THE DETECTION OF METALLIC MORDANTS BY ENERGY DISPERSIVE X-RAY SPECTROMETRY
R.J. Koestler, N. Indictor, & R. Sheryll
3 RESULTS AND DISCUSSION
TABLE ILISTS THE TEXTILES AND ACQUISITION numbers of the silk textiles studied. The color of the fiber taken from each textile is also given and the elements found are shown in descending order of abundance. Each sample showed the presence of sulfur as would be expected from silk.6 The level of sulfur appears to be slightly lower than that found in modern undyed mordanted samples examined in earlier studies5 with the exception of B-5-a and B-5-b. It is possible that this is the effect of aging (loss of sulfur) or the effect of dyeing or mordanting. The observed weight percent of any element will obviously decline in the presence of added matter. The weight percent in all samples reflects only weight percent of elements above the atomic weight of fluorine and not the weight present in the sample. The brown and gray fibers appeared to have significantly less sulfur than the other colored fibers. Lowered sulfur content of proteinaceous fibers has often been associated with aging.7Table I also indicates the presence, at least in trace amounts, of aluminum and iron in all fibers except B-5-b, undyed.
Table I Historical Silks: Results of EDS Scans
The judgment as to whether the aluminum or iron has been used as a mordant or was present from some other source was tentatively based on the ratio of metallic element to sulfur rather than the absolute value of the element (Table II). A similar procedure was used sucessfully for mordanted, dyed modern wool samples on which sulfur was also used as an internal standard (see Part I). A “yes” entry was made for aluminum when the ratio of aluminum to sulfur was ca. 2:1; a “?” was entered, possibly present, when the ratio of aluminum to sulfur was ca. 1:1; “(-)”, probably absent was entered when the ratio of aluminum to sulfur was less than 1:1. For iron “yes” was entered when the ratio was much greater than 2:1; a “?” was entered when the ratio was ca. 2:1; “(-)”, probably absent, was entered when the iron to sulfur ratio was ca. 1:1; and “-” was entered when the iron to sulfur ratio was less than 1:1. It may be observed that the brown colors were achieved in more than one way (cf. B-2-c, B-3-c iron mordant; and B-4 probably neither aluminum nor iron). Finally it may be observed that calcium was present in very substantial quantities in all samples. It was usually the most abundant element indicating the possible presence of calcarious material associated with the surface of the textile. A group of mordanted (undyed) modern silks studied previously as standard also showed substantial calcium in EDS scans but approximately half the amount observed in the sample decribed here. The consistently high percentages of silicon in the scans indicates the presence of siliceous materials as well. The presence of iron and/or aluminum associated with the siliceous or calcarious material rather than as mordant cannot be excluded; nor the trace presence of aluminum and/or iron associated with some additive (e.g., sumac or tannin, as discussed at some length in ref. 1). It should also be added that sulfur as part of the proteinaceous backbone and sulfur as adventitious material (mordant, salt, soil, etc.) cannot be distinguished.
Table II Presence of Metallic Mