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Use of Spanish broom (Spartium junceum L.) canvas as a painting support: Evaluation of the effects of environmental conditions
Journal of Cultural Heritage 10 (2009) 396–402
Original article
Use of Spanish broom (Spartium junceum L.) canvas as a painting support: Evaluation of the effects of environmental conditions Teresa Cerchiara a,∗ , Giuseppe Chidichimo a , Maria Caterina Gallucci a , Rita Ferraro a , Danilo Vuono b , Alfonso Nastro b b
a Department of Chemistry, Calabria University, Ponte P. Bucci, 87036 Arcavacata di Rende (CS), Italy Department of Territorial Planning, Calabria University, Ponte P. Bucci, 87036 Arcavacata di Rende (CS), Italy
Received 1st February 2008; accepted 10 December 2008
Abstract One of the problems in the field of cultural heritage is the degradation of artworks and especially paintings. They appear very sensitive to environmental conditions. In this work, Spanish broom canvas is proposed as a novel painting support. In order to assess the deterioration properties of this new type of canvas, three degradation processes (exposure to wet atmosphere, to acidic attack and to UV light) were simulated and investigated. The deterioration state of the samples was monitored with Infrared Spectroscopy (FT-IR) and Thermogravimetric Analysis (TGA). The structure of the canvas was also analyzed by Scanning Electron Microscopy (SEM). These techniques were successfully applied to study the occurrence significant changes of samples. The exposure to acidic and UV attack produced deep changes on the samples (only on the canvas surface in the case of UV light), while no significant effect was identified on the sample after the exposure to wet atmosphere. The results obtained from Spanish broom canvas are reported in comparison to flax canvas. © 2009 Elsevier Masson SAS. All rights reserved. Keywords: Canvas painting analysis; Spanish broom; Flax; TGA; FT-IR
1. Introduction The use of textile as a painting support dates back to ancient Egyptian civilization [1]. In Europe, the decoration of churches and religious symbols took precedence until the Renaissance era, when a vast number of paintings originated. The oldest remaining European paintings supported by textile date back to the 15th century (a famous example is a Venetian scene produced on canvas by Gentile Bellini around 1476); before that, wood panels were usually used. From the 16th century, fabrics began to replace wood and became the principal support for oil-based painting. Several types of fibers have been used to construct canvas: animal fibers, such as wool or silk, or vegetable fibers provided by hemp, flax, cotton and jute. The textile obtained from flax fibers offers greater solidity, stability and resistance to time and pollution rather than other organic materials used for this particular purpose; so flax is
∗
Corresponding author. Tel: +39 0984 492 006; fax: +39 0984 492 041. E-mail address: [email protected] (T. Cerchiara).
1296-2074/$ – see front matter © 2009 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.culher.2008.12.002
usually preferred for forming the basic material of painting canvas. Spanish broom fibers (cellulose 91.7%, pentosan 4.1%, lignin 3.2% [2]) have better mechanical properties (Table 1) than those of common bast fibers such as flax (cellulose 71%, hemicellulose 20%, lignin 2.2% [3]). It can be useful as reinforcement of composites, textile and other fibrous application [4]. In particular, attention was focused on the fact that Spanish broom fibers are more elastic (allowing a better and easier manufacturing of Spanish broom fibers in weaving) and stronger than flax fibers, as shown by the higher strain at break and higher tenacity (Table 1). This also means that the Spanish broom canvas keeps its original tension as painting support and no deformation on the paint film is evident. Instead, flax canvas, in the meantime, loses its original tension showing waves that can cause damages such as foldings and cracks on the paint film. For such reason, the idea to use Spanish broom canvas as a painting support was conceived and led our laboratory to manufacture the first oil painting on Spanish broom canvas [3] (Fig. 1). The principal aim of this work is the study of the degradation of Spanish broom canvas during the exposure to environmental
T. Cerchiara et al. / Journal of Cultural Heritage 10 (2009) 396–402 Table 1 Tensile properties of Spanish broom fibers compared with flax.
