Romano-British wall paintings: Raman spectroscopic analysis of fragments from two urban sites of early military colonisation

Spectrochimica Acta Part A 73 (2009) 553–560

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Romano-British wall paintings: Raman spectroscopic analysis of fragments from two urban sites of early military colonisation H.G.M. Edwards a,∗ , P.S. Middleton b , M.D. Hargreaves a a b

Division of Chemical and Forensic Sciences, School of Life Sciences, University of Bradford, Bradford BD7 1DP, UK Diocese of Peterborough, The Palace, Peterborough PE1 1YR, UK

a r t i c l e

i n f o

Article history: Received 23 June 2008 Received in revised form 24 September 2008 Accepted 23 October 2008 Keywords: Roman pigments Archaeological analysis Wall paintings Raman spectroscopy

a b s t r a c t Raman spectroscopic analyses of 1st century AD Romano-British villa wall-painting fragments from two important military and early urban centres at Colchester and Lincoln have demonstrated some interesting contrasts in technique and palette usage. Colchester, the earliest fortified settlement, developed a sophisticated painting and craft industry compared with Lincoln in the assimilation of novel substrate preparation ideas and pigment adoption. The earliest use of the rather rare purple mineral pigment, caput mortuum, hitherto reported in only a few Roman villas elsewhere in mainland Europe, is in evidence in this early phase settlement and the use of gypsum as a special ground preparation agent as an additive to the more common limewash putty to enhance the effect of the use of lazurite as a pigment is worthy of note in this context. Otherwise, the pigments are seen to be those that are quite normally encountered in Roman villas, namely, haematite, goethite, terre verte, and carbon. The results of this study indicate that at Colchester there was a continued development in technique into the colonial phase compared with a stagnation in Lincoln; these scientific results have created a stimulus for further historical research into pigment and techniques development for wall paintings at the fringe of the Roman Empire in the 1st–3rd Centuries AD. © 2008 Elsevier B.V. All rights reserved.

1. Introduction The Roman invasion of Britain began with a rapid military campaign to secure the southeast corner of the island and the establishment of a major legionary military base at Colchester (Camulodunum). Following the assimilation of the tribes of this area, by ca. 50 AD, the legions had been moved forward to bases in newly won territories, such as Lincoln. As the military command moved on, so the Roman administration initiated new civilian settlements, first at Colchester and then, in due course, at Lincoln and elsewhere, to serve as a dependable example to the local tribal communities. Such colonies, whose first residents were retired military personnel, were intended to provide stability in the new province and a focus for local tribes to become familiar with the administrative structures and lifestyles appropriate to the new order. One of the earliest indigenous communities to follow the lead of the planted colony at Colchester was the centre of the tribal group immediately to the west, modern day St. Albans (Verulamium). Resentment against the conquest, however, built up and boiled over in 60–61 AD with a major uprising known as the Boudican

∗ Corresponding author. E-mail address: [email protected] (H.G.M. Edwards). 1386-1425/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2008.10.027

Revolt. This was speedily overcome, but at the cost of massive destruction in the existing Romanized communities. Archaeologically, this has been fortuitous, since it created identifiable horizons which can be securely dated. It is therefore possible to trace three distinct phases in the early development of these earliest urban settlements: an initial military phase, followed by the early colonial settlement and then, in the case of Colchester, the rebuilding of the colony following the Boudican destruction. As the urban settlement of southern Britain became established during the later 1st century AD, so the rural development seems to have followed the tastes and techniques pioneered in the towns, giving rise to the pattern of villa farmstead settlement so familiar in all descriptions of Roman Britain. In a series of recent studies, the colour palette used by the Romano-British villa owners of the Nene Valley in Northamptonshire during the 2nd–4th centuries AD has been analysed [1–4]. The approach adopted in these studies has been to focus on the techniques of painting and the pigments used, rather than the traditional art-historical approach. Raman spectroscopy has played an important role in the characterisation of the pigments used by the artists and in the identification of the techniques used in the preparation of the wall substrates. The emerging picture has been of a craft skill, which used a minimal palette of colours with great ingenuity in order to offer a

