in elevated levels of potassium, magnesium and phosphorus oxides (Figure

338

5); these are similar to the distinctive emerald green glass identified in contemporary monochrome

339

Roman vessels (Henderson 1996; Jackson and Cottam 2015; Lemke 1998) and also in polychrome

340

vessels and mosaic glass (Nenna and Gratuze 2009; Paynter and Schibille forthcoming), which are

341

discussed in more detail in Section 6.2.

342

The red tesserae contained high levels of lead and copper oxides, again with a plant ash component,

343

indicated by elevated levels of potassium, magnesium and phosphorus oxides (Figure 5), and were

344

coloured by metallic copper or cuprite; similar compositions have been reported in studies of Roman

345

enamel and other tesserae (Di Bella et al. 2014; Henderson 1991), as well as monochrome and

346

polychrome vessels (Nenna and Gratuze 2009; Paynter and Schibille forthcoming). The levels of lead

347

oxide varied amongst the red tesserae, and so again these appear to be from more than one source;

348

those with higher lead are glossy and those with lower levels more matt and vesicular. In each case,

349

correlations were noted between the active colourant compounds and the concentrations of some other

350

compounds present, such as tin oxide, indicating that they were added to the glass together, albeit not

351

necessarily intentionally; similar correlations have been noted in tesserae from elsewhere (for

352

example Lahlil et al. 2008; Di Bella et al. 2014). The red tesserae also contained clusters of calcium

353

tin magnesium silicates, and calcium tin silicates (identified by SEM-EDS spot analyses) formed from

354

the interaction of the glass with the added colourant. The colourant is therefore likely to have

355

contained tin and calcium in addition to the lead and copper compounds. A red slag containing these

356

characteristic components was produced as a by-product from the contemporary process of refining

357

debased silver alloys; the possibility of this slag being used as a colourant in red glass production is

358

explored further in section 6.2. The red tesserae also contained complex dissolving particles, made up

359

of grains of feldspar, quartz and iron minerals, which might be remnants from the crucibles in which

360

the red slag colourant formed.

361

6.

AC C

EP

TE D

M AN U

SC

RI PT

336

Discussion

ACCEPTED MANUSCRIPT There are many available analyses of Byzantine and medieval tesserae, for which Roman material was

363

often reused or recycled. However several additional base glass compositions were introduced around

364

the 4th century AD (Jackson and Paynter 2015), which were then used in coloured glass production

365

(see for example Silvestri et al. 2012) and a number of different opacifiers were also adopted. These

366

complicating factors make comparison of later assemblages with the West Clacton tesserae more

367

complex and less informative. Therefore this section focuses on comparing the tesserae from West

368

Clacton to other published analyses for Roman coloured glass.

SC

369

RI PT

362

6.1 The choice of natron base glass

371

The type of base glass used to make opaque coloured glass varies chronologically reflecting what was

372

available at the time. For example, compositional data for strongly coloured Hellenistic or Late Iron

373

Age glass and glass of the early Empire are often consistent with the use of Mn-glass as a base, which

374

contains a lower ratio of sodium to calcium oxides plus some manganese (see the polychrome

375

Hellenistic glass in Gedzevičiūtė et al. 2009). Mn-glass continued to be used as a base for much

376

subsequent strongly coloured opaque glass, but from the mid-1st century AD a broader range of

377

natron glass types were available to use as a base, so which factors dictated the type of glass chosen to

378

make a particular colour? The availability and cost of the different glass types may have been

379

influential; the Mn-glass types in particular were produced and traded on a vast scale in this period,

380

and were widely available around the Mediterranean and in continental Europe (Foy et al. 2000b;

381

Jackson and Paynter 2015; Barag 1987). Recycled Sb-Mn glass was also used for high volume, lower

382

value items, like windows and bottles. In contrast the colourless Sb glass was reserved for high status

383

tableware. The specialists making strongly coloured glass may have simply used the most readily

384

available and least costly glass types as a base, since the Mn-glass and Sb-Mn glass appear to account

385

for most samples.

386

A second factor however, is that the calcium-rich composition of the Mn glass types was well suited

387

to producing opaque glass because calcium was conducive to the formation of the calcium antimonate

AC C

EP

TE D

M AN U

370

ACCEPTED MANUSCRIPT opacifier. The Mn family of glasses contain the highest proportion of calcium of any Roman glass,

389

therefore appear to require less antimony oxide to produce the desired opacification (0-2wt%),

390

making them intrinsically suitable for producing opaque glass. In contrast the colourless Sb-glass can

391

dissolve high concentrations of antimony oxide; some high quality colourless tableware contains in

392

excess of 3wt% (Paynter 2006), so may have been less suitable for making opaque strongly coloured

393

glass and seems to have been rarely used for that purpose. The only samples in this assemblage made

394

with colourless Sb-glass as a base were probably broken from a transparent cobalt blue vessel, and

395

were never intended to be fully opaque.

396

The intermediate Sb-Mn recycled glass composition was used as a base to make some of the opaque

397

glass in the West Clacton assemblage however, including all of the turquoise glass and possibly some

398

pale grey-blue and yellow samples. Potentially Sb-Mn glass may also have been used to make deep to

399

mid-blue opaque glass but, since all of the tesserae analysed from the West Clacton assemblage were

400

cut from the associated cake, this can’t be ascertained. The turquoise and pale grey-blue samples

401

made from an Sb-Mn base glass contain atypically high levels of antimony oxide overall (2-4wt%),

402

which will include the antimony that was originally dissolved in the base glass. The antimonate

403

crystals that have precipitated in the turquoise glass are forms containing less calcium, such as

404

CaSb2O6 instead of Ca2Sb2O7, as well as alkali antimonates and alkali antimony silicates. The high

405

ratio of sodium to calcium oxides in the melt appears to influence the type of opacifier that

406

precipitates, and also increases the solubility of these phases at a given temperature, so that distinct

407

euhedral crystals are less likely to form or persist as the melt homogenises. These glasses also tend to

408

contain more immiscible phases suggesting that the glassworking was minimised once the colourants

409

were added, perhaps to avoid further dissolving the opacifier.

410

A review of literature data suggests that turquoise tesserae were often made with an Sb-Mn base glass,

411

and possibly sometimes a colourless Sb-glass, indicated by a higher ratio of sodium to calcium oxides

412

and low levels of manganese oxide detected. The consistent use of the more sodium-rich base glass

413

types for this particular colour implies a deliberate choice. Examples are given by Lahlil et al. (2008),

414

who also observes the substitution of alkalis in the opacifiers in Roman turquoise tesserae; and

AC C

EP

TE D

M AN U

SC

RI PT

388

ACCEPTED MANUSCRIPT Henderson (1991), where a higher ratio of sodium to calcium oxides (and less manganese oxide) was

416

detected in Roman turquoise brooch enamel relative to cobalt blue or white enamel. Since Ca2Sb2O7 is

417

reported as the dominant phase in most coloured opaque Roman glass, a number of authors have

418

noted when CaSb2O6 is present instead, which is generally in turquoise glass. Di Bella et al. (2014)

419

detected CaSb2O6 as the dominant phase in turquoise tesserae from Sicily dating to the late 3rd or

420

early 4th centuries AD (see also Brun et al. (1989)). Silvestri et al. (2012) observed CaSb2O6 in

421

Roman pale blue, copper oxide coloured tesserae from Italy; Gliozzo et al. (2012) report other

422

examples, also from Italy. In addition some of the 3rd-century blue tesserae analysed by Ricciardia et

423

al. (2009) were coloured by copper oxide and contained high ratios of sodium to calcium oxides and

424

very little manganese oxide.

425

One influential factor may be that the type of base glass used had a noticeable effect on the final

426

colour of the copper oxide. This is demonstrated by the greener hue of the plant ash type copper oxide

427

coloured tesserae amongst the West Clacton assemblage, because the colour produced is influenced

428

by the concentrations of other compounds in the glass, such as the oxides of iron, manganese and

429

magnesium. High concentrations of alkalis and lower working temperatures are reported to produce

430

bluer (as opposed to green) hues in glasses and glazes coloured by copper oxide (Weyl 1953; Jackson

431

and Cottam 2015). Therefore Sb-glass and recycled Sb-Mn glass may have been selected because

432

their composition, with a higher concentration of sodium oxide and lower levels of manganese oxide,

433

ensured a brighter turquoise hue.

SC

M AN U

TE D

EP

AC C

434

RI PT

415

435

6.2 Green and red glass

436

The colourant used to make the West Clacton opaque red glass contained high levels of lead but, if

437

this is subtracted, the reduced composition is similar to the emerald green glass containing elevated

438

levels of potassium, magnesium and phosphorus oxides (Figure 5), which are indicative of a

439

contribution from plant ash (Turner 1956). Although soda-rich plant ashes were often used for glass

440

production in the past (Mirti et al. 2008; Sayre and Smith 1967), Roman red and green glass (Jackson

ACCEPTED MANUSCRIPT et al. 2009), as well as some other colours, such as black (Cagno et al. 2014) are distinctive, and

442

contain considerably more phosphorus oxide and a higher ratio of soda to potassium and magnesium

443

oxides than typical plant ash glasses (Jackson and Cottam 2015; Henderson 1996; Lemke 1998). The

444

first observation suggests that a different type of plant ash was used in the production of these colours

445

whereas the second may indicate that the glass also contains a natron component. The reasons for

446

including plant ashes are unclear but fresh plant ash glass has been shown to play an important role in

447

the production of medieval red glass because remnants of carbonaceous matter help to maintain

448

reducing conditions (Kunicki-Goldfinger et al. 2014). Figure 5 illustrates the elevated levels of

449

potassium and magnesium oxides in the base glass compositions of the red, and some green, tesserae

450

relative to the other colours from West Clacton; contemporary emerald green vessel glass or red glass

451

also contains elevated levels of these oxides (Henderson 1996; Lemke 1998; Paynter and Schibille

452

forthcoming).

453

Although lumps and strips of red glass have been found elsewhere in the UK (Bayley 2001 and 2005)

454

these are compositionally similar to earlier types of red glass dating to the Iron Age (Henderson 1991,

455

type 1), which contain considerably more lead oxide than the West Clacton red tesserae. The lower

456

lead composition of the West Clacton red glass (Henderson 1991, type 2) is typical for the Romano-

457

British period and consistent with the suspected 2nd century AD date of the assemblage. The very

458

lead-rich red glass typical of the British Iron Age, mentioned above (Henderson 1991), is reused red

459

slag from silver refining (Stapleton et al. 1999). Red slag was produced during certain stages of silver

460

refining in the Roman period and could potentially have been used as a colourant to make opaque red

461

glass (Mass et al. 1998); the composition of the slag differed depending on the type of alloy being

462

refined, the composition of the hearth used and any additional fluxes added. Analysed samples of

463

silver refining slag from Roman Xanten contained high concentrations of lead, copper and calcium

464

oxides with elevated tin and zinc oxides (Rehren and Kraus 1999), consistent with the traits identified

465

for the red tesserae analysed here. Red glass, matching the West Clacton composition, could be

466

produced by adding red slag from silver refining to a plant ash type base glass, similar to that used for

467

emerald green vessel glass, in a ratio of about 1:4 (slag to glass) by weight. Experimental work

AC C

EP

TE D

M AN U

SC

RI PT

441

ACCEPTED MANUSCRIPT 468

(Roman glassmakers 2002) has demonstrated the benefits of preparing a red colourant first, then

469

adding it to the glass, rather than trying to produce the red colour in situ (Kunicki-Goldfinger et al.

470

2014).

RI PT

471

7.

Conclusions

473

The glassworkers making this strongly coloured glass generally made use of existing supplies of

474

transparent natron glass, predominantly the naturally coloured (blue green) types, to which they added

475

the required colourants and opacifiers. Whilst there is documentary and archaeological evidence for

476

the production of Roman colourless and naturally coloured glass (Picon et al. 2008; Eichholz 1962),

477

mainly in the Eastern Mediterranean near to the required raw materials, there is little to suggest where

478

strongly coloured glass was made. The small size of the cakes of coloured glass produced for trade,

479

and the less frequent occurrence of strong colours in glass assemblages (Price and Cottam 1998), both

480

suggest that coloured glass was made and used on a much smaller scale than either colourless or

481

naturally coloured glass, potentially at specialist workshops. The ability of a workshop to produce

482

strongly coloured glass was dependent on whether the glassworkers had the necessary expertise, and

483

access to the raw materials required to make the colourants and opacifiers; sources of glass to use as a

484

base would have been easily obtained in comparison. Although copper and lead would have been

485

plentiful, antimony and cobalt minerals were more limited. For many colours, such as yellow and

486

probably red, the colourant was prepared first, and then added to the base glass. The opacifiers were

487

varyingly soluble in the glass, and the glass would have been worked as little as possible to preserve

488

the colour.

489

This study has highlighted differences in the types of glass used as a base for particular colours and

490

also the variable crystalline form of the opacifiers resulting in each case. Although different forms of

491

calcium antimonate opacifer have been identified previously in turquoise glass, the ratio of sodium to

492

calcium oxides in the base glass has not previously been considered as an important factor. The high

493

concentrations of calcium oxide in the manganese bearing glass types (high-Mn and low-Mn), and

AC C

EP

TE D

M AN U

SC

472

ACCEPTED MANUSCRIPT their widespread availability in the period of interest, made them intrinsically suitable for producing

495

calcium antimonate opacified colours. In contrast the high ratio of sodium to calcium oxides in the

496

antimony colourless (Sb) glass made it less suitable for opaque colours, although it was used to

497

striking effect to produce brilliant transparent cobalt blue vessel glass, some of which was reused to

498

make tesserae here. The mixed Sb-Mn glass with an intermediate composition was also used for

499

opaque glass however, most often for turquoise but also for pale grey-blue and yellow. Regional and

500

chronological variations in the availability of different glass types to use as a base may have played a

501

part, but it appears that glassworkers preferred certain base glass types for turquoise glass in particular

502

because similar trends have been identified amongst enamels and tesserae from a number of different

503

sites; these possibilities can be investigated further as more data becomes available.

M AN U

SC

RI PT

494

504

8.

Acknowledgments

506

We would like to thank Colchester Archaeological Trust, and also Dr Caroline Jackson and Professor

507

Jennifer Price for sharing their expertise on Roman opaque coloured glass. Thank you also to

508

anonymous referees for suggesting additional references to broaden the scope of the paper.

509

510

9.

511

Arletti, R., Quartieri, S., Vezzalini, G., 2006. Glass mosaic tesserae from Pompeii: an archaeometric

512

al investigation. Per Mineral 76, 25–38.

513

Barag, D., 1987. Recent Important Epigraphic Discoveries Related to the History of Glassmaking in

514

the Roman Period. In: Annales de l’Association Internationale pour l’Histoire du Verre v. 10, Madrid

515

and Segovia, 1985. AIHV, 109–116.

516

Bayley, J., 2001. Evidence for the production and use of opaque red glass in Roman Britain. In:

517

Annales du 15e Congrès de l’Association Internationale pour l’Histoire du Verre. AIHV, 45–8.

AC C

References

EP

TE D

505

ACCEPTED MANUSCRIPT Bayley, J., 2005. Roman enamel and enamelling: new finds from Castleford, Yorkshire. In: Annales

519

du 16e Congrès de l’Association Internationale pour l’Histoire du Verre. AIHV, 72–4.

520

Brill, R., 1999. Chemical analyses of early glasses. Volumes 1 and 2. New York.

521

Brooks, H., Holloway, B., 2007. An archaeological excavation on the site of the West Clacton

522

reservoir and pumping station, Dead Lane, Great Bentley, Essex April-May 2007. Colchester

523

Archaeological Trust Report No. 425, Colchester, doi: 10.5284/1022831,

524

http://archaeologydataservice.ac.uk/archives/view/greylit/details.cfm?id=28329

525

Brun, N., Pernot, M., Velde, B., 1989. Technique et science: les arts du verre Actes du colloque de

526

Namur, Facultés universitaires Notre-Dame de la Paix, Namur. Département d’histoire de l’art et

527

d’archéologie, 97.

528

Cagno, S., Cosyns, P., Izmer, A., Vanhaecke, F., Nys, K., Janssens, K., 2014. Deeply coloured and

529

black-appearing Roman glass: a continued research. Journal of Archaeological Science 42, 128–139.

530

Cool, H.E.M., 2007. The glass. In: Brooks, H. and Holloway, B. ibid.

531

Cool, H.E.M., Price, J., 1998. The vessels and objects of glass. In: Cool, H.E.M. and Philo, C. (Eds.),

532

Roman Castleford Excavations 1974-85. Volume I: the small finds. Yorkshire Archaeology 4, Leeds,

533

141–94.

534

Cool, H.E.M., Lloyd-Morgan, G., Hooley, A.D., 1995. Finds from the Fortress. Archaeology of York

535

17/10, CBA, York.

536

Di Bella, M., Quartieri, S., Sabatino, G., Santalucia, F., Triscari, M., 2014. The glass mosaics tesserae

537

of "Villa del Casale" (Piazza Armerina, Italy): a multi-technique archaeometric study, Archaeological

538

and Anthropological Sciences 6(4), 345–362.

539

Eichholz, D.E., 1962. Pliny, Natural History, vol. X, books XXXVI and XXXVII. Heinemann,

540

London.

AC C

EP

TE D

M AN U

SC

RI PT

518

ACCEPTED MANUSCRIPT Foster, H.E., Jackson, C.M., 2005. 'A whiter shade of pale'? Chemical and experimental investigation

542

of opaque white Roman glass gaming counters. Glass Technology 46 (5), 327–333.

543

Foy, D., Picon, M., Vichy, M., 2000a. Les matières premières du verre et la question des produits

544

semi-finis. Antiquité et Moyen Âge. In: Pétrequin, P., Fluzin, P., Thiriot, J., Benoit, P. (Eds.), Arts du

545

feu et productions artisanales. XX Recontres Internationales d’Archéologie et d’Histoire d’Antibes,

546

Antibes, 419–32.

547

Foy, D., Vichy, M., Picon, M., 2000b. Lingots de verre en Méditerrané occidentale. In: Annales du

548

14e Congrès de l’Association Internationale pour l’Histoire du Verre. Amsterdam, AIHV, 51–57.

549

Fredrickx, P., De Ryck, I., Janssens, K., Schryvers, D., Petit J. –P., Döcking, H., 2004. EPMA and µ-

550

SRXRF analysis and TEM-based microstructure characterization of a set of Roman glass fragments.

551

X-ray Spectrometry 33, 326–333.

552

Freestone, I.C., Gorin-Rosen, Y., Hughes, M.J., 2000. Primary glass from Israel and the production of

553

glass in Late Antiquity and the Early Islamic Period. In: Nenna, M-Do. (Ed.), La route du verre:

554

ateliers primaires et secondaires de verriers du second millienium av. J.-C au Moyen-Age. Travaux et

555

la Maison de l’Orient Mediterranean No. 33, Lyon, 65–83.

556

Freestone, I. C., Stapleton, C. P., Rigby, V., 2003. The production of red glass and enamel in the Late

557

Iron Age, Roman and Byzantine periods. In: Entwistle C. (Ed.), Through a glass brightly – studies in

558

Byzantine and medieval art and archaeology presented to David Buckton. Oxbow, 142–154.

559

Galli, S., Mastelloni, M., Ponterio, R., Sabatino, G., Triscari, M., 2004. Raman and scanning electron

560

microscopy and energy-dispersive X-ray techniques for the characterization of coloring and

561

opaquening agents in Roman mosaic glass tesserae, Journal of Raman Spectroscopy 35, 622–627.

562

Gedzevičiūtė, V., Welter, N., Schüssler, U., Weiss, C., 2009. Chemical composition and colouring

563

agents of Roman mosaic and millefiori glass, studied by electron microprobe analysis and Raman

564

microspectroscopy. Archaeological and Anthropological Sciences 1(1), 15–29.

AC C

EP

TE D

M AN U

SC

RI PT

541

ACCEPTED MANUSCRIPT Gliozzo, E., Santagostino Barbone, A., Turchiano, M., Memmi, I., Volpe, G., 2012. The coloured

566

tesserae decorating the vaults of the Faragola Balneum (Ascoli Satriano, Foggia, southern Italy).

567

Archaeometry 54, 311–331.

568

Heck, M., Rehren, Th., Hoffmann, P., 2003. The Production of Lead–Tin Yellow at Merovingian

569

Schleitheim (Switzerland). Archaeometry, 45, 33–44.

570

Henderson, J., 1991. The technological characteristics of Roman enamels. Jewellery Studies 5, 65–76.

571

Henderson, J., 1996. Scientific analysis of selected Fishbourne vessel glass and its archaeological

572

interpretation. In: Cunliffe, B., Down, A. and Rudkin, D. (Eds.), Excavations at Fishbourne 1969-

573

1988. Chichester Excavations 9, Chichester, 189–192.

574

Jackson, C.M., Paynter, S., 2015. A great big melting pot: exploring patterns of glass supply,

575

consumption and recycling in Roman Coppergate, York. Archaeometry. doi: 10.1111/arcm.12158.

576

Jackson, C.M., Price, J. and Lemke, C., 2009. Glass production in the 1st century A.D. Insights into

577

glass technology. Annales du 17e Congrès de l’Association Internationale pour l’Histoire du Verre,

578

Antwerp 2006, 150–156.

579

Jackson, C.M., Cottam, S., 2015. ‘A green thought in a green shade’; compositional and typological

580

observations concerning the production of emerald green glass vessels in the 1st century A.D. Journal

581

of Archaeological Science 61, 139–148.

582

Jackson, C.M., 1994. Tables A1 and A2. In: Baxter, M.J., Exploratory multivariate analysis in

583

archaeology. Edinburgh University Press, Edinburgh, 228–231.

584

Jackson, C.M., 2005. ‘Making colourless glass in the Roman period’. Archaeometry 47, 763–780.

585

Janssens, K.H.A., 2013. Modern methods for analysing archaeological and historical glass. Wiley.

586

Kunicki-Goldfinger, J.J., Freestone, I.C., McDonald, I., Hobot J.A., Gilderdale-Scott, H., Ayers, T.,

587

2014. Technology, production and chronology of red window glass in the medieval period –

588

rediscovery of a lost technology. Journal of Archaeological Science 41, 89–105.

AC C

EP

TE D

M AN U

SC

RI PT

565

ACCEPTED MANUSCRIPT Lahlil, S., Biron, I., Galoisy, L., Morin, G., 2008. Rediscovering ancient glass technologies through

590

the examination of opacifier crystals. Journal of Applied Physics A 92, 109–116.

591

Lahlil, S., Biron, I., Cotte, M., Susini, J., 2010a. New insight on the in situ crystallization of calcium

592

antimonate opacified glass during the Roman period. Applied Physics A 100, 683-692.

593

Lahlil, S., Biron, I., Cotte, M., Susini, J., Menguy, N., 2010b. Synthesis of calcium antimonate nano-

594

crystals by the 18th dynasty Egyptian glassmakers. Applied Physics 98, 1–8.

595

Lemke, C., 1998. Reflections of the Roman Empire: the first century glass industry seen through

596

traditions of manufacture. In: McCray, P., McCray, P. (Eds.), The prehistory and history of

597

glassmaking technology. American Ceramics Society, Ohio, 269–291.

598

Mass, J.L., Stone, R.E., Wypyski, M.T., 1998. The mineralogical and metallurgical origins of Roman

599

opaque coloured glasses. In: Kingery, W.D., McCray, P. (Eds.), The prehistory and history of

600

glassmaking technology. American Ceramics Society, Ohio, 121–144.

601

Mass, J.L., Wypiski, M.T., Stone, R.E., 2002. Malkata and Lisht glassmaking technologies: towards a

602

specific link between second millennium BC metallurgists and glassmakers. Archaeometry 44, 67–82.

603

Mirti, P., Pace, M., Negro Ponzi M.M., Aceto, M., 2008. ICP–MS analysis of glass fragments of

604

Parthian and Sasnian epoch from Seleucia and Veh Ardašar (central Iraq). Archaeometry 50 (3), 429–

605

450.

606

Nenna, M-Do., Gratuze, B., 2009. Étude diachronique des compositions de verres employés dans les

607

vases mosaïques antiques: résultats préliminaires. In: Janssens, K. (Ed.), Annales du 17e congrès

608

d'Association Internationale pour l'Histoire du Verre, 2006. Aspeditions, Antwerp, 199–205.

609

Nenna, M.D., Vichy, M. and Picon, M., 1997. L’atelier de verrier de Lyon, du siècle après J.-C., et

610

l’origine des verres Romains. Revue d’Archèomètrie 21, 81–7.

611

Paynter, S., 2006. Analyses of colourless Roman glass from Binchester, County Durham. Journal of

612

Archaeological Science 33, 1037–1057.

AC C

EP

TE D

M AN U

SC

RI PT

589

ACCEPTED MANUSCRIPT Paynter, S., Kearns, T., 2011. West Clacton Reservoir, Great Bentley, Essex. Analysis of Glass

614

Tesserae. Unpublished English Heritage Research Department Report No. 44–2011.

615

Paynter, S., Schibille, N., forthcoming. The polychrome glass from Roman Chester. In: Edwards, J.,

616

Paynter, S. (Eds.), Recent research and new discoveries in glass and ceramics: proceedings of the

617

conference in memory of Sarah Jennings. MPRG Occasional Paper, MPRG, London.

618

Picon, M., Thirion-Merle, V., Vichy, M., 2008. Les verres au natron et les verres aux cendres du Wadi

619

Natrun (Egypte). Bulletin de l’Association Française pour l’Archéologie du Verre, 36–41.

620

Price, J., Cottam, S., 1998. Romano-British glass vessels: a handbook. Practical Handbooks in

621

Archaeology No. 14, CBA, York.

622

Rehren, Th., Kraus, K., 1999. Cupel and crucible: the refining of debased silver in the Colonia Ulpia

623

Traiana, Xanten. Journal of Roman Archaeology 12, 263–272.

624

Rehren, Th., 2003. Comments on J. L. Mass, M. T. Wypiski and R. E. Stone, ‘Malkata and Lisht

625

glassmaking technologies: towards a specific link between second millennium BC metallurgists and

626

glassmakers’. Archaeometry 45, 185–198.

627

Ricciardia, P., Colombana, P., Tourniéa, A., Macchiarolab, M., Ayedc, N., 2009. A non-invasive

628

study of Roman Age mosaic glass tesserae by means of Raman spectroscopy. Journal of

629

Archaeological Science 36(11), 2551–2559.

630

Roman Glassmakers, 2002. Sealing wax red. Unpublished Newsletter 3,

631

http://www.romanglassmakers.co.uk/

632

Sayre, E.V., Smith, R.W., 1967. Some materials of glass manufacturing in Antiquity. In: Levey, M.,

633

(Ed.), Archaeological chemistry. University of Pennsylvania Press, Pennsylvania, pp. 279–311.

634

Shortland, A., J., 2002. The use and origin of antimonate colorants in early Egyptian glass.

635

Archaeometry 44(4), 517–530.

AC C

EP

TE D

M AN U

SC

RI PT

613

ACCEPTED MANUSCRIPT Silvestri, A., Molin, G. and Salviulo, G., 2008, The colourless glass of Iulia Felix, Journal of

637

Archaeological Science, 35, 331-341.

638

Silvestri, A., Tonietto, S., Molin, G., Guerriero, P., 2012. The palaeo-Christian glass mosaic of St.

639

Prosdocimus (Padova, Italy): archaeometric characterisation of tesserae with antimony- or

640

phosphorus-based opacifiers. Journal of Archaeological Science 39(7), 2177–2190.

641

Stapleton, C.P., Freestone, I.C., Bowman, S.G.E., 1999. Composition and origin of early mediaeval

642

opaque red enamel from Britain and Ireland. Journal of Archaeological Science 26, 913–921.

643

Turner, W.E.S., 1956. Studies in ancient glasses and glassmaking processes, part V: raw materials and

644

melting processes. Glass Technology 40, 277–300.

645

van der Werf, I., Mangone, A., Giannossa, L.C., Traini, A., Laviano, R., Coralini, A., Sabbatini, L.,

646

2009. Archaeometric investigation of Roman tesserae from Herculaneum (Italy) by the combined use

647

of complementary micro-destructive analytical techniques. Journal of Archaeological Science 36,

648

2625–2634.

649

Vicenzi, E. P., Eggins, S., Logan, A., Wysoczanski, R., 2002. Microbeam characterization of Corning

650

archaeological reference glasses: new additions to the Smithsonian microbeam standard collection.

651

Journal of Research of the National Institute of Standards and Technology 107, 719–727.

652

Wedepohl, K.H., Baumann, A., 2000. The use of marine molluskan shells for Roman glass and local

653

raw glass production in the Eifel area (Western Germany). Naturwissen 87(3), 129–132.

654

Weyl, W., 1953. Coloured glasses. Society of Glass Technology, Sheffield.

655

Zienkiewicz, J.D., 1993. Excavations at the Scamnum Tribunorum at Caerleon: the Legionary

656

Museum Site, 1983–5. Britannia 24, 27–140.

M AN U

TE D

EP

AC C

657 658

SC

RI PT

636

Captions

ACCEPTED MANUSCRIPT 659

Tables

661

Table 1: SEM-EDS analyses of glass standards (wt%), average of 5 analyses, and ICP-MS analyses of

662

standards (wt% and ppm), bd = below detection limit, compared with reported values (Vicenzi et al.

663

2002).

RI PT

660

664

Table 2: Composition of tesserae and cakes (wt%), average of at least 3 SEM-EDS, analyses of bulk

666

areas, bd = below detection

SC

665

667

Appendix A: SEM-EDS data for the tesserae in wt%, normalised, with probable base glass: Mn, Sb,

669

Sb-Mn or PA (plant ash component).

670 671

Appendix B: ICP-MS data for selected tesserae, ppm

Figures

674

TE D

672 673

M AN U

668

Figure 1: Some of the analysed tesserae, clockwise from top left: samples 24 and 20 (opaque red), 18

676

(translucent emerald green), 17 (opaque emerald green), 6 (mid-green), 51 (opaque yellow), 12 and 14

677

(opaque turquoise), 67 (opaque pale grey-blue), 19 (transparent dark blue) and 176 (opaque dark to

678

mid-blue).