Spanish broom Flax
Strain at break (%)
Tenacity (cN/tex)
4.7 1.9
20.4 16.9
397
• exposure to acidic attack; • exposure to wet atmosphere. 2.2.1. Exposure to UV light The simulation of exposure to sunlight was obtained by irradiating the canvas strip with light from a UV lamp (power: 0.7 × 10−3 Watt/cm2 ) for 7 h corresponding to average normal daylight of about 3 years. The infrared (IR) spectra were collected every 1 h of exposure for a total of 7 h. 2.2.2. Exposure to acidic attack The exposure to acidic rain was simulated by treating a canvas strip with a 1.0 MH2 SO4 solution. The IR spectra were registered every 1 h of exposure to the acidic solution for a total of 7 h. 2.2.3. Exposure to wet atmosphere The exposure to moisture was simulated by exposing the canvas strip to vapors deriving from a water bath at 60 ◦ C and 50% relative humidity (R.H). IR spectra were registered after 1 h, 24 h and 10 days of exposure to the wet atmosphere. The wet canvas strip was then swaddled with Parafilm and stored for 60 days. During this period, no mould appeared on the sample surface. 2.3. Flax canvas
Fig. 1. Spanish broom oil painting canvas.
conditions (wet atmosphere, acidic attack and UV light) to evaluate whether or not a relevant damage is occurring and to identify ways to prevent it. The benefits to prevent canvas degradation lie not only in avoiding the canvas failure in itself, but mainly in preventing secondary dramatic effects on painting layers [5]. The data obtained are presented in comparison with flax: the most used canvas in painted manufacts.
Flax canvas strips were subjected to the same treatments (exposure to UV light, acidic attack and wet atmosphere) used in the case of the Spanish broom canvas. 2.4. Scanning Electron Microscopy (SEM) Morphological analysis of the canvas strip was carried out using Scanning Electron Microscopy (SEM), which is the most widely used among the surface analytical techniques. The canvas strips were air-dried and coated with gold-palladium in a sputter coater and observed on a LEO 420 (LEO Electron Microscopy Ltd. Cambridge, England) at 15 kV.
2. Materials and methods
2.5. FT-IR spectroscopy
2.1. Materials
Infrared Spectroscopy (FT-IR) spectra were obtained with a Jasco 430 spectrophotometer using KBr disks. Fibers (1 mg) of canvas strips were dispersed in a matrix of KBr (150 mg), followed by compression to form disks. All spectra were registered from 4000 to 400 cm−1 , with a resolution of 4 cm−1 and 32 scans; the background was collected before each spectrum. Each spectrum was repeated three times; these were then averaged and considered as a single measurement. In order to normalize the infrared spectra obtained, we used the 2900 cm−1 band, assigned to CH stretching vibrations. In FT-IR, it is very important to use a spectral band that does not change during the course of treatment if quantitative comparisons are to be performed. The identification of a reference spectral band that remains completely invariable throughout the whole experiment is difficult. The band that was chosen is the one that showed minor changes during treatments.
Spanish broom canvas was supplied by the Department of Chemistry, University of Calabria, Italy. Flax canvas was obtained from A. Mazziotti, Cosenza, Italy. 2.2. Spanish broom canvas To convert Spanish broom fibers into canvas, first the fiber is separated from the branches of the plant and then intercellular matter is removed as reported by Chidichimo et al. in Italian Patent [6]. As to the evaluation of the effect of different environmental conditions which can cause degradation processes [7,8], we simulated three treatments: • exposure to UV light;
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Fig. 2. A. Scanning Electron Microscopy (SEM) micrograph of Spanish broom canvas strip. B. SEM micrograph of Spanish broom fibers composing canvas. C. Fibers after 7 h of acidic exposure. D. Fibers after 7 h of UV exposure.
2.6. Thermogravimetric analysis (TGA) The canvas strips were heated in a Netzsch 429 Thermogravimetric analysis (TGA) apparatus at a rate of 10 ◦ C min−1 from room temperature to 500 ◦ C. TGA was performed in static air. 3. Results and discussion 3.1. Spanish broom canvas 3.1.1. SEM Fig. 2A shows a low magnified photograph of Spanish broom canvas, while Fig. 2B shows the canvas fiber components.
The longitudinal view of fibers shows that they are well separated and that they are cylindrical in shape with a smooth surface. Spanish broom canvas are tabby weave, which creates a regular painting surface; threads of equal diameter are woven so that they cross one another alternately at right angles. This method of weaving produces the tightest canvas because threads are closely intertwined. The effect of two ageing treatments are shown in Figs. 2C and 2D. Fibers after 7 h exposure to acidic solution show several transversal breaks, indicating an effective degradation process induced on cellulose by acid environments Fig. 2C. Also the fibers exposed for 7 h to UV light irradiation appear quite
Fig. 3. Infrared (IR) spectra of Spanish broom canvas (a) with the correspondent band assignments; Spanish broom canvas after 1 h exposed to acidic attack (b); Spanish broom canvas after 2 h exposed to acidic attack (c); Spanish broom canvas after 7 h exposed to acidic attack (d).