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range of effects to the landowners who commissioned the work. The craft workers involved were evidently versed in a common body of knowledge of painting techniques, which are summarised by classical authors, such as Pliny the Elder [5] and Vitruvius [6], and they seem to have blended that knowledge with a developed local and regional awareness of materials. In order to compare these results from rural Roman Britain with samples from an urban context, the opportunity was taken to carry out a preliminary feasibility study [7] of a set of wall plaster fragments from the earliest Roman military colony of Colchester. This study has now been significantly extended in this paper to include samples from Roman structures built in the contemporary military colony [8] of Lincoln and the combined results from these studies are reported here. 2. Experimental 2.1. Samples Samples from both the Colchester and Lincoln sites were selected to maximise the colour palette represented. All specimens were analysed, but in the tables which follow for simplicity the contexts are reported rather than the individual analyses of the relatively large numbers of fragments studied; in addition, each fragment studied comprised an accumulation of data from several points to ensure that a representative analysis was obtained of the pigment and substrate composition. Three sites in Colchester, yielding 58 samples, were selected for study. Each is located within the military fortress of the XXth Legion and the later civilian colony and provided a sequence of deposits which could be firmly dated to three phases as outlined in Section 1: • military, AD 43–49 (6 reported samples from 2 contexts); • colony, AD 49–60/61 (32 reported samples from 6 contexts); • post-Boudican colony, AD 60/61 – early 2nd century (20 reported samples from 9 contexts). The security of the archaeological contexts enables us to track the development of pigment use through the first hundred years of the settlement at Colchester. It was anticipated that Colchester, as the first colony and first capital of the newly formed Roman province, might exhibit a more refined and richer range of techniques than the villa sites that have been studied hitherto. We were also interested to explore the similarities in technique as a possible source of ideas, materials and expertise for the methods that were employed in the later villa sites. A total of 9 sites, yielding 45 fragments of wall plaster, were sampled for the data set from Lincoln. These sites were located throughout the Neronian period military fortress base of the IXth Legion, which became the focus of the first colony, and the later Lower Colony. As at Colchester, accurate stratigraphical and contextual dating allows us to apportion the samples into three chronological phases: • military, ca. AD 50 – ca. AD 75 (19 reported samples from 5 contexts); • early colony, ca. AD 85 – early 2nd century AD (17 reported samples from 4 contexts); • Later colony, mid–late 2nd century AD (9 reported samples from 2 contexts). Once again, the firm chronological framework allows us to address questions of developments over time. The Lincoln sample

set can also be put alongside that from Colchester in order to consider the similarities and differences between high-status urban sites, both having been prestigious Roman colonial settlements. 2.2. Raman spectroscopy Raman spectra were mostly recorded using a Bruker IFS 66/FRA 106 instrument (Ettlingen, Germany) with an Nd3+ /YAG solid state laser operating at 1064 nm, with a spectral footprint of approximately 100 ␮m and a liquid nitrogen cooled InGaAs detector. Spectra were accumulated over 2000 scans at a spectral resolution of 4 cm−1 to improve signal-to-noise ratios and each specimen was interrogated at several positions to ensure that a representative conclusion could be made from the heterogeneous materials being analysed. The spectral wavenumber range was typically 4000–80 cm−1 . Wavenumbers of sharp Raman bands are correct to better than ±1 cm−1 . A daily interferometer function check is required and is achieved by recording the Raman spectrum of sulphur. Spectra were not corrected for instrument response. The spectrometer was controlled by PC with instrument control software (Bruker Opus NT version 3). As the specimens were in the form of plaster fragments, it was possible to examine the methodology of substrate preparation and techniques of pigment application. Mineral pigments were characterised from spectra obtained in our previous studies and from comparison with literature databases. Raman spectra were also obtained using a Renishaw InVia Reflex spectrometer (Wotton-under-Edge, UK), operating with a high power Renishaw NIR diode laser emitting at 785 nm, a Renishaw HeNe emitting at 633 nm and a Laser Physics Reliant 150 M emitting at 514.5 and 488 nm, utilising a CCD detector (400 × 575 pixels) thermoelectrically cooled down to −70 ◦ C. Coupled to a Lieca DMLM microscope using 50× (NA 0.75), 20× (NA 0.40), and 5× (NA 0.12) microscope objectives which provided a spectral footprint of approximately 2–20 ␮m. The diffraction gratings of 1200 lines/mm (NIR) and 2400 lines/mm (UV–vis) give the spectral range 3200–100 cm−1 with a spectral resolution of 2 cm−1 . Daily calibration of the wavenumber axis is achieved by recording the Raman spectrum of a silicon wafer (1 accumulation, 10 s) in static mode. If necessary, an offset correction is performed to ensure that the position of the silicon band is 520.5 ± 0.1 cm−1 . Spectra were not corrected for instrument response. The spectrometer was controlled by PC with instrument control software (Renishaw WiRE 2 Service Pack 9). The excitation wavelength was selected to be most appropriate for the coloured pigments involved; all samples except the blue and green pigments were found to be most amenable to near infrared excitation at 785 and 1064 nm and for the former specimens 488 and 514.5 nm excitation was used. However, the 1064 nm excitation was found to be useful especially for analysis of the limewash ground samples which gave no signals with the visible excitation wavelengths. The 633 nm excitation is useful for the analysis of the red, black, grey and yellow pigments. 3. Results 3.1. Colchester As noted above, only six fragments of wall plaster from two contexts were available for spectroscopic analysis from the earliest, military phase of occupation [Table 1]. All but one were coloured cream or white; these being a limewash putty/calcite mixture as used in the substrate preparation and for which an example is shown in Fig. 1. The sole exception has a mixture of yellow, pink and, notably, purple colours as well as white; although this spec-

