1 INTRODUCTION

Not long ago, historic dyestuff analysis was accomplished by comparing the visible hues of an unknown dyeing against known dyeings and basing conclusions on the best color match. Because of color changes due to fading or aging and variations in the natural sources of the dyes, the constitution of the dyebath, and the fiber substrates, this method is not reliable. Hence researchers have sought more discriminating methods related to the chemical composition of the dyes. These include a systematic series of extractions and chemical reactions (Schweppe 1988), ultraviolet/visible light spectrophotometry (UV/VIS) (Young 1957; Saltzman et al. 1963; Saltzman 1978, 1986, 1992), infrared (IR) spectrometry (Abrahams and Edelstein 1964; Hofenk-de Graaff 1969; Martoglio et al. 1990), thin layer chromatography (TLC) (Geiss-Mooney and Needles 1981; Kharbade and Agrawal 1985; Schweppe 1986, 1988), and high-performance liquid chromatography (HPLC) (Wouters 1985; Wouters and Verhecken 1985, 1989a, 1989b; Walker and Needles 1986; Fischer et al. 1990; Wouters and Rosario-Chirinos 1992).

Apart from the single fiber IR method proposed by Martoglio et al. (1990), all these procedures require extraction of the dye from the fiber. Until now, researchers have extracted dyes in strong acid solutions. With heat, the hydrochloric or sulfuric acid solutions quickly release the dyes from the fibers. At the same time, the acid also quickly destroys protein and cellulosic fibers as well as some of the dyes. Because of the need to balance the level of destruction with the amount of information obtained when examining historic textile materials, emphasis has been placed on reducing the size of specimens.

The extraction method described below, using ethylene diamine tetraacetic acid (EDTA) and N,N-dimethyl formamide (DMF), extracts sufficient dye from 2 mg specimens for spectral detection and identification yet leaves wool fibers intact for further investigation. The effectiveness of the method is compared with the water/methanol/hydrochloric acid (HCl) extraction method developed by Wouters and Verhecken (1989b). Concentrations of the yarn extracts are measured with the photometry function on the UV-VIS spectrophotometer. Also, the absorbance curves for madder, Relbunium, and cochineal after EDTA/DMF extraction are shown to be readily distinguishable for identification purposes. The effect of the EDTA/DMF treatment on wool fibers is assessed by tensile testing and microscopic examination of the fiber surface.

The EDTA/DMF extraction method is also tested on red fibers taken from the collection of ancient Peruvian textiles in the Krannert Art Museum, University of Illinois, Champaign. The dyes are identified by UV/vis spectrometry. Microscopic examination reveals that the fibers remain in good condition after extraction.