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Fig. 4. Infrared (IR) spectra of Spanish broom canvas (a); Spanish broom canvas after 1 h exposed to UV light (b); after 2 h exposed to UV light (c); after 7 h exposed to UV light (d). The peaks which showed relevant changes during UV exposure are indicated.
damaged, since surface erosion, as well as numerous defects, such as filaments and crazes, are easily evidenced in Fig. 2D. No relevant variations have been evidenced for shorter exposure times (1 h and 2 h) to UV and acidic solutions. Similarly, no effects have been observed after treatment with wet atmosphere (data not reported). 3.1.2. FT-IR IR spectra of samples before and after the acidic attack exposure are shown in Fig. 3. The spectral profiles of the samples exposed to acid for 1 and 2 h are rather similar, indicating similar structures for the cellulose. Nevertheless, all bands of samples assigned to cellulose, such as 1442 cm−1 , 1365 cm−1 and 1045 cm−1 , decrease significantly as a result of the acid degradation. It must be instead noted that the spectrum of sample exposed to acid for 7 h provides evidence a deeper degradation by showing the presence of two bands at 1151 cm−1 and 1056 cm−1 , corresponding respectively to C–O bridge stretching and C–O–C pyranose ring skeletal vibration [9,10]. IR spectra of samples before and after the UV exposure are shown in Fig. 4. It can be noticed that a general decrease of the absorbance intensities of the peaks occurred. Spectral modification are evident after 7 h exposure to UV light (see peaks at 1093 cm−1 , 1047 cm−1 and 981 cm−1 ). Structural modifications at the molecular level thus occur and this must be probably attributed to photoinduced chain scissions [11,12]. The exposure to wet atmosphere did not evidence any relevant change of the absorbance intensities of the peaks (Fig. 5). No mould appeared on the surface of the canvas strip after 60 days and this can be probably due to the antifungicidal activity of minor percentages of lignin. The stability of Spanish broom canvas in wet atmospheres points out such a canvas as a very good painting support.
3.1.3. TGA A comparison between typical TGA curves obtained for Spanish broom canvas exposed to UV light, acidic attack and wet atmosphere is shown in Fig. 6. After initial loss of moisture at 100–120 ◦ C, weight loss in cellulose occurred. The detailed mechanism of cellulose degradation is not clear, but it is generally accepted that a main reaction at temperatures between 300 ◦ C and 500 ◦ C is chain scission at the 1, 4-glycosidic bonds [13,14]. The initiation (∼300 ◦ C) and culmination (∼475 ◦ C) of the major stage of the degradation were similar for all samples, with the exception of the sample exposed to acidic attack for 7 h exhibiting an initiation temperature of about 340 ◦ C. Such a reduced initiation temperature is probably an indicator of the degradation of cellulose chains. Differential Scanning Calorimetry (DSC) curves of sample exposed to different treatments are reported in Fig. 7. A small endothermic peak, at approximately 75 ◦ C, occurred for all
Fig. 5. Infrared (IR) spectra of Spanish broom canvas (a); Spanish broom canvas after 10 days exposed to wet atmosphere (b).
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Fig. 6. Thermogravimetric analysis (TGA) curves of Spanish broom canvas exposed to three different treatments. Fig. 7. DSC of Spanish broom canvas exposed to three different treatments.
samples due to the water loss. Two exothermic peaks, at approximately 352 ◦ C and 466 ◦ C occurred in all samples, except for the sample exposed to acidic attack for 7 h which shows only one peak at 343 ◦ C. This may be due to a break of glycosidic bonds and inter- and intramolecular hydrogen bonds which are responsible for maintenance of cellulose chains in the form of fibers. Consequently, the thermal stability of sample exposed to acidic attack for 7 h is lower than that of other samples exposed to different treatment. 3.2. Flax canvas 3.2.1. SEM Fig. 8 shows a photograph of flax canvas strip (A) and the SEM micrograph of its component fibers (B). These fibers are
grouped in several bundles; they are cylindrical in shape with a smooth surface and covered with some incrustations. As Spanish broom canvas, flax canvas is tabby weave characterized by regular painting surface. SEM micrographs detailing the morphology of samples treated with different treatment, are shown in Figs. 8C and D. Treating flax fiber with an acid solution for 7 h caused fiber surface cleaning and, at the same time, the occurrence of many cracks (Fig. 8C). Surface erosion showing numerous defects such as filaments and crazes were caused by the UV treatment (7 h exposure). In addition, surface roughness increases (Fig. 8D). Even in this case, fibers do not show a different morphology after the exposure to wet atmospheres (data not reported).