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Table 1 Legionary military phase, Colchester. Sample

Colour description

Analysis

HS 2160

Cream

Calcite, limewash

HS 2976

Purple White Pink Yellow

Caput mortuum, haematite, goethite

Comments

Biodeterioration

HS: Head Street.

Fig. 1. FT-Raman spectrum of limewash putty substrate, 1064 nm excitation, showing the broad feature centred at 790 cm−1 arising from the calcium hydroxide/calcium oxide component and the bands at 1085, 710, 280 and 154 cm−1 which are ascribed to calcite from conversion of the limewash on reaction with atmospheric carbon dioxide; 100–1800 cm−1 range, 4 cm−1 spectral resolution. Specimen Colchester, HS2160.

imen exhibited significant fluorescence emission generally, which is often encountered in the analysis of archaeological specimens recovered from depositional environments, it was possible to locate several regions of interest when excited using longer laser wavelengths at 785 or 1064 nm. In particular, the characterisation of the purple iron oxide mineral, caput mortuum, as demonstrated in Fig. 2 was an important analytical result since this pigment has been rarely found in Roman wall plaster decoration. Other pigments determined in this sample were calcite and a haematite/goethite mixture (Fig. 3). In some sample points the presence of cyanobacte-

Fig. 2. Raman spectrum of caput mortuum, a purple mineral form of haematite, 633 nm excitation, 2 cm−1 spectral resolution, 100–1800 cm−1 range. Specimen Colchester HS2976.

Fig. 3. Raman spectrum of a haematite/goethite mixture, 633 nm excitation, range 100–1800 cm−1 , 2 cm−1 spectral resolution. The mineral pigment bands lie in the 650–200 cm−1 region and the broad bands in the region between 1200 and 1600 cm−1 can be attributed to a degraded biological component probably arising from the depositional environment of the specimen.

rial colonisation could be detected from Raman bands in the region of 1300–1600 cm−1 and from CH bands near 3000 cm−1 which could explain the significant background fluorescence emission from this specimen. The first colonial phase of activity yielded 32 fragments for analysis, 10 of which were plain white, without colour variation [Table 2]. The remaining samples showed a wider range of colour than that exhibited in the military phase, with six distinct colours, as compared with four (taking cream and white as one colour). Purple was again present, again confirmed as the mineral caput mortuum (see discussion, below). A surprising result was the analytical identification of the blue pigment as lazurite, a rare and expensive pigment [Fig. 4] which was found unusually

Fig. 4. Raman spectrum of lazurite with a trace of gypsum, 488 nm excitation, range 200–1800 cm−1 , spectral resolution 2 cm−1 .

