Fibres Were Viewed Under a Light Microscope at ×80 Magnification To
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Scottish Archaeological Internet Reports 81 2019 5. THE DYE ANALYSIS: PART 1 5.3 Experimental Anita Quye 5.3.1 Sample descriptions The dye analysis was done as two separate reports, Fibres were viewed under a light microscope at which is how the text is laid out. The tables have ×80 magnification to describe the colours given in been combined for easier reference. Table 5. 5.1 Summary 5.3.2 High-performance liquid chromatography with photodiode array detection Eleven fragments of striped woollen textiles recovered from Siller Holes were analysed by Samples were prepared and analysed as described high-performance liquid chromatography with in Appendix 1. Full results can be consulted; they photodiode array detection to identify any will be held with the original data, currently at the dye which may still have been present. Nine National Museums of Scotland Collections Centre samples were found to contain traces of one, or prior to their being deposited in Canmore. a combination, of the indigoid, flavonoid and 5.4 Results anthraquinoid compounds associated with natural dyestuffs. In some cases, these could be more Component retention times and spectra were specifically identified as indigotin (blue), luteolin compared with those for reference dyes. Table (yellow) and carminic acid (red). 6 summarises the data. Although several peaks While it is not possible to identify the exact appeared in the reagent blank chromatogram arising sources of the dyestuffs because of the widespread from sample preparation, these did not interfere occurrence of these natural dye components, the with the dye components. study has nevertheless shown that the analysed textiles had been dyed. Further analysis of the 5.5 Discussion two fragments found to contain carminic acid A number of chemicals associated with natural dyes may reveal minor components which could show were detected and identified in the textile fragments which variety of cochineal (European or Mexican) from Siller Holes. More detailed assessments of the had been used. This information might assist with results follow. dating the finds. 5.5.1 Anthraquinones 5.2 Introduction Anthraquinones are present in many plants and Fieldwalking at the lead mining site at Siller insects which produce red dyes. A compound in Holes, near West Linton in Peeblesshire, recovered both Samples 5 and 9 gave a good chromatographic a number of leather and fabric fragments. Some and spectral match with carminic acid, a major of the textiles were coloured (red, green, brown anthraquinone component of several historically and black), striped and made from coarse wool. important insect red dyes. As a trace level It has been proposed that these striped woollen compound in Sample 10 showed spectral, but fragments date from the late medieval period, not chromatographic, similarity to carminic acid, perhaps imported into Scotland. The textiles it can only be concluded that an unspecified may also have been made from recycled quality anthraquinone compound is present. garments. Until the importation of Mexican cochineal Samples were submitted for dye analysis (Dactylopius coccus), both Polish cochineal by photodiode array high-performance liquid (Porphyrophora polonica) and Armenian cochineal chromatography to determine whether the textiles (Porphyrophora hameli), along with kermes (Kermes had been dyed and if this revealed more about their kerria), were the main sources of insect red dyes provenance. in western Europe (Wouters & Verhecken 1989). SAIR 81 | 48 Scottish Archaeological Internet Reports 81 2019 Although more expensive, Mexican cochineal 5.5.2 Flavonoids, including luteolin quickly established itself as a much better alternative to kermes and the European cochineals because Analysis revealed that Sample 4 contained the of its superior dye content. This is reflected in flavonoid luteolin, one of the most widespread historical accounts and testified to by dye analysis flavonoids found in yellow-producing dye plants. results for red-coloured quality 14th- to 17th- The two most popular western European yellow dyestuffs were weld (Reseda Iuteola L.) and dyer’s century European textiles, which show a distinct greenweed (Genista tinctoria L.). Weld maintained transition in the preferred insect red from European its reputation as one of the best fast yellow colours to American cochineal over this period (Hofenk de for many centuries in western Europe until the Graaff 1983; Wouters & Verhecken 1989; Cardon advent of more light-fast and cheaper yellows, like 1990: 345–78). quercitron bark, in the late 18th century. An analytical study of the anthraquinone content Unfortunately, secondary flavonoids, such of historical insect red dyes has shown that different as apigenin and genistein, which could have sources for these dyes may be identified from the enabled the plant source to be determined, were relative ratios and presence of certain anthraquinone not detectable in Sample 4 from Siller Holes. An compounds (Wouters & Verhecken 1989). If the unidentified compound with a flavonoid-like carminic acid detected in the Siller Holes samples UV-visible spectrum was detected in Sample 8. was found to derive from Mexican cochineal, Yellow and blue dyes were often combined to then the textiles, if European in origin, are almost produce a reasonably fast green colour. Although certain to date from the late 14th century at the Samples 1, 2 and 3 appeared green, no additional earliest. However, a European insect source for this dye compounds besides indigotin could be detected. red dye could indicate that the textiles are older. This may be for two reasons: (i) burial has given the Unfortunately, none of the characteristic secondary fibres a yellow tinge through wool discolouration dye components could be detected in either Sample or absorption of tannins so that they appear green; 5 or Sample 9 of the Siller Holes textiles, and so it or (ii) the yellow dye(s) have degraded and are no is not possible to classify the source(s). longer identifiable. The anthraquinoid compound detected in Sample 5.6 Conclusions 11 was chromatographically more similar to those present in plant, rather than insect, dyes, although This preliminary study of textile fragments from it could not be identified conclusively. Siller Holes has revealed that 9 of the 11 samples analysed contain traces of major chemicals relating 5.5.2 Indigotin to natural yellow, red and/or blue dyes. The dyestuff sources can only be speculated upon Indigotin was identified in Samples 1, 2, 3, 5, 8 because additional characteristic compounds could and 10. This compound is the main colouring not be detected, but the most likely plants and compound of woad (Isatis tinctoria), a plant insects to have been used were popular for many indigenous to Europe, as well as Indian indigo centuries. (Indigofera tinctoria L.) and synthetic indigo. It is Further analysis of larger quantities of red fibres not analytically possible to distinguish between the from SH 118 (3) and SH 139 might reveal more two natural sources, or even between synthetic and chemical information which could help characterise natural sources, at present. the insect dye source. SAIR 81 | 49.