IDENTIFICATION OF DYES ON OLD TEXTILES
ONLY A FEW EXPERTS are capable of identifying dyes on old textiles, because most of the methods currently used require expensive apparatus, are time-consuming, and can be evaluated only by people with much experience, or because the necessary collection of authentic samples is not available. I wish to introduce here a method of analysis that is simple, quick, and cheap and is suitable for identifying the most important natural dyes on textiles. However, even this method cannot be carried out without making color comparisons, and I have therefore included a list of suppliers of natural dyes and books on dyeing with natural dyes (Appendices 1 and 2).
In contrast to methods previously known, I identify the natural dyes on the fibres, without taking them up into solution. Many of the natural dyes are mordant dyes, present on the fibre as insoluble lakes, for example aluminum lakes. In such cases one can form different lakes by boiling with aqueous solutions of tin, aluminum, iron, copper, or uranium salts, and then one obtains a series of lakes of different shades. By making comparisons with known dyeings it is very often possible to make an unambiguous identification of particular natural mordant dyes. This method of analysis is really based on the method of dyeing whereby the color is first developed on the fibre. This method of dyeing with mordant dyes is used when a metal salt is not suitable for direct mordanting of the fibre. For instance, one can dye wool mordanted with alum and then treat it with an aqueous solution of, say, copper sulfate, forming the copper lake on the fibre.
I shall give a short sketch of the method of analysis and then enlarge on this with the aid of specific examples. However, I should first like to mention some preliminary tests, which in some cases can give important indications.