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Table 2 Early colony, Colchester. Sample

Colour description

Analysis

Comments

White White Blue

Gypsum, calcite, limewash, quartz Calcite, gypsum Lazurite, calcite, gypsum

Substratum

HS 2071

H 2000.98. 62(L29)

Red Black Purple Green Blue

Haematite, calcite, limewash Carbon, limewash Calcite, haematite, limewash Green earth, calcite No result

H 2000.98 70 (L31)

Green

Green Earth, calcite

H 2000.98 71 (L30)

Red Black

Haematite, gypsum, calcite Carbon

HS 2000.41 1294 HS 2000.41 1840

White White

Calcite, limewash Calcite, limewash

Caput mortuum Fluorescence

H: Harpers; HS: Head Street.

increase in the range of observed colours, from six to nine different pigments being identified, including again the rare caput mortuum and a green earth (terre verte, viridian). A pale blue specimen area (GBS84.A1254) failed to yield a spectrum; the absence of bands of lazurite from this specimen could possibly be indicative of the use of Egyptian blue in this context from which a weaker spectrum is expected. Limewash putty was encountered in all three phases as the most common substrate on which pigments were applied. One site, Head Street, yielded evidence of a special wall preparation, using gypsum as the substrate which seems to have provided a finer, whiter finish as a base for the use of the rare pigment, lazurite; the only other use of this gypsum additive in the whole sample set studied here is found with a special highly crystalline form of haematite as described above. Fig. 5. Raman spectrum of highly crystalline haematite in admixture with gypsum, 633 nm excitation, range 100–1800 cm−1 , spectral resolution 2 cm−1 Specimen Colchester H2000.98.41(L30).

with gypsum and more commonly a limewash substrate. Gypsum was not seen elsewhere in the sample set, except for specimen H2000.98.41(L30), which analysed as a very crystalline and pure form of haematite (Fig. 5). The later colonial phase sample set, dated to the post-Boudican reconstruction at Colchester, numbered twenty samples from nine different contexts [Table 3]. Only two fragments were simply white or cream in colour, all the others having a range of pigments used in association. Light blue was encountered and there was a further

3.2. Lincoln Nineteen samples from the earliest military phase were analysed and revealed a near uniform treatment with limewash putty substrate and white or cream pigmentation [Table 4]. In only two instances was a colour introduced, in both cases, red. Traces of biodeterioration in samples from The Lawn probably relate to the disposal of the deposit (the fragments were excavated from a probable rubbish pit), rather than to the use of the structure from which they came. One sample, W73, showed evidence of significant localised carbon deposits on the surface of the white plaster, which we can attribute to fire damage. In this set of samples, especially specimen LH84.AA33, some significant biodeterioration was

Table 3 Later colony, Colchester. Phase

Sample

Colour description

Analysis

GBS84.A1254 GBS84.A1262 GBS84.A2258

Light blue Yellow Black Red White Grey Yellow Red Green Aquamarine Yellow Red/purple Green Red/purple Dark red/purple Black

Calcite, goethite, limewash Carbon Haematite, calcite Calcite Carbon Calcite Goethite Haematite, calcite, limewash Green earth Goethite Limewash, calcite, haematite No result Haematite, Quartz, limewash, calcium carbonate Calcite, haematite Carbon

GBS84.A2297 HS.1062 Post-Boudican rebuilding HS.1151 HS.1300 HS.1819 HS.2649 GBS: Gilberd School Site; HS: Head Street.

Comments

Substratum

Caput mortuum Caput mortuum Caput mortuum

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Table 4 Legionary military phase, Lincoln. Sample

Colour description

Analysis

Comment

EB80.168,229

Calcium carbonate, quartz, limewash putty; haematite

Haematite pronounced spectrum in 168; trace in 229

W73 LH84.AA33

Cream ground (168,229), with red spots (168) White White

Calcium carbonate, carbon, quartz, limewash putty Calcium carbonate, limewash putty

Carbon represents traces of soot Peak at 2800, probably organic in origin, attributable to biodeterioration

LH84.AA45 SP72.CEJ, CBR SP72.BWL WB76.AJ WB76.AQ

White White Red, white White White

Calcium carbonate Calcium carbonate, quartz, limewash putty Haematite Calcium carbonate, limewash putty Calcium carbonate, quartz, limewash putty Calcium carbonate

No limewash putty

EB: East Bight; LH: The Lawn; SP: St. Paul in the Bail; W73 Westgate; WB76 West Bight.