679

Figure 2: The fragments of the opaque dark to mid-blue and turquoise cakes of glass (left and right

680

respectively) and one each of the tesserae cut from the cakes (bottom centre).

681

Figures 3a, b and c: Plots of the ICP-MS results (ppm) and average SEM-EDS results (wt% oxides)

682

for lead, copper and antimony respectively for the West Clacton samples analysed by both techniques.

AC C

EP

675

ACCEPTED MANUSCRIPT Figure 4: Plot comparing the average bulk compositions of the West Clacton cakes and tesserae to the

684

three main types of raw Roman natron glass, and the mixed Sb-Mn glass resulting from recycling

685

(data from Jackson and Paynter 2015). The hollow circle is the translucent dark blue tesserae 19, with

686

<0.05wt% MnO (made with Sb base glass), the grey-filled circles are tesserae and cakes containing

687

0.05-0.3wt% MnO (turquoise cake and tesserae 15 and 12, and yellow tessera 64, all made with Sb-

688

Mn base glass) and the solid circles contain the most MnO, >0.3wt% (cobalt blue tesserae and cake,

689

yellow and green tesserae, made with Mn base glass).

690

Figure 5: A plot showing the potassium and magnesium oxide concentrations in the West Clacton

691

tesserae (reduced compositions) compared to emerald green vessel glass (from Henderson 1996 and

692

Lemke 1998).

693

Figure 6a: A plot showing the correlation between the concentrations of antimony, arsenic and lead in

694

the cobalt coloured glass (ppm by ICP-MS, wt% oxides based on average composition by SEM-EDS).

695

Solid symbols are for opaque blue glass, grey-filled symbol is pale grey-blue glass, and hollow

696

symbol is transparent blue glass.

697

Figure 6b: A plot showing the correlation between the concentrations of cobalt, copper and nickel in

698

the cobalt coloured glass (ppm by ICP-MS). Solid symbols are for opaque blue glass, grey-filled

699

symbol is pale grey-blue glass, and hollow symbol is transparent blue glass.

700

Figure 7: SEM image of an opaque turquoise tessera showing large potassium antimonate crystals

701

(white), voids (black) and scattered small calcium antimonate CaSb2O6 crystals (white flecks).

702

Figure 8: An SEM image of a dissolving mixed mineral inclusion in a yellow tessera, including many

703

feldspar grains (dark grey), with increased concentrations of lead in the vicinity of the inclusion (light

704

grey areas) and small lead antimonate crystals (white flecks) surrounding it.

705

AC C

EP

TE D

M AN U

SC

RI PT

683

ACCEPTED MANUSCRIPT

1.20 Na2O 14.12 14.30 16.20 17.00 14.80 14.39

K2 O 2.56 2.84 1.18 1.00 13.92 11.30 K2O 3.05 2.87 1.17 1.00 0.43 0.41

CaO 4.64 5.07 10.02 8.56 18.30 14.80 CaO 5.30 5.03 8.96 8.56 7.29 7.11

TiO2 0.81 0.79 0.09 0.09 0.31 0.38 TiO2 0.88 0.79 0.13 0.09 0.02 0.02

MnO bd 0.82 0.26 0.25 0.56 0.55 MnO 1.06 1.00 0.25 0.25 <0.1 -

Fe2O3 0.27 0.34 0.33 0.34 0.40 0.52 Fe2O3 1.02 1.09 0.31 0.34 <0.1 0.04

CoO 0.19 0.18 0.05 0.05 0.02 0.02 CoO 0.17 0.17 <0.1 0.05 <0.1 -

RI PT

Known SEM-EDS Corning A Measured Known Corning B Measured Known NIST 620 Measured Known

SO3 <1.2 0.10 1.43 0.50 <1.2 0.30 SO3 0.20 0.10 0.65 0.50 0.27 0.28

SC

17.00

P2O5 0.06 0.14 0.68 0.82 4.15 3.93 P2O5 0.15 0.13 0.85 0.82 <0.1 bd

M AN U

Known

Corning D Measured 1.74

SiO2 nm 34.87 nm 61.55 nm 55.24 SiO2 66.84 66.56 60.38 61.55 72.43 72.08

TE D

1.07

Al2O3 0.74 0.87 5.02 4.36 6.49 5.30 Al2O3 0.96 1.00 4.14 4.36 1.90 1.80

EP

Known

Corning B Measured 20.63

MgO 2.42 2.76 1.24 1.03 5.06 3.94 MgO 2.71 2.66 1.01 1.03 3.84 3.69

AC C

Na2O

ICP-MS

Corning C Measured 1.02

CuO 1.17 1.13 2.83 2.66 0.37 0.38 CuO 1.25 1.17 2.79 2.66 <0.1 -

SnO2 0.17 0.19 0.01 0.04 0.02 0.10 SnO2 0.29 0.19 <0.2 0.04 <0.2 -

Sb2O5 0.00 0.03 0.24 0.46 0.20 0.97 Sb2O5 1.92 1.75 0.62 0.46 <0.2 -

BaO 11.77 11.40 0.09 0.12 0.34 0.51 BaO 0.46 0.56 <0.2 0.12 <0.2 -

PbO 39.45 36.70 0.53 0.61 0.25 0.48 PbO <0.2 0.12 0.51 0.61 <0.2 -

ACCEPTED MANUSCRIPT

0.14 0.05 0.14 0.04 <0.1 0.17 0.03 0.17 0.04 0.24 0.05 0.14 0.02 0.13 0.03 0.14 0.03 0.21 0.06 0.15 0.01 0.15 0.05 0.10 0.05 0.15 0.02 0.17 0.06

0.27 0.07 0.33 0.03 0.34 0.06 0.32 0.09 0.29 0.06 0.34 0.02 0.45 0.07 0.34 0.10 0.31 0.13

1.23 0.02 1.05 0.03 1.07 0.02 1.10 0.04 1.34 0.03 1.18 0.04 1.12 0.03 0.90 0.03 1.16 0.03 1.14 0.02 1.23 0.05 1.20 0.03 1.23 0.05 1.09 0.02 1.15 0.06 1.17 0.05 1.15 0.07 1.08 0.03 0.75 0.02 1.03 0.01 1.04 0.15

<0.1 -

TiO2

CaO 2.11 0.02 2.00 0.06 2.07 0.06 0.63 0.02 0.71 0.04 0.62 0.02 0.73 0.03 0.59 0.03 0.64 0.03 0.69 0.03 0.72 0.04 0.64 0.04 0.59 0.03 0.67 0.01 0.71 0.05 0.65 0.03 0.62 0.03 0.65 0.03 0.63 0.03 0.67 0.03 0.65 0.05

7.17 0.02 6.95 0.13 7.05 0.10 4.80 0.04 5.50 0.13 5.65 0.28 6.71 0.05 6.35 0.08 6.87 0.09 6.59 0.08 6.52 0.07 6.82 0.04 6.71 0.06 7.27 0.04 7.05 0.22 7.21 0.08 7.04 0.12 7.18 0.16 6.37 0.07 7.08 0.05 7.27 0.31

MnO 0.21 0.04 0.17 0.05 0.19 0.02 0.13 0.01

<0.1 0.13 0.02 <0.1 -

FeO

0.13 0.02

<0.1 -

0.13 0.02

<0.1 <0.1 <0.1 <0.1 <0.1 -

0.11 0.00 0.13 0.01 <0.1 <0.1 <0.1 <0.1 -

0.93 0.03 0.90 0.06 0.90 0.03 0.47 0.06 0.24 0.01 0.44 0.06 0.58 0.02 0.83 0.02 0.31 0.03 0.45 0.04 0.60 0.02 0.44 0.06 0.44 0.04 0.65 0.03 0.53 0.05 0.69 0.04 0.47 0.08 0.58 0.04 0.72 0.04 0.69 0.04 0.57 0.13

1.69 0.05 1.55 0.07 1.61 0.03 0.94 0.07 0.61 0.05 0.67 0.09 0.66 0.03 0.57 0.03 0.53 0.03 0.64 0.04 0.52 0.06 0.59 0.03 0.61 0.05 0.70 0.03 0.55 0.04 0.64 0.06 0.56 0.09 0.69 0.06 0.87 0.01 0.67 0.06 0.68 0.13

CoO <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 -

CuO

RI PT

<0.1 <0.1 -

K2 O

Cl 0.28 0.04 0.28 0.07 0.27 0.04 0.30 0.06 0.47 0.11 0.30 0.04 0.27 0.08 0.30 0.05 0.22 0.03 0.31 0.01 0.27 0.04 0.21

SC

SO3 1.18 0.02 1.10 0.09 1.08 0.01

M AN U

P2O5 53.69 0.28 61.19 0.45 61.48 0.13 60.63 0.48 61.95 0.24 64.18 1.45 63.89 0.36 58.04 0.21 66.95 0.24 64.06 0.28 68.77 0.12 66.58 0.57 66.96 0.43 67.07 0.13 68.35 0.45 67.61 0.27 67.85 0.60 66.80 0.32 63.30 0.38 67.01 0.25 66.85 1.56

TE D

SiO2 2.14 0.03 2.21 0.04 2.18 0.01 1.96 0.08 2.58 0.19 2.07 0.06 2.27 0.08 2.52 0.07 2.42 0.01 2.25 0.06 2.21 0.16 2.20 0.11 2.14 0.07 2.25 0.03 2.38 0.06 2.29 0.05 2.32 0.08 2.29 0.06 2.16 0.04 2.30 0.07 2.26 0.07

EP

Na2O Al2O3 MgO 13.30 2.79 0.19 0.07 15.60 2.71 0.37 0.00 15.34 2.61 0.16 0.11 15.97 0.49 0.09 0.06 16.85 0.46 0.39 0.04 15.99 0.48 0.42 0.06 15.48 0.57 0.11 0.04 13.47 0.51 0.05 0.03 15.74 0.45 0.14 0.03 15.21 0.45 0.17 0.09 15.99 0.61 0.12 0.04 15.18 0.41 0.10 0.06 14.78 0.41 0.07 0.04 15.85 0.45 0.07 0.06 16.11 0.49 0.32 0.02 16.20 0.47 0.13 0.05 17.20 0.51 0.29 0.04 16.58 0.51 0.18 0.04 15.48 0.42 0.08 0.02 16.42 0.52 0.08 0.03 16.31 0.51 0.49 0.03