Fig. 8. A. Scanning Electron Microscopy (SEM) micrograph of linen canvas strip. B. SEM micrograph of flax fibers composing canvas. C. Fibers after 7 h of acidic exposure. D. Fibers after 7 h of UV exposure.
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Fig. 9. Infrared (IR) spectra of flax canvas with the correspondent band assignments (a); flax canvas after 1 h exposed to acidic attack (b); flax canvas after 2 h exposed to acidic attack (c); flax canvas after 7 h exposed to acidic attack (d). The peaks which showed relevant changes during this treatment are indicated.
3.2.2. FT-IR Even in this case, results obtained for flax canvas exposed respectively to UV light, acidic attack and wet atmosphere are similar to those above described for Spanish broom canvas. The acidic treatment produces a relevant effect on canvas strip causing degradation of cellulose chains as confirmed by FT-IR spectra reported in Fig. 9. The intensities of peaks decreased with increasing the time of exposure to acid and two new peaks (1031 cm−1 and 983 cm−1 ) appeared indicating that part of cellulose was degraded. For what concerns exposure to UV light, changes are evident after 7 h treatment, indicating photoinduced chain cellulose scissions. In addition, no effect resulted from the exposure of the canvas strip to wet atmosphere (data not reported).
3.2.3. TGA The thermal behavior of flax canvas has been investigated for samples exposed to three different treatments as well. As in the case of Spanish broom canvas, the sample exposed to acidic attack for 7 h exhibits lower initiation temperature (about 340 ◦ C) than other samples exposed to different treatment (Fig. 10). DSC curves of sample exposed to different treatments are reported in Fig. 11. Two exothermic peaks occurred at approximately 354 ◦ C and 484 ◦ C in all samples except sample exposed to acidic attack for 7 h. It only displayed one peak at 344 ◦ C. The difference of degradation temperatures of flax sample exposed to acidic attack, is likely due to a different thermochemical behavior of the cellulose degradation.
Fig. 10. Thermogravimetric analysis (TGA) curves of flax canvas exposed to three different treatments.
Fig. 11. DSC of flax canvas exposed to three different treatments.
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4. Conclusion A new application for Spanish broom canvas as a painting support is proposed. The aim of this paper was to compare the effects produced by the exposure to wet atmosphere, to acidic attack and to UV light on both Spanish broom and flax canvases strips. The conclusion is that the two investigated canvases show an analogous behavior with respect to severe environmental conditions. In particular, it has been shown that the most important degradation factor is linked to the presence of acid conditions. From stability, the point of view and ageing properties of Spanish broom is similar to flax canvas. In addition, we show that the Spanish broom canvas keeps its original tension as painting support and no deformation on the paint film is evident. Instead, flax canvas, during the time, loses its original tension, showing waves that can cause damages such as foldings and cracks on the paint film. So we conclude that Spanish broom canvas can successfully replace the flax canvas. References [1] F. Drago, N. Chiba, Painting canvas synthesis, The Visual Computer 20 (2004) 314–328. [2] UNICAL-CRF Project MIUR no. 987: Sviluppo ed ottimizzazione di processi per l’ottenimento di materie prime e semilavorati derivati da fibre di ginestra, Italy, 2003–2006. [3] R. Ferraro, Sperimentazione di tele di Spartium junceum L. come supporti per dipinti, Thesis, Calabria University, Italy, 2007.
[4] T. Cerchiara, G. Chidichimo, M.C. Gallucci, M. Vetere, Morphology and properties of natural cellulose fibers from Spanish broom (Spartium junceum L.), In: Proceedings of NanoItalTex 2007, November 21–22, NanoItalTex, Milan, Italy, 2007, p. 46. [5] G. Foster, M. Odlyha, S. Hackney, Evaluation of the effects of environmental conditions and preventive conservation treatment on painting canvases, Thermochimica Acta 294 (1997) 81–89. [6] G. Chidichimo, B. Gabriele, G. Salerno, C. Alampi, T. Cerchiara, M. Vetere. Processo chimicofisico per la produzione di fibre vegetali. Calabria University, Italian Patent (2006) CZ2006A00006. [7] E. Marengo, E. Robotti, M.C. Liparota, M.C. Gennaro, A method for monitoring the surface conservation of wooden objects by Raman spectroscopy and multivariate control charts, Analytical Chemistry 75 (2003) 5567–5574. [8] E. Marengo, E. Robotti, M.C. Liparota, M.C. Gennaro, Monitoring of pigmented and wooden surfaces in accelerated ageing processes by FT-Raman spectroscopy and multivariate control charts, Talanta 63 (2004) 987–1002. [9] N. Katsuda, T. Omura, T. Tagagishi, Dyes and Pigments 3 (1997) 231–241. [10] M.F. Mecklenburg, C.S. Tumosa, Temperature and relative humidity effects on the mechanical and chemical stability of collections, Ashrae Journal 41 (1999) 77–82. [11] E. Marengo, M.C. Liparota, E. Robotti, M. Bobba, Monitoring of paintings under exposure to UV light by ATR-FT-IR spectroscopy and multivariate control charts, Vibrational Spectroscopy 40 (2006) 225–234. [12] V.R. Botaro, C.G. Dos Santos, G. Arantes Junior, A.R. Da Costa, Chemical modification of lignocellulosic materials by irradiation with Nd - YAG pulsed laser, Applied Surface Science 183 (2001) 120–125. [13] M.Z. Sefain, M.H. Fadl, N.A. El Wakil, M.S.A. El-Salam, Polymer Degradation and Stability 50 (1995) 195. [14] D.J. Carr, M. Odlyha, N. Cohen, A. Phenix, R.D. Hibberd, Thermal analysis of new, artificially aged and archival linen, Journal of Thermal analysis and Calorimetry 73 (2003) 97–104.
Original article
Use of Spanish broom (Spartium junceum L.) canvas as a painting support: Evaluation of the effects of environmental conditions Teresa Cerchiara a,∗ , Giuseppe Chidichimo a , Maria Caterina Gallucci a , Rita Ferraro a , Danilo Vuono b , Alfonso Nastro b b
a Department of Chemistry, Calabria University, Ponte P. Bucci, 87036 Arcavacata di Rende (CS), Italy Department of Territorial Planning, Calabria University, Ponte P. Bucci, 87036 Arcavacata di Rende (CS), Italy
Received 1st February 2008; accepted 10 December 2008
Abstract One of the problems in the field of cultural heritage is the degradation of artworks and especially paintings. They appear very sensitive to environmental conditions. In this work, Spanish broom canvas is proposed as a novel painting support. In order to assess the deterioration properties of this new type of canvas, three degradation processes (exposure to wet atmosphere, to acidic attack and to UV light) were simulated and investigated. The deterioration state of the samples was monitored with Infrared Spectroscopy (FT-IR) and Thermogravimetric Analysis (TGA). The structure of the canvas was also analyzed by Scanning Electron Microscopy (SEM). These techniques were successfully applied to study the occurrence significant changes of samples. The exposure to acidic and UV attack produced deep changes on the samples (only on the canvas surface in the case of UV light), while no significant effect was identified on the sample after the exposure to wet atmosphere. The results obtained from Spanish broom canvas are reported in comparison to flax canvas. © 2009 Elsevier Masson SAS. All rights reserved. Keywords: Canvas painting analysis; Spanish broom; Flax; TGA; FT-IR
1. Introduction The use of textile as a painting support dates back to ancient Egyptian civilization [1]. In Europe, the decoration of churches and religious symbols took precedence until the Renaissance era, when a vast number of paintings originated. The oldest remaining European paintings supported by textile date back to the 15th century (a famous example is a Venetian scene produced on canvas by Gentile Bellini around 1476); before that, wood panels were usually used. From the 16th century, fabrics began to replace wood and became the principal support for oil-based painting. Several types of fibers have been used to construct canvas: animal fibers, such as wool or silk, or vegetable fibers provided by hemp, flax, cotton and jute. The textile obtained from flax fibers offers greater solidity, stability and resistance to time and pollution rather than other organic materials used for this particular purpose; so flax is
∗
Corresponding author. Tel: +39 0984 492 006; fax: +39 0984 492 041. E-mail address: [email protected] (T. Cerchiara).
1296-2074/$ – see front matter © 2009 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.culher.2008.12.002
usually preferred for forming the basic material of painting canvas. Spanish broom fibers (cellulose 91.7%, pentosan 4.1%, lignin 3.2% [2]) have better mechanical properties (Table 1) than those of common bast fibers such as flax (cellulose 71%, hemicellulose 20%, lignin 2.2% [3]). It can be useful as reinforcement of composites, textile and other fibrous application [4]. In particular, attention was focused on the fact that Spanish broom fibers are more elastic (allowing a better and easier manufacturing of Spanish broom fibers in weaving) and stronger than flax fibers, as shown by the higher strain at break and higher tenacity (Table 1). This also means that the Spanish broom canvas keeps its original tension as painting support and no deformation on the paint film is evident. Instead, flax canvas, in the meantime, loses its original tension showing waves that can cause damages such as foldings and cracks on the paint film. For such reason, the idea to use Spanish broom canvas as a painting support was conceived and led our laboratory to manufacture the first oil painting on Spanish broom canvas [3] (Fig. 1). The principal aim of this work is the study of the degradation of Spanish broom canvas during the exposure to environmental
T. Cerchiara et al. / Journal of Cultural Heritage 10 (2009) 396–402 Table 1 Tensile properties of Spanish broom fibers compared with flax.