Table 5 Early colony, Lincoln. Sample

Colour description

Analysis

Comments

CL85

Cream Green

Calcite, limewash No result

Fluorescence

SH74

Black Cream Green Red, dark red White

Carbon Calcite, haematite No result Haematite, carbon Calcite

SP72

Black Cream Green Red White Yellow

Carbon Calcite, haematite Green earth Haematite Calcite Goethite

WB76.AH

White

Calcite

Peak at 2800, probably organic in origin, attributable to biodeterioration

CL85: Chapel Lane; SH74: Steep Hill; SP72: St. Paul in the Bail; WB76: West Bight.

noticed which could be attributed to degradation in the depositional environment. The 17 wall plaster samples from the early colony phase at Lincoln reveal a more developed palette of colours, with 5 different pigments represented [Table 5] – black, cream/white, green, red and yellow. All the pigments used are common minerals. The standard limewash putty wall preparation was encountered, although perhaps rather surprisingly it does not always appear to have been used, which suggests a distinctly “rough and ready” approach to the internal decoration being adopted in these cases. From the later colony, two sites were available for sampling and a total of nine fragments were analysed (Table 6). These revealed a limited palette of five colours – cream/white, green, pink, purple and red/dark red. As in the first colonial phase, the pigments used were commonly available and no distinguishing feature in the techniques applied is evident.

4. Discussion The overall range of colours encountered in the sample set from Colchester is not in itself unusual but an interesting feature of the results is the increasing range of colours in each of the three chronological phases [Table 7]. This could be taken as evidence of increasing prosperity and the shift from military to civilian occupation within the settlement. In these circumstances there might have been greater scope for individuals to express their personal tastes in decoration, as compared to the restrictions that were imposed during the more controlled military phase. That the situation is rather complex is suggested by the presence of pink, purple and yellow colours in the samples from the military phase. Given that this sample set is so small, the presence of coloured material is perhaps even more significant. Purple, in particular, was a high status colour in the Roman world, drawing on elite Republican and, of course, later Imperial associations.

Table 6 Later colony, Lincoln. Sample

Colour description

Analysis

BE73

Pink Red White

Haematite, calcium carbonate Haematite Calcite, quartz, limewash putty

WB80

Cream Dark red Green Purple

Calcite, carbon, limewash putty Haematite, carbon No result Haematite

BE73: Broadgate East; WB80: West Bight.

Comment

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Table 7 Pigment use at Colchester. Colour Aquamarine Black Blue Green Grey Pink Purple Red White/cream Yellow

Military phase

+ + *(calcite, limewash) +

Early colony

Later colony

*(carbon) *(lazurite with calcite,limewash, gypsum) *(green earth, clacite)

+ *(carbon) + *(green earth) *(calcite, carbon)

*(caput mortuum) *(haematite, calcite) *(calcite, limewash, gypsum)

*(caput mortuum) *(haematite, calcite) *(calcite, limewash) *(goethite, calcite)

(*) Sample analysed; (+) visual identification, no result on analysis.

Pliny [5] records the problems encountered with the isolation of the organic purple pigment, produced by crushing the shells of the marine shellfish, murex, and the even more problematic issue of preserving the intensity of what was even then appreciated as a highly fugitive colour. For these reasons, purple was a very expensive pigment and Pliny lists it as one of the few that were explicitly identified as incurring an additional cost to the patron (Pliny [9]). There is growing evidence that special efforts were made by Romano-British artists, in common with their Roman colleagues, to produce an inorganic substitute for the expensive organic purple dye. This has been identified [10] as a fine-grained, haematitebased pigment recipe, known as caput mortuum. The samples of purple pigment from the Colchester military phase have yielded clear confirmation of the use of this pigment in Romano-British wall decoration there; the mere presence of such a pigment in these sites is significant and lends weight to the suggestion that the finds are likely to represent a high status structure. Bearat [11] has commented on the rarity of caput mortuum encountered in wall paintings of the Roman Empire; for over 500 known Roman villa sites with wall paintings in Europe in only about 12 has caput mortuum been identified. An historically significant addition to this list can now be appended with the inclusion of the early RomanoBritish structures in Colchester. In a consideration of the pigment palette of the first colonial phase, we note an increasing variety of pigments used, a confirmation of the use of caput mortuum and, even more striking, the presence of an unusual technique involving gypsum plaster usage and the presence of the exotic pigment, lazurite. The use of gypsum as a wall preparation is rare in the pre-Medieval period, only becoming a standard constituent of substrate preparation for frescoes and wall painting in Renaissance Europe. The normal substrate in the Roman period, especially in the north-western provinces, appears to have been a limewash putty [6]. This limewash putty is manufactured according to ancient recipes [5,6] by the calcining of limestone, treatment of the resultant oxide and hydroxide with limited water and storage underground for several weeks to attain its putty-like consistency before use in wall preparation, when its surface is converted into calcite [12]. Interestingly, limewash is confirmed by our analysis in all three sets of samples from Colchester as

the dominant preparation, so the presence of gypsum here should be regarded as particularly significant. Indeed, its use in association with lazurite, and incidentally along with a particularly crystalline sample of haematite, will certainly have been a matter of choice, probably reflecting the importance attached to the use of the rare mineral pigments. The effect of a gypsum wall preparation would have been to enhance the surface quality of the substrate through its fine particle size. Such an effect is discussed in the ancient sources (Vitruvius [13]) where marble dust is recommended for this enhancement as the best possible preparation. Recent work on villa wall paintings in both Roman Britain and northern Italy has demonstrated the achievement of similar effects by the addition of fine grade clays [5,14]. We can therefore conclude that the use of gypsum in the earliest colonial phase at Colchester was precisely to provide the fine, burnished finish, much sought after in the finest quality wall paintings and designed, in this case, to show off the expensive pigment, lazurite. Lazurite was a rare and expensive pigment, first known in the Roman world from sources in Afghanistan and accessed through the eastern desert routes at extremely high prices, as recorded by Pliny the Elder [5]. Although prices may have fallen with discoveries in Spain and, possibly Campania (although, curiously, these are not explicitly mentioned by Pliny), lazurite remained a luxury item. For this reason, it seems, the vast majority of blue wall painting elements in centres like Pompeii and more generally in the western provinces of the empire were fashioned with the artificially manufactured Egyptian Blue (Augusti [15], Bearat [16]). The later colonial phase samples reveal a developing awareness and interest in colour amongst the colonial settlers at Colchester. There appears to be a significant increase in the palette of colours, from six in the early colony, to nine, although the small sample size must urge caution at this stage of the research. Nevertheless, it is interesting to note that, alongside this developing taste for colour, there is an absence of use of the more unusual pigments, such as lazurite, and of the more specialised techniques of wall preparation, such as the use of gypsum. Purple is again in evidence and, as in the first colonial phase, it analyses as caput mortuum, the local and cheaper substitute for the expensive organic purple dye. Although such a palette is parallelled by a number of rural villa

Table 8 Pigment use at Lincoln. Colour Black Green Pink Purple Red White/cream Yellow

Military phase

Early colony *(carbon) Viridian, terre verte

*(haematite) *(calcium carbonate, quartz)

(*) Sample analysed; (+) visual identification, no result on analysis.

*(haematite) *(calcite) *(goethite)

Later colony * *(haematite, calcium carbonate) *(haematite) *(haematite) *(calcite)

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Table 9 Summary of pigment use at Colchester and Lincoln. Colour

Military phase Colchester

Early colony Lincoln

Colchester

Aquamarine Black Blue Green Grey Pink Purple Red Yellow White

+

+ +

+ +

+

Total

4

2

+ + + + +

Later colony Lincoln + +

Colchester + + + + +

+

+ + +

+ + + +

6

5

9

Lincoln

+ + + + + 5

Note: White and cream, which were both present at both sites in all periods are treated as a single entry for the purposes of this table; dark red and red are likewise treated as a single entry.

sites in Northamptonshire, it must be remembered that the Colchester palette is dated to the mid-first century AD, a full century before the Northamptonshire sites. At those villa sites, moreover, it appears that caput mortuum was a specialised recipe, not known to all painters and decorators and, therefore, perhaps, more highly prized for its reflective qualities than simple pigment mixtures which superficially replicated the colour. In contrast to this complex and apparently sophisticated use of pigments at Colchester, the evidence from Lincoln indicates an altogether simpler story [Table 8]. As described above, the first military phase at Lincoln is represented by only two pigments, red and white. Whilst there is a small increase in the number of pigments in use in the early colonial phase, from two to five, this does not include any unusual or exotic techniques for display of these pigments. Indeed, the character of the palette and wall preparation is entirely unremarkable. In contrast, the equivalent phase at Colchester saw the introduction of specialised wall preparation techniques and the application of expensive pigments, such as purple (caput mortuum) and lazurite. The later colony at Lincoln reveals a similar picture, with some variation in colour use, but no overall increase in the breadth of palette. It is significant that the “purple” pigment, encountered for the first time in the later colony phase at Lincoln analyses as unaltered haematite in admixture with carbon, which is now better described as a very deep red colour – it is not the specialised recipe for use of the true purple caput mortuum pigment. A comparison of these two urban centres of Lincoln and Colchester [Table 9] highlights the contrasting experience of these two colonies. Starting from similar legionary military beginnings, there is already a contrast between the richer palette at Colchester and the limited range of colours used at Lincoln. Whilst both settlements see an increase in the variety of colours used in the first colonial phase, it is only at Colchester that unusual, expensive pigments and techniques are employed. In the later colonial period, Lincoln appears to stagnate in terms of the palette range, at a time when Colchester continues to see development and an increase in colour usage. The citizens of Colchester emerge as a population which was capable of attracting a level of investment and expertise in wall painting apparently unavailable to their counterparts at Lincoln. A degree of caution in this interpretation is required, given the small sample sets which have been studied here. Nevertheless, the results of this study do raise some interesting questions for future debate: • Why should Colchester’s experience have been so different from the settlement at Lincoln, given their similar origins and status?