AC C

Avg StDev Avg StDev Avg StDev Avg StDev Avg StDev Avg StDev Avg StDev Avg StDev Avg StDev Avg StDev Avg StDev Avg StDev Avg StDev Avg StDev Avg StDev Avg StDev Avg StDev Avg StDev Avg StDev Avg StDev Avg StDev

<0.1 <0.1 <0.1 0.34 0.03

<0.1 <0.1 -

<0.1 <0.1 <0.1 -

ZnO 2.11 0.04 1.80 0.03 1.79 <0.1 0.02 <0.1 <0.1 <0.1 2.61 <0.1 0.05 1.65 <0.1 0.04 1.12 <0.1 0.15 0.97 <0.1 0.01 0.15 <0.1 0.05 0.74 <0.1 0.05 0.35 <0.1 0.04 0.13 <0.1 0.04 0.12 <0.1 0.01 <0.1 <0.1 <0.1 0.46 <0.1 0.02 0.13 <0.1 0.02 0.11 <0.1 0.00 -

SnO2 0.14 0.05 0.11 0.02

Sb2O5 0.84 0.15 0.42 0.15 0.46 0.05

<0.2 0.23 0.04 <0.2 0.41 0.08 <0.2 <0.2 0.24 0.03 <0.2 0.28 0.01 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 -

PbO 0.39 0.06 0.39 0.04 0.21 0.00 1.48 0.06 1.12 0.20 0.83 0.20 0.49 0.09 1.16 0.09 0.25 0.03 0.52 0.14 0.30 0.09 0.36 0.06 0.29 0.06 1.81 0.22 1.24 0.34 1.44 0.13 0.96 0.44 1.63 0.27 5.70 0.27 1.67 0.16 1.76 0.99

9.96 0.13 1.63 0.11 1.62 0.12 10.93 0.46 7.87 0.43 7.23 1.90 4.16 0.32 12.80 0.09 2.90 0.31 6.27 0.22 1.64 0.10 4.22 0.62 5.10 0.61 1.45 0.10 0.69 0.17 0.95 0.14 0.67 0.36 1.36 0.11 2.05 0.09 1.18 0.06 1.34 0.82

ACCEPTED MANUSCRIPT

0.13 0.04 0.19 0.04 0.15 0.02 0.15 0.02 0.17 0.04 0.17 0.07 0.46 0.01 0.15 0.01 <0.1 <0.1 <0.1 <0.1 -

0.32 0.07 0.33 0.06 0.28 0.00 0.33 0.03 0.54 0.06 0.53 0.06 0.47 0.07 0.24 0.03 0.24 0.03 0.40 0.09 0.59 0.06 0.36 0.05 0.42 0.04

1.19 0.04 1.18 0.09 1.20 0.02 1.13 0.02 1.02 0.06 0.97 0.02 0.91 0.02 1.22 0.03 1.23 0.02 1.56 0.02 1.05 0.03 1.54 0.03 1.40 0.04

0.61 0.01 0.63 0.03 0.57 0.04 0.66 0.03 0.67 0.04 0.62 0.03 0.65 0.01 1.11 0.02 0.68 0.04 0.57 0.02 0.61 0.02 0.62 0.03 0.54 0.06

7.00 0.05 7.63 0.20 7.68 0.04 7.02 0.05 6.16 0.16 5.94 0.04 6.50 0.08 6.86 0.04 7.16 0.08 5.68 0.04 5.15 0.04 5.73 0.06 5.59 0.07

<0.1 <0.1 <0.1 <0.1 <0.1 0.12 0.03 0.09 0.04 0.12 0.01 0.14 0.03 0.15 0.01 0.11 0.01 0.15 0.02 0.12 <0.1 0.03 -

0.42 0.02 0.51 0.13 0.48 0.02 0.68 0.04 0.29 0.02 0.24 0.02 0.46 0.04 0.93 0.02 0.38 0.02 0.22 0.02 0.09 0.04 0.20 0.03

0.56 0.03 0.49 0.11 0.46 0.04 0.63 0.07 0.69 0.03 0.67 0.03 0.62 0.02 0.67 0.05 2.56 0.07 0.56 0.02 0.53 0.01 0.54 0.08 0.63 0.04

<0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 -

RI PT

<0.1 -

SC

67.64 0.32 68.83 0.99 69.30 0.16 66.96 0.17 65.94 0.25 65.62 0.19 66.04 0.19 65.66 0.24 67.63 0.21 65.66 0.15 64.20 0.22 65.62 0.09 68.89 0.35

M AN U

2.29 0.04 2.37 0.07 2.42 0.05 2.25 0.09 2.28 0.03 2.24 0.04 2.34 0.09 2.17 0.05 2.36 0.07 2.10 0.03 2.10 0.08 2.13 0.07 1.82 0.04

TE D

0.51 0.03 0.47 0.05 0.48 0.02 0.50 0.04 0.52 0.05 0.58 0.06 0.47 0.05 1.25 0.04 0.52 0.06 0.53 0.04 0.42 0.04 0.54 0.03 0.34 0.03

EP

17.30 0.15 15.43 0.32 16.00 0.07 16.39 0.10 17.80 0.11 18.46 0.10 17.05 0.05 16.47 0.08 16.61 0.15 19.05 0.26 18.37 0.20 19.13 0.11 18.50 0.17

AC C

Avg StDev Avg StDev Avg StDev Avg StDev Avg StDev Avg StDev Avg StDev Avg StDev Avg StDev Avg StDev Avg StDev Avg StDev Avg StDev

<0.1 0.11 0.01 0.17 <0.1 0.13 0.03 <0.1 <0.1 <0.1 1.96 0.04 <0.1 0.97 0.05 2.79 0.04 0.98 0.05 0.14 0.03

<0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 -

<0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 -

1.08 0.21 1.00 0.64 0.42 0.03 1.71 0.14 3.43 0.19 3.44 0.16 3.98 0.14 0.21 0.22 0.34 0.20 2.28 0.03 3.57 0.26 2.05 0.03 1.09 0.09

0.70 0.07 0.77 0.59 0.37 0.04 1.24 0.09 0.32 0.11 0.28 0.07 0.18 0.08 0.41 0.11 0.09 0.08 0.20 0.08 0.23 0.09 0.29 0.05 0.25 0.11

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

SC

RI PT

ACCEPTED MANUSCRIPT

M AN U

140000

100000 80000

TE D

60000 40000 20000

0

EP

0 2

AC C

Pb (ICP-MS ppm)

120000

4

6

8

PbO (wt% SEM-EDS)

10

12

14

SC

RI PT

ACCEPTED MANUSCRIPT

M AN U

25000

15000

5000 0 0.0

EP

TE D

10000

0.5

AC C

Cu (ICP-MS ppm)

20000

1.0

1.5 CuO (wt% SEM-EDS)

2.0

2.5

3.0

ACCEPTED MANUSCRIPT

RI PT

25000

SC M AN U

15000

TE D

10000

EP

5000

0 0

AC C

Sb (ICP-MS ppm)

20000

1

2

3 Sb2O5 (wt% SEM-EDS)

4

5

6

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT Highlights Transparent blue-green (aqua) glass was used as the base for most opaque colours.

•

Changes in base glass composition affect the formation of opacifying crystals.

•

Mixed Sb-Mn (and possibly colourless antimony) glass was used for opaque turquoise.

•

Colourless antimony glass was used to make transparent deep blue glass.

AC C

EP

TE D

M AN U

SC

RI PT

•

ACCEPTED MANUSCRIPT

WC23

Red

PA

WC62

Yellow

Sb-Mn

WC64

Yellow

Sb-Mn

WC30

Yellow/ Green

Mn

WC3

Green

Mn

WC6

Green

Mn

WC9

Green/ Yellow

Mn

WC11

Green/ Yellow

Mn

WC35

Yellow/ Green

Mn

WC51

Yellow/ Green

Mn

SiO2 53.34 53.61 53.81 54.00 61.05 60.83 61.69 61.43 61.33 61.51 61.63 60.85 60.88 59.91 60.87 61.84 61.74 61.92 62.28 64.11 63.92 64.52 65.07 65.86 61.6 64.19 64.18 63.45 63.73 57.9 58.39 58.09 57.94 57.9 66.67 67.24 66.9 66.98 63.85 64.47 64.03 63.9 68.71 68.65 68.93 68.79 66.02 66.39

P2O5 1.18 1.18 1.16 1.21 1.17 1.00 1.12 1.08 1.09 1.08 1.08 <0.1 <0.1 <0.1 <0.1 0.08 0.12 <0.1 <0.1 <0.1 0.1 <0.1 <0.1 0.17 <0.1 <0.1 0.16 0.11 <0.1 <0.1 <0.1 <0.1 0.13 <0.1 0.15 0.16 0.16 0.22 0.22 0.14 0.13 0.18 0.28 0.19 <0.1 0.26 0.13 0.14

SO3 <0.2 0.25 0.31 <0.2 0.21 0.35 0.29 0.3 0.28 0.2 0.28 0.29 0.22 0.32 0.36 0.57 0.55 0.33 0.42 0.26 0.32 0.29 0.34 0.25 0.34 <0.2 <0.2 0.21 0.32 0.34 0.33 0.25 0.24 0.34 0.21 0.25 0.2 <0.2 <0.2 <0.2 0.3 0.31 0.23 0.27 0.3 <0.2 0.21 <0.2

Cl 1.21 1.22 1.23 1.25 1.06 1.07 1.01 1.07 1.09 1.05 1.06 1.14 1.06 1.09 1.12 1.38 1.32 1.30 1.35 1.15 1.22 1.20 1.17 1.23 1.13 1.15 1.12 1.09 1.10 0.93 0.86 0.88 0.91 0.93 1.12 1.17 1.16 1.20 1.14 1.17 1.14 1.12 1.17 1.25 1.29 1.2 1.17 1.24

