| Chemical analysis of natural dyes in textiles and other objects of historical interest can provide valuable information on where, when and how these materials were made. In order to obtain the dyes in their native state, new, mild extraction methods, which use formic acid or ethylenediaminetetraacetic acid instead of the traditional concentrated hydrochloric acid, were developed. The extracts were then analyzed using high performance liquid chromatography (HPLC) with diode array and mass spectrometric detection, the latter detection method being new to dye analysis. These techniques were applied primarily to yellow-dyed textiles and to plant dyestuffs that contain yellow dyes, most of which are glycosides that are hydrolyzed by the strong acid (HCl) used in earlier studies. Each dyestuff generates a unique profile or "fingerprint" that can, in many cases, serve to identify the source of the dye in a dyed object. Natural dyes (mostly yellow) from more than 200 plants or insects were analyzed. The light stability and acid resistance of the most common category of yellow dyes, namely flavonoid compounds, were also studied. The new extraction and analysis methods have been successfully applied to historical textile samples, ranging in age from 150 to 3000 years, from Peru, China and Uzbekistan. We not only identified some of the biological sources of dye components, but also discovered that processing of the dyestuff, e.g., by rapid heating to inactivate deglycosylating enzymes, can play an important role in determining which dye components are retained on the textiles. The same process also results in dyes that are more light-stable. The data from this study, comprised of HPLC retention times, UV/Visible and mass spectra, will be deposited in an online, freely-accessible database which can be used by scientists and conservators worldwide. The results in this thesis provide new insights into historically important natural dyes and can be employed in research on, and conservation of, historical textiles. |