• How far were the local urban elites at centres like St. Albans able to follow the lead of high prestige centres such as Colchester in decorating their town houses? • Can we see the beginnings of the rural villa wall painting repertoire emerging in 1st century Colchester, in particular with the development of the new purple pigment, caput mortuum, and the use of specialised wall preparations to produce enhanced effects? To answer such questions will require further studies of this kind, but we believe that sufficient novel information has emerged from the Raman spectroscopic analyses to demonstrate the potential of the scientific approach to pigment recognition in association with established historical inference. 5. Conclusions Analysis of sample sets from the two Romano-British urban centres of Colchester and Lincoln indicate significant contrasts in the nature of wall painting techniques and palette use. Colchester appears to have developed a more sophisticated painting and decorating craft industry and demonstrates the earliest yet known examples of the use of caput mortuum in Roman Britain. As such, it may be seen as the beginnings of the craft skill, which has been found employed in a range of 2nd century villas in Northamptonshire. Whilst Colchester exhibits evidence for possible overseas links and the assimilation of ground preparation ideas, the character of the craft at Lincoln appears entirely local in origin and shows little evidence for development as took place at Colchester. Acknowledgements PSM would like to acknowledge the support of both the Roman Society and the Society of Antiquaries of London for financial support, which contributed to this research; the authors gratefully acknowledge Michael Jones (City of Lincoln) and Philip Crummy (Colchester Archaeological Trust) for permission to access the samples analysed. References [1] H.G.M. Edwards, L.F.C. de Oliveira, P. Middleton, R.L. Frost, Analyst 127 (2002) 277–281. [2] H.G.M. Edwards, P.S. Middleton, S.E. Jorge Villar, de FariaF D.L.A., Analytica Chimica Acta 484 (2003) 211–221. [3] N.F. Nik Hassan, H.G.M. Edwards, P.S. Middleton, in: P.M. Fredericks, R.L. Frost, L. Rintoul (Eds.), Proceedings of the XIXth International Conference on Raman Spectroscopy (ICORS XIX), Gold Coast, Australia, CSIRO Publishing, Canberra, Australia, 2004, P-179, pp. 596–597.

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[4] P.S. Middleton, H.G.M. Edwards, N.F. Nik Hassan, in: M. Picollo (Ed.), Proceedings of the Sixth Infrared and Raman Users’ Group Conference (IRUG VI), Florence, Italy, March/April 2004, Istituto di Fisica Applicata “Nello Carrara”, Il Prato/IFACCNR Publishing, Florence, Italy, 2005, pp. 198–204. [5] Pliny the Elder, Natural History in Ten Volumes, vol. IX, 3rd ed. (H. Rackham, Trans.), Loeb Classical Library, Cambridge, MA, USA, 1968, Books XXXIII–XXXV. [6] Vitruvius, On Architecture in Two Volumes, vol. II, 5th ed. (F. Granger, Trans.), Loeb Classical Library, Cambridge, MA, USA, 1985. [7] P.S. Middleton, H.G.M. Edwards, S.E. Jorge Villar, Coloured in Colchester: a Raman spectroscopic study of Romano-British painted wall plaster from the roman town of Colchester, in: P. Ottaway (Ed.), A Victory Celebration: Papers on the Archaeology of Colchester and Late-Iron Age – Roman Britain, Colchester Archaeological Trust, Colchester, UK, 2006, pp. 69–74, Chapter 6. [8] M.J. Jones, Roman Lincoln: Conquest, Colony and Capital, Tempus Books, Stroud, 2002.

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