K2O 2.13 2.13 2.09 2.09 2.00 1.95 2.06 2.05 2.04 2.16 2.02 0.61 0.65 0.64 0.61 0.75 0.69 0.73 0.66 0.62 0.63 0.61 0.60 0.65 0.60 0.74 0.69 0.73 0.75 0.60 0.54 0.59 0.61 0.60 0.67 0.60 0.63 0.65 0.68 0.68 0.66 0.72 0.69 0.69 0.75 0.76 0.59 0.66

CaO 7.18 7.14 7.17 7.19 6.99 6.81 7.06 7.12 7.13 7.04 6.92 4.76 4.84 4.76 4.82 5.64 5.37 5.41 5.57 5.44 5.63 5.83 5.75 6.01 5.23 6.68 6.78 6.66 6.72 6.29 6.48 6.38 6.3 6.29 6.94 6.95 6.81 6.77 6.55 6.52 6.69 6.61 6.45 6.48 6.54 6.61 6.76 6.82

TiO2 0.25 0.23 0.18 0.18 0.19 0.12 0.21 0.17 0.19 0.21 0.19 0.12 0.11 0.14 0.13 0.14 <0.1 <0.1 <0.1 0.15 0.14 0.12 0.14 0.12 0.10 <0.1 0.10 <0.1 <0.1 0.12 <0.1 0.11 0.15 0.12 0.1 <0.1 <0.1 <0.1 <0.1 0.14 0.1 0.14 0.1 0.1 <0.1 <0.1 <0.1 <0.1

MnO 0.98 0.93 0.92 0.9 0.97 0.87 0.86 0.92 0.89 0.92 0.86 0.42 0.45 0.44 0.55 0.23 0.23 0.24 0.25 0.55 0.43 0.42 0.4 0.45 0.41 0.57 0.60 0.59 0.55 0.84 0.85 0.83 0.81 0.84 0.3 0.32 0.33 0.27 0.48 0.48 0.41 0.42 0.63 0.58 0.58 0.59 0.46 0.41

FeO 1.61 1.71 1.71 1.71 1.62 1.49 1.54 1.6 1.57 1.6 1.65 0.95 0.96 1.01 0.84 0.55 0.64 0.66 0.6 0.55 0.77 0.67 0.64 0.59 0.78 0.62 0.67 0.7 0.66 0.57 0.53 0.55 0.62 0.57 0.56 0.48 0.53 0.53 0.60 0.62 0.66 0.69 0.48 0.6 0.51 0.47 0.62 0.57

RI PT

PA

Al2O3 2.16 2.13 2.17 2.11 2.2 2.25 2.18 2.17 2.20 2.18 2.17 2.00 2.05 1.88 1.92 2.45 2.84 2.61 2.42 1.99 2.13 2.05 2.11 2.12 2.02 2.21 2.21 2.37 2.3 2.54 2.41 2.59 2.51 2.54 2.41 2.44 2.43 2.41 2.22 2.17 2.30 2.30 2.14 2.45 2.13 2.11 2.21 2.18

SC

Red

MgO 2.85 2.84 2.77 2.69 2.71 2.71 2.71 2.62 2.70 2.66 2.46 0.47 0.42 0.51 0.55 0.48 0.46 0.48 0.40 0.61 0.43 0.47 0.47 0.47 0.45 0.62 0.56 0.54 0.55 0.48 0.51 0.55 0.52 0.48 0.42 0.45 0.48 0.44 0.45 0.57 0.39 0.38 0.65 0.58 0.57 0.63 0.44 0.36

M AN U

WC25

Na2O 13.41 13.51 13.12 13.15 15.62 15.96 15.23 15.43 15.22 15.18 15.51 15.95 16.07 15.99 15.85 17.21 16.33 16.77 17.07 15.93 16.18 15.88 16.07 16.57 15.30 15.57 15.4 15.38 15.58 13.51 13.39 13.45 13.51 13.51 15.71 15.88 15.82 15.55 15.15 15.03 15.21 15.44 15.95 16.17 15.9 15.94 15.11 15.08

TE D

Base PA

EP

Colour Red

AC C

Sample WC20

CoO <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 0.1 <0.1 <0.1 <0.1 <0.1

CuO 2.07 2.10 2.11 2.16 1.77 1.80 1.82 1.77 1.76 1.80 1.81 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 2.59 2.67 2.64 2.55 1.63 1.64 1.71 1.62 1.63 1.13 0.93 1.30 1.10 0.96 0.96 0.97 0.98 0.18 0.1 0.12 0.2 0.77 0.78

ZnO <0.1 <0.1 0.18 0.19 <0.1 0.11 0.13 <0.1 <0.1 <0.1 0.1 <0.1 0.15 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 0.13 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 0.11 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1

SnO2 1.06 0.74 0.81 0.74 0.45 0.55 0.25 0.41 0.50 0.51 0.41 <0.2 <0.2 <0.2 <0.2 0.2 <0.2 0.25 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 0.4 0.32 0.4 0.51 <0.2 <0.2 <0.2 0.21 <0.2 <0.2 0.22 <0.2 <0.2 0.26 <0.2 0.21 0.24 0.24 <0.2 <0.2 0.2 <0.2 0.28

Sb2O5 0.43 0.35 <0.2 <0.2 0.41 0.36 <0.2 0.21 <0.2 <0.2 0.21 1.41 1.45 1.55 1.5 1.12 1.26 1.26 0.84 0.91 0.89 0.72 0.75 0.56 1.15 0.46 <0.2 0.41 0.59 1.23 1.07 1.06 1.22 1.23 0.25 0.21 0.26 0.29 0.69 0.35 0.47 0.56 0.4 0.22 0.34 0.23 0.36 0.42

PbO 9.87 9.84 10.1 10.04 1.53 1.75 1.61 1.45 1.71 1.71 1.6 10.89 10.52 11.58 10.73 7.24 8.23 7.94 8.05 7.35 7.12 6.96 6.3 4.97 10.69 3.91 4.15 4.61 3.95 12.83 12.82 12.89 12.65 12.83 3.18 2.59 2.66 3.15 6.41 6.39 6.32 5.95 1.67 1.48 1.7 1.69 4.9 4.31

ACCEPTED MANUSCRIPT

WC108

MidMn translucent blue

WC102

Mid(trans) blue

Mn

WC166

Midblue

Mn

WC147

Midblue

Mn

WC179

Midblue

Mn

WC88

Mid(trans) blue

Mn

WC176

Midblue

Mn

WC82

Pale blue Mn cloudy

1.2 1.19 1.15 1.26 1.26 1.24 1.06 1.11 1.09 1.10 1.14 1.13 1.23 1.10 1.11 1.23 1.19 1.15 1.15 1.15 1.27 1.23 1.11 1.18 1.2 1.06 1.12 1.11 1.07 1.05 1.11 1.07 0.75 0.78 0.74 0.74 1.05 1.02 1.03 1.02 0.81 1.06 0.89 1.18 1.13 1.15 1.15 1.23 1.21 1.18

0.64 0.67 0.54 0.62 0.6 0.58 0.65 0.67 0.67 0.67 0.7 0.74 0.65 0.75 0.64 0.65 0.69 0.62 0.64 0.64 0.62 0.55 0.64 0.61 0.61 0.67 0.6 0.61 0.64 0.67 0.62 0.66 0.61 0.63 0.67 0.62 0.69 0.66 0.7 0.64 0.7 0.67 0.7 0.62 0.6 0.61 0.6 0.62 0.61 0.62

6.84 6.85 6.8 6.7 6.65 6.7 7.28 7.26 7.32 7.22 7.32 6.91 7.12 6.84 7.28 7.26 7.17 7.11 6.94 7.06 7.06 7.23 7.14 7.08 7.23 6.88 6.97 6.99 6.88 7.2 7.33 7.02 6.44 6.32 6.29 6.41 7.1 7.01 7.12 7.09 7.14 7.23 7.06 7.1 7.88 7.19 7.01 6.99 7.06 6.94

<0.1 <0.1 <0.1 <0.1 <0.1 <0.1 0.10 <0.1 <0.1 0.13 <0.1 <0.1 <0.1 0.11 <0.1 <0.1 0.11 0.11 <0.1 <0.1 <0.1 0.12 <0.1 0.12 0.14 0.12 0.13 <0.1 <0.1 <0.1 0.11 <0.1 0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 0.1 <0.1 <0.1 <0.1 0.11 <0.1 0.1 <0.1 0.17 <0.1 <0.1

0.37 0.5 0.38 0.45 0.46 0.45 0.65 0.65 0.67 0.61 0.51 0.6 0.5 0.5 0.7 0.67 0.66 0.74 0.56 0.5 0.44 0.64 0.43 0.41 0.37 0.51 0.41 0.47 0.46 0.62 0.55 0.57 0.74 0.73 0.75 0.67 0.67 0.71 0.73 0.65 0.73 0.64 0.67 0.51 0.40 0.47 0.41 0.41 0.45 0.42

0.57 0.61 0.54 0.61 0.63 0.65 0.66 0.69 0.73 0.73 0.55 0.6 0.51 0.54 0.63 0.6 0.59 0.72 0.65 0.58 0.46 0.42 0.51 0.46 0.54 0.67 0.62 0.59 0.64 0.66 0.65 0.75 0.86 0.86 0.88 0.88 0.68 0.74 0.59 0.65 0.87 0.6 0.79 0.57 0.56 0.69 0.6 0.53 0.54 0.56

RI PT

Mn

<0.2 <0.2 <0.2 0.32 <0.2 0.22 0.33 0.34 0.36 0.28 0.36 0.31 0.41 0.28 0.4 0.24 0.24 0.38 0.33 0.24 0.28 0.22 0.36 0.32 0.18 0.31 0.34 0.29 0.34 0.35 0.34 0.32 0.38 0.52 0.5 0.4 0.32 0.27 0.48 0.27 0.51 0.25 0.44 0.2 0.23 0.21 0.38 0.35 0.23 0.30