Spanish broom Flax
Strain at break (%)
Tenacity (cN/tex)
4.7 1.9
20.4 16.9
397
• exposure to acidic attack; • exposure to wet atmosphere. 2.2.1. Exposure to UV light The simulation of exposure to sunlight was obtained by irradiating the canvas strip with light from a UV lamp (power: 0.7 × 10−3 Watt/cm2 ) for 7 h corresponding to average normal daylight of about 3 years. The infrared (IR) spectra were collected every 1 h of exposure for a total of 7 h. 2.2.2. Exposure to acidic attack The exposure to acidic rain was simulated by treating a canvas strip with a 1.0 MH2 SO4 solution. The IR spectra were registered every 1 h of exposure to the acidic solution for a total of 7 h. 2.2.3. Exposure to wet atmosphere The exposure to moisture was simulated by exposing the canvas strip to vapors deriving from a water bath at 60 ◦ C and 50% relative humidity (R.H). IR spectra were registered after 1 h, 24 h and 10 days of exposure to the wet atmosphere. The wet canvas strip was then swaddled with Parafilm and stored for 60 days. During this period, no mould appeared on the sample surface. 2.3. Flax canvas
Fig. 1. Spanish broom oil painting canvas.
conditions (wet atmosphere, acidic attack and UV light) to evaluate whether or not a relevant damage is occurring and to identify ways to prevent it. The benefits to prevent canvas degradation lie not only in avoiding the canvas failure in itself, but mainly in preventing secondary dramatic effects on painting layers [5]. The data obtained are presented in comparison with flax: the most used canvas in painted manufacts.
Flax canvas strips were subjected to the same treatments (exposure to UV light, acidic attack and wet atmosphere) used in the case of the Spanish broom canvas. 2.4. Scanning Electron Microscopy (SEM) Morphological analysis of the canvas strip was carried out using Scanning Electron Microscopy (SEM), which is the most widely used among the surface analytical techniques. The canvas strips were air-dried and coated with gold-palladium in a sputter coater and observed on a LEO 420 (LEO Electron Microscopy Ltd. Cambridge, England) at 15 kV.
2. Materials and methods
2.5. FT-IR spectroscopy
2.1. Materials
Infrared Spectroscopy (FT-IR) spectra were obtained with a Jasco 430 spectrophotometer using KBr disks. Fibers (1 mg) of canvas strips were dispersed in a matrix of KBr (150 mg), followed by compression to form disks. All spectra were registered from 4000 to 400 cm−1 , with a resolution of 4 cm−1 and 32 scans; the background was collected before each spectrum. Each spectrum was repeated three times; these were then averaged and considered as a single measurement. In order to normalize the infrared spectra obtained, we used the 2900 cm−1 band, assigned to CH stretching vibrations. In FT-IR, it is very important to use a spectral band that does not change during the course of treatment if quantitative comparisons are to be performed. The identification of a reference spectral band that remains completely invariable throughout the whole experiment is difficult. The band that was chosen is the one that showed minor changes during treatments.
Spanish broom canvas was supplied by the Department of Chemistry, University of Calabria, Italy. Flax canvas was obtained from A. Mazziotti, Cosenza, Italy. 2.2. Spanish broom canvas To convert Spanish broom fibers into canvas, first the fiber is separated from the branches of the plant and then intercellular matter is removed as reported by Chidichimo et al. in Italian Patent [6]. As to the evaluation of the effect of different environmental conditions which can cause degradation processes [7,8], we simulated three treatments: • exposure to UV light;
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Fig. 2. A. Scanning Electron Microscopy (SEM) micrograph of Spanish broom canvas strip. B. SEM micrograph of Spanish broom fibers composing canvas. C. Fibers after 7 h of acidic exposure. D. Fibers after 7 h of UV exposure.
2.6. Thermogravimetric analysis (TGA) The canvas strips were heated in a Netzsch 429 Thermogravimetric analysis (TGA) apparatus at a rate of 10 ◦ C min−1 from room temperature to 500 ◦ C. TGA was performed in static air. 3. Results and discussion 3.1. Spanish broom canvas 3.1.1. SEM Fig. 2A shows a low magnified photograph of Spanish broom canvas, while Fig. 2B shows the canvas fiber components.