SC

Midblue

0.12 0.17 0.13 0.12 0.1 0.17 <0.1 0.16 0.14 0.11 <0.1 <0.1 0.16 0.25 0.16 <0.1 <0.1 0.14 0.11 0.23 0.1 <0.1 <0.1 <0.1 <0.1 0.18 0.11 0.19 0.11 0.11 0.14 0.04 0.13 0.14 0.15 0.18 0.22 0.18 <0.1 0.1 <0.1 0.2 0.1 <0.1 <0.1 <0.1 <0.1 0.23 <0.1 <0.1

M AN U

WC181

66.55 67.36 67.49 67.09 66.49 66.75 66.95 66.96 67.17 67.18 67.75 68.46 68.84 68.36 68 67.56 67.44 67.44 67.13 67.68 68.58 68.49 67.94 68.50 68.60 67.29 67.46 67.59 67.11 66.96 67.01 66.43 63.33 63.35 63.71 62.79 66.66 67.24 67.07 67.08 64.85 67.03 65.00 68.36 68.24 67.61 67.27 67.58 68.04 67.68

TE D

Mn

2.08 2.34 2.20 2.13 2.18 2.04 2.27 2.27 2.24 2.20 2.37 2.39 2.31 2.46 2.26 2.29 2.36 2.26 2.25 2.35 2.40 2.35 2.38 2.35 2.35 2.36 2.37 2.13 2.25 2.26 2.35 2.25 2.18 2.21 2.13 2.13 2.22 2.37 2.34 2.26 2.19 2.27 2.21 2.38 2.27 2.23 2.25 2.32 2.26 2.34

EP

Yellow/ Green

0.48 0.35 0.45 0.44 0.37 0.39 0.53 0.39 0.44 0.44 0.52 0.47 0.50 0.47 0.53 0.47 0.46 0.41 0.51 0.59 0.51 0.47 0.47 0.55 0.47 0.46 0.56 0.51 0.56 0.55 0.51 0.47 0.41 0.44 0.39 0.44 0.54 0.55 0.48 0.52 0.53 0.53 0.48 0.46 0.50 0.55 0.55 0.48 0.51 0.51

AC C

WC61

15.25 15.27 14.89 14.75 14.73 14.76 15.84 15.75 15.90 15.89 16.19 15.76 16.50 15.98 16.04 16.34 16.16 16.24 17.18 17.32 17.50 17.86 17.12 16.81 17.20 16.90 17.15 17.02 17.19 16.44 16.53 16.78 15.45 15.40 15.47 15.58 16.40 16.32 16.48 16.48 15.76 16.22 15.89 16.77 16.22 17.00 17.30 17.18 17.20 17.51

<0.1 <0.1 <0.1 <0.1 <0.1 <0.1 0.11 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 0.1 <0.1 <0.1 <0.1 <0.1 <0.1 0.10 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 0.10 <0.1 <0.1 0.10 <0.1 <0.1 0.31 0.37 0.36 0.33 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 0.1 <0.1 <0.1 <0.1

0.71 0.68 0.35 0.39 0.30 0.36 <0.1 <0.1 0.10 0.16 0.11 0.13 <0.1 0.11 0.01 0.05 0.05 0.11 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 0.10 0.15 0.14 0.11 <0.1 <0.1 <0.1 0.49 0.45 0.45 0.45 0.13 0.16 0.12 0.12 0.11 0.11 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1

<0.1 0.11 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 0.12 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1

0.27 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 0.20 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 0.29 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2

0.30 <0.2 0.33 <0.2 0.24 <0.2 2.05 1.95 1.64 1.60 1.46 1.42 0.74 1.32 1.32 1.34 1.55 1.55 1.44 0.79 0.49 0.20 0.89 0.93 0.55 1.69 1.08 1.14 1.35 1.62 1.37 1.9 5.64 5.70 5.40 6.06 1.87 1.55 1.53 1.73 3.13 1.60 2.85 0.98 0.91 1.06 1.38 0.97 0.93 1.03

4.27 3.39 4.44 4.78 5.81 5.35 1.32 1.47 1.44 1.57 0.89 0.69 0.47 0.71 0.77 1.1 0.94 0.97 0.97 0.69 0.16 0.02 0.77 0.62 0.36 0.72 0.75 1.08 1.19 1.34 1.26 1.48 2.17 1.95 2.01 2.05 1.26 1.14 1.18 1.12 2.38 1.41 2.28 0.54 0.66 0.78 0.68 0.75 0.76 0.61

ACCEPTED MANUSCRIPT

WC65

Pale grey- Sb-Mn blue

WC67

Pale grey- Sb-Mn blue

WC69

Pale grey- Mn blue

WC17

Emerald green

PA

WC18

Emerald (trans) green

Mn

WC13

Turqu’se

Sb-Mn

WC12

Turqu’se

Sb-Mn

Cake

Turqu’se

Sb-Mn

WC70

Deep

Sb

Mn

<0.1 <0.1 0.1 <0.1 0.16 0.24 0.17 0.16 0.19 0.15 <0.1 0.17 0.14 0.13 <0.1 0.16 <0.1 0.13 <0.1 <0.1 0.17 <0.1 <0.1 0.14 0.22 0.22 <0.1 0.12 <0.1 0.46 0.47 0.45 0.44 0.15 <0.1 <0.1 0.14 <0.1 <0.1 0.13 <0.1 <0.1 <0.1 <0.1 0.11 0.14 <0.1 <0.1 <0.1 <0.1

0.38 <0.2 <0.2 0.27 0.33 <0.2 0.28 0.28 <0.2 0.31 0.34 0.30 0.36 0.58 0.52 0.59 0.46 0.50 0.65 0.52 0.57 0.57 0.51 0.47 0.48 0.37 0.51 0.49 0.51 0.23 0.22 0.27 <0.2 0.26 <0.2 <0.2 0.22 0.50 0.43 0.30 0.36 0.64 0.62 0.60 0.51 0.42 0.38 0.35 0.30 0.41

1.07 1.21 1.26 1.26 1.11 1.21 1.18 1.18 1.23 1.12 1.15 1.15 1.11 1.03 0.96 0.99 1.1 0.95 0.98 0.99 0.96 1.01 0.97 0.96 0.94 0.93 0.91 0.92 0.88 1.25 1.19 1.23 1.2 1.24 1.23 1.23 1.2 1.59 1.56 1.55 1.54 1.03 1.05 1.09 1.02 1.54 1.53 1.59 1.51 1.37

0.61 0.67 0.64 0.61 0.62 0.63 0.54 0.55 0.57 0.68 0.62 0.66 0.66 0.66 0.71 0.63 0.69 0.64 0.58 0.61 0.63 0.61 0.67 0.61 0.59 0.66 0.65 0.64 0.63 1.08 1.14 1.1 1.11 0.68 0.64 0.73 0.65 0.59 0.54 0.58 0.57 0.63 0.60 0.59 0.62 0.61 0.63 0.58 0.66 0.47

7.5 7.86 7.82 7.57 7.4 7.68 7.67 7.73 7.63 6.94 7.03 7.04 7.06 6.13 6.39 6.08 6.03 5.92 5.98 5.94 5.9 5.88 5.97 5.97 5.95 6.58 6.46 6.41 6.56 6.84 6.85 6.92 6.82 7.04 7.2 7.21 7.17 5.67 5.72 5.71 5.63 5.11 5.12 5.18 5.18 5.71 5.77 5.78 5.65 5.63

<0.1 <0.1 <0.1 0.13 <0.1 0.13 <0.1 <0.1 0.13 <0.1 <0.1 0.11 <0.1 0.13 <0.1 <0.1 0.13 0.10 0.17 0.10 <0.1 0.11 0.11 0.14 0.11 0.05 0.15 0.07 0.07 0.12 0.13 0.12 0.11 0.13 0.17 0.11 0.14 0.14 0.15 <0.1 0.16 0.11 0.10 <0.1 0.11 0.16 0.17 0.13 0.14 0.11

0.66 0.48 0.39 0.38 0.64 0.47 0.47 0.51 0.47 0.71 0.72 0.65 0.63 0.3 0.27 0.3 0.27 0.21 0.24 0.22 0.26 0.26 0.25 0.25 0.24 0.4 0.48 0.49 0.48 0.95 0.91 0.91 0.94 0.38 0.41 0.37 0.37 0.22 0.24 0.20 0.20 0.03 0.12 0.10 0.10 0.24 0.20 0.16 0.19 <0.1

0.62 0.35 0.42 0.46 0.59 0.51 0.43 0.44 0.47 0.72 0.6 0.64 0.56 0.68 0.66 0.68 0.73 0.65 0.69 0.66 0.71 0.65 0.63 0.66 0.69 0.61 0.63 0.65 0.6 0.73 0.66 0.68 0.62 2.59 2.46 2.58 2.61 0.54 0.59 0.55 0.54 0.54 0.53 0.53 0.52 0.54 0.43 0.56 0.61

RI PT

Midblue

67.92 69.39 69.89 69.31 67.62 69.43 69.44 69.12 69.21 66.78 66.92 67.19 66.94 65.91 66.07 66.18 65.6 65.78 65.40 65.29 65.67 65.55 65.70 65.79 65.77 66.25 65.94 65.83 66.15 65.3 65.82 65.78 65.74 67.57 67.57 67.93 67.46 65.82 65.53 65.52 65.75 64.03 64.53 64.11 64.14 65.56 65.72 65.53 65.65 69.49

SC

Cake

2.31 2.47 2.37 2.42 2.30 2.48 2.42 2.38 2.39 2.38 2.18 2.19 2.24 2.25 2.31 2.25 2.31 2.31 2.27 2.19 2.25 2.27 2.18 2.23 2.23 2.46 2.35 2.26 2.30 2.20 2.10 2.17 2.19 2.35 2.27 2.43 2.39 2.07 2.10 2.14 2.09 2.12 2.17 2.13 1.98 2.04 2.14 2.21 2.11 1.85

M AN U

Pale blue Mn cloudy

0.53 0.49 0.49 0.42 0.40 0.46 0.50 0.50 0.46 0.45 0.51 0.50 0.54 0.48 0.48 0.59 0.54 0.54 0.50 0.60 0.63 0.67 0.58 0.52 0.56 0.42 0.50 0.52 0.45 1.23 1.20 1.28 1.27 0.54 0.49 0.45 0.59 0.59 0.51 0.50 0.51 0.44 0.42 0.37 0.45 0.54 0.51 0.53 0.58 0.38

TE D

WC74

15.21 15.63 15.23 15.89 15.18 15.90 15.99 16.06 16.05 16.47 16.25 16.44 16.39 17.79 17.74 17.70 17.95 18.49 18.48 18.39 18.26 18.47 18.57 18.42 18.57 16.99 17.06 17.05 17.10 16.42 16.41 16.47 16.58 16.83 16.54 16.51 16.56 18.72 19.01 19.33 19.13 18.63 18.37 18.15 18.34 19.24 19.02 19.20 19.04 18.31

EP

Pale blue Mn cloudy

AC C

WC78

<0.1 <0.1 <0.1 <0.1 0.14 <0.1 0.11 <0.1 <0.1 0.13 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 0.1

0.12 <0.1 <0.1 <0.1 0.10 <0.1 0.17 <0.1 <0.1 0.10 0.14 0.12 0.17 <0.1 0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 1.92 1.98 1.94 2.01 <0.1 <0.1 <0.1 <0.1 0.90 0.99 0.97 1.00 2.76 2.74 2.80 2.84 0.93 0.99 0.94 1.04 <0.1

<0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 0.12 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 0.14 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1

<0.2 0.23 0.3 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 0.3 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 0.34 0.32 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2

1.56 0.53 0.42 0.68 1.81 <0.3 <0.3 0.44 0.40 1.69 1.83 1.52 1.81 3.60 3.33 3.20 3.57 3.34 3.47 3.68 3.52 3.53 3.48 3.26 3.20 3.80 4.04 4.12 3.96 0.51 0.22 0.07 0.03 0.11 0.46 <0.3 0.45 2.26 2.32 2.29 2.25 3.45 3.29 3.65 3.88 2.03 2.08 2.06 2.01 1.01

1.31 0.26 0.34 0.43 1.49 0.33 0.36 0.42 0.37 1.27 1.33 1.22 1.12 0.23 0.22 0.37 0.44 0.26 0.37 0.26 0.25 0.17 0.21 0.34 0.36 0.15 0.15 0.3 0.12 0.36 0.32 0.39 0.57 0.05 0.17 0.15 0 0.3 0.21 0.15 0.13 0.23 0.22 0.34 0.11 0.28 0.23 0.29 0.36 0.2

ACCEPTED MANUSCRIPT

<0.1 <0.1 0.10 <0.1

0.46 0.45 0.44 0.35

1.42 1.34 1.44 1.43

0.56 0.55 0.62 0.49

5.50 5.59 5.54 5.67

0.16 0.10 <0.1 <0.1

<0.1 <0.1 <0.1 <0.1

0.64 0.56 0.64 0.67

SC

RI PT

68.84 68.86 68.63 68.63

M AN U

1.83 1.78 1.77 1.85

TE D

0.34 0.31 0.36 0.32

EP

18.36 18.59 18.54 18.71

AC C

(trans) blue

<0.1 <0.1 <0.1 0.12

0.16 0.15 0.10 0.14

<0.1 <0.1 <0.1 <0.1

0.23 <0.2 0.29 <0.2

1.16 1.09 0.98 1.20

0.1 0.28 0.38 0.29

ACCEPTED MANUSCRIPT

12 15 18

Co 16307 39142 117867 40110 41141 15862 82853 104803 63066 2000 8115 4521 3659 11709 11930 9374 7235 10295 12857 18023 808 1545 1774 1769 265

Cu 34 12 7 41 15 11 8 6 9 383 167 180 145 397 422 317 226 411 544 2358 120 17 3 18 8

V 13980 19955 12074 3316 126 1217 5628 68 136 485 259 280 383 903 974 722 527 615 789 3460 309 7528 20830 8094 63

Cr 31.8 17 21.8 16 13.1 15.8 14.8 17.4 16 4 14.8 17.1 15.6 16.6 16.6 17 13.9 14.8 16 8.9 16.8 12.1 10.1 13.1 15.1

Ni 18.6 12.4 13 12.9 10.9 10.7 13.1 14.7 13.6 7.3 12.8 11.1 12.3 11.9 12.3 11.4 9.9 11.2 12 13.8 11.7 11.4 10.3 12.8 11.9

Zn 24.2 17.5 16.5 11.3 11.4 10.6 9.9 9.6 10.5 12.5 14 15.3 13.2 22.4 24.1 19.9 17.1 22.7 27.9 91.7 10.6 7.8 7.8 11.9 9.7

As 447 138 34 88 265 27 23 24 24 24 26 17 19 28 34 27 29 24 24 24 27 31 108 34 22

Rb 14.1 31 32.4 54.9 15.7 13.7 23.3 118.2 15.9 15.8 15.5 5.8 4.4 14.7 14 13.5 10.2 10.9 14.5 34.7 29 17.5 50 18.2 7.1

Sr 8.4 10.3 12.4 8 7.7 6.8 9.6 10.1 10.5 4.8 10.2 7 7.9 8.5 9.7 8.7 6.9 8.3 8.4 7.1 9.4 8.1 10.6 8.6 9.6

Y 577 419 439 397 400 394 363 331 326 393 453 449 452 444 452 444 369 420 448 361 418 382 317 389 417

Zr 6.4 7 7.2 5.5 6.5 6 6.2 5.9 5.7 4.8 7.2 7.1 7.2 6.7 6.9 6.9 5.4 6.4 6.5 5.8 6.9 6.4 5.3 6.4 6.9

Nb 7 26 42 7 23 7 35 36 47 26 28 22 19 92 44 44 31 44 42 8 54 65 158 70 27

Mo 0.9 1.3 1.6 0.9 1.1 1 1.9 2.1 1.9 1.1 1.6 1.9 1.4 1.6 1.6 1.5 1.3 1.5 1.4 1 2 2.4 1.8 <0.4 2.3 1.7

Ag Ba 3.3 5.9 1.9 12.9 2.4 10.4 1.5 5.3 1.4 9 1.8 2.5 1.2 6.5 0.9 7.4 1.4 5.2 0.2 <0.8 1.3 <0.8 3.9 11.7 3 7.6 2.4 1.5 2.5 4.2 2.5 3.5 2.2 2.5 1.9 1.8 2.1 1.8 1.3 2.3 1.3 <0.8 0.6 1.7 9 0.7 3.6 1.4 <0.8

La 307 238 271 211 260 240 213 183 203 141 257 285 283 268 259 257 230 250 253 227 239 184 202 266 256

Ce 7 7 7.3 5.5 6.2 6 6.4 6.8 6 4.9 6.7 6.8 6.4 6.7 6.6 6.1 5.5 6.2 6.2 5.3 7 6.8 6.5 7.5 6.9

RI PT

Pb 405 3056 5849 2000 2059 1226 7050 7341 6118 4035 8170 2827 2472 11234 11374 9630 7779 7035 8166 18038 22890 12425 14673 12053 1919

SC

Cake

Sb 325 1278 814 255 691 78 671 429 325 24 25 6 14 60 65 55 43 26 19 117 15 106 506 88 18

M AN U

88 102 108 166 176 179 69

Sn 889 388 415 502 320 369 524 695 608 220 369 329 311 419 366 366 293 344 330 212 430 667 529 691 426

TE D

Cake

Colour P Ti Red 4739 Green 473 Green 494 Green /yellow 1404 Yellow green 667 Yellow green 971 Yellow 592 Yellow 375 Yellow (chips) 431 Deep blue (trans) 71 Pale blue 595 Pale cloudy blue 631 Pale cloudy blue 502 Mid-blue 716 Mid-blue (trans) 705 Mid-blue (trans) 645 Mid-blue (trans) 576 Mid-blue 757 Mid-blue 581 Mid-blue 592 Pale grey-blue 511 Turquoise 384 Turquoise 438 Turquoise 431 Emerald (trans) 548

EP

21 3 6 10 30 35 51 62 64 19 66 74 78

AC C

Sample

Nd 13.8 12.4 12.1 10.2 11.2 10.9 12.5 12.6 11.6 9.4 12.6 12.1 12.1 11.9 11.9 11.1 10.1 10.9 11.1 8.6 12.5 12.7 11.7 13.2 13.1

Hf 6.5 7.4 6.6 5.4 5.9 5.5 6.8 5.7 5.5 4.5 6.6 6.4 5.9 6.4 6.5 6.4 5.6 6.2 5.9 4.6 6.4 6.4 6 6.7 6.9

0.1 2.5 1.1 0.1 0.4 0.2 0.7 0.6 1.1 0.7 0.7 0.8 0.3 1.2 1.3 1.3 0.8 1.3 1.3 0.2 1.4 1.7 1.4 1.3 0.7

Au <0.3 <0.3 <0.3 <0.3 <0.3 <0.3 <0.3 <0.3 <0.3 <0.3 <0.3

Tl

2 1.8 <0.3 0.8 0.7 0.7 0.5 0.5 <0.3 <0.3 <0.3 1.7 <0.3 <0.3

Bi 7 17.6 50 16.9 17.6 6.8 34.8 42.5 25.9 0.8 3.4 2.2 1.8 4.9 5.2 4.1 3.1 4.4 5.5 7.4 0.4 0.6 0.7 0.7 0.1

Th 1 1.1 1 1.8 0.8 0.9 0.9 0.2 0.6

<0.04 0.1 <0.04 0.1 0.4 0.6 0.6 0.4 0.2 0.2 0.2 <0.04 <0.04 0.2 <0.04 <0.04

Li 0.3 2.1 1.6 0.3 0.7 0.2 1 1.1 1.1 0.4 0.5 1.5 1.1 1 1.5 1.5 0.9 1.5 1.2 0.1 1.3 1.3 1.5 1.1 0.7

Be 5.7 4.1 6.4 4.6 2.9 4.3 4.6 5 5 2 5.8 5 5.3 4.8 4.2 4.7 3.9 5 4.4 2.3 2.8 4.8 3.9 4.5 4.5

0.3 0.9 <0.1 0.3 0.3 0.2 0.2 0.2 0.2 <0.1 0.4 0.6 0.5 0.2 0.4 0.2 <0.1 0.3 0.4 <0.1 0.4 0.3 <0.1 0.3 0.2