The longitudinal view of fibers shows that they are well separated and that they are cylindrical in shape with a smooth surface. Spanish broom canvas are tabby weave, which creates a regular painting surface; threads of equal diameter are woven so that they cross one another alternately at right angles. This method of weaving produces the tightest canvas because threads are closely intertwined. The effect of two ageing treatments are shown in Figs. 2C and 2D. Fibers after 7 h exposure to acidic solution show several transversal breaks, indicating an effective degradation process induced on cellulose by acid environments Fig. 2C. Also the fibers exposed for 7 h to UV light irradiation appear quite
Fig. 3. Infrared (IR) spectra of Spanish broom canvas (a) with the correspondent band assignments; Spanish broom canvas after 1 h exposed to acidic attack (b); Spanish broom canvas after 2 h exposed to acidic attack (c); Spanish broom canvas after 7 h exposed to acidic attack (d).
T. Cerchiara et al. / Journal of Cultural Heritage 10 (2009) 396–402
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Fig. 4. Infrared (IR) spectra of Spanish broom canvas (a); Spanish broom canvas after 1 h exposed to UV light (b); after 2 h exposed to UV light (c); after 7 h exposed to UV light (d). The peaks which showed relevant changes during UV exposure are indicated.
damaged, since surface erosion, as well as numerous defects, such as filaments and crazes, are easily evidenced in Fig. 2D. No relevant variations have been evidenced for shorter exposure times (1 h and 2 h) to UV and acidic solutions. Similarly, no effects have been observed after treatment with wet atmosphere (data not reported). 3.1.2. FT-IR IR spectra of samples before and after the acidic attack exposure are shown in Fig. 3. The spectral profiles of the samples exposed to acid for 1 and 2 h are rather similar, indicating similar structures for the cellulose. Nevertheless, all bands of samples assigned to cellulose, such as 1442 cm−1 , 1365 cm−1 and 1045 cm−1 , decrease significantly as a result of the acid degradation. It must be instead noted that the spectrum of sample exposed to acid for 7 h provides evidence a deeper degradation by showing the presence of two bands at 1151 cm−1 and 1056 cm−1 , corresponding respectively to C–O bridge stretching and C–O–C pyranose ring skeletal vibration [9,10]. IR spectra of samples before and after the UV exposure are shown in Fig. 4. It can be noticed that a general decrease of the absorbance intensities of the peaks occurred. Spectral modification are evident after 7 h exposure to UV light (see peaks at 1093 cm−1 , 1047 cm−1 and 981 cm−1 ). Structural modifications at the molecular level thus occur and this must be probably attributed to photoinduced chain scissions [11,12]. The exposure to wet atmosphere did not evidence any relevant change of the absorbance intensities of the peaks (Fig. 5). No mould appeared on the surface of the canvas strip after 60 days and this can be probably due to the antifungicidal activity of minor percentages of lignin. The stability of Spanish broom canvas in wet atmospheres points out such a canvas as a very good painting support.
3.1.3. TGA A comparison between typical TGA curves obtained for Spanish broom canvas exposed to UV light, acidic attack and wet atmosphere is shown in Fig. 6. After initial loss of moisture at 100–120 ◦ C, weight loss in cellulose occurred. The detailed mechanism of cellulose degradation is not clear, but it is generally accepted that a main reaction at temperatures between 300 ◦ C and 500 ◦ C is chain scission at the 1, 4-glycosidic bonds [13,14]. The initiation (∼300 ◦ C) and culmination (∼475 ◦ C) of the major stage of the degradation were similar for all samples, with the exception of the sample exposed to acidic attack for 7 h exhibiting an initiation temperature of about 340 ◦ C. Such a reduced initiation temperature is probably an indicator of the degradation of cellulose chains. Differential Scanning Calorimetry (DSC) curves of sample exposed to different treatments are reported in Fig. 7. A small endothermic peak, at approximately 75 ◦ C, occurred for all
Fig. 5. Infrared (IR) spectra of Spanish broom canvas (a); Spanish broom canvas after 10 days exposed to wet atmosphere (b).
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Fig. 6. Thermogravimetric analysis (TGA) curves of Spanish broom canvas exposed to three different treatments. Fig. 7. DSC of Spanish broom canvas exposed to three different treatments.
samples due to the water loss. Two exothermic peaks, at approximately 352 ◦ C and 466 ◦ C occurred in all samples, except for the sample exposed to acidic attack for 7 h which shows only one peak at 343 ◦ C. This may be due to a break of glycosidic bonds and inter- and intramolecular hydrogen bonds which are responsible for maintenance of cellulose chains in the form of fibers. Consequently, the thermal stability of sample exposed to acidic attack for 7 h is lower than that of other samples exposed to different treatment. 3.2. Flax canvas 3.2.1. SEM Fig. 8 shows a photograph of flax canvas strip (A) and the SEM micrograph of its component fibers (B). These fibers are
grouped in several bundles; they are cylindrical in shape with a smooth surface and covered with some incrustations. As Spanish broom canvas, flax canvas is tabby weave characterized by regular painting surface. SEM micrographs detailing the morphology of samples treated with different treatment, are shown in Figs. 8C and D. Treating flax fiber with an acid solution for 7 h caused fiber surface cleaning and, at the same time, the occurrence of many cracks (Fig. 8C). Surface erosion showing numerous defects such as filaments and crazes were caused by the UV treatment (7 h exposure). In addition, surface roughness increases (Fig. 8D). Even in this case, fibers do not show a different morphology after the exposure to wet atmospheres (data not reported).
Fig. 8. A. Scanning Electron Microscopy (SEM) micrograph of linen canvas strip. B. SEM micrograph of flax fibers composing canvas. C. Fibers after 7 h of acidic exposure. D. Fibers after 7 h of UV exposure.
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Fig. 9. Infrared (IR) spectra of flax canvas with the correspondent band assignments (a); flax canvas after 1 h exposed to acidic attack (b); flax canvas after 2 h exposed to acidic attack (c); flax canvas after 7 h exposed to acidic attack (d). The peaks which showed relevant changes during this treatment are indicated.
3.2.2. FT-IR Even in this case, results obtained for flax canvas exposed respectively to UV light, acidic attack and wet atmosphere are similar to those above described for Spanish broom canvas. The acidic treatment produces a relevant effect on canvas strip causing degradation of cellulose chains as confirmed by FT-IR spectra reported in Fig. 9. The intensities of peaks decreased with increasing the time of exposure to acid and two new peaks (1031 cm−1 and 983 cm−1 ) appeared indicating that part of cellulose was degraded. For what concerns exposure to UV light, changes are evident after 7 h treatment, indicating photoinduced chain cellulose scissions. In addition, no effect resulted from the exposure of the canvas strip to wet atmosphere (data not reported).
3.2.3. TGA The thermal behavior of flax canvas has been investigated for samples exposed to three different treatments as well. As in the case of Spanish broom canvas, the sample exposed to acidic attack for 7 h exhibits lower initiation temperature (about 340 ◦ C) than other samples exposed to different treatment (Fig. 10). DSC curves of sample exposed to different treatments are reported in Fig. 11. Two exothermic peaks occurred at approximately 354 ◦ C and 484 ◦ C in all samples except sample exposed to acidic attack for 7 h. It only displayed one peak at 344 ◦ C. The difference of degradation temperatures of flax sample exposed to acidic attack, is likely due to a different thermochemical behavior of the cellulose degradation.
Fig. 10. Thermogravimetric analysis (TGA) curves of flax canvas exposed to three different treatments.
Fig. 11. DSC of flax canvas exposed to three different treatments.
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4. Conclusion A new application for Spanish broom canvas as a painting support is proposed. The aim of this paper was to compare the effects produced by the exposure to wet atmosphere, to acidic attack and to UV light on both Spanish broom and flax canvases strips. The conclusion is that the two investigated canvases show an analogous behavior with respect to severe environmental conditions. In particular, it has been shown that the most important degradation factor is linked to the presence of acid conditions. From stability, the point of view and ageing properties of Spanish broom is similar to flax canvas. In addition, we show that the Spanish broom canvas keeps its original tension as painting support and no deformation on the paint film is evident. Instead, flax canvas, during the time, loses its original tension, showing waves that can cause damages such as foldings and cracks on the paint film. So we conclude that Spanish broom canvas can successfully replace the flax canvas. References [1] F. Drago, N. Chiba, Painting canvas synthesis, The Visual Computer 20 (2004) 314–328. [2] UNICAL-CRF Project MIUR no. 987: Sviluppo ed ottimizzazione di processi per l’ottenimento di materie prime e semilavorati derivati da fibre di ginestra, Italy, 2003–2006. [3] R. Ferraro, Sperimentazione di tele di Spartium junceum L. come supporti per dipinti, Thesis, Calabria University, Italy, 2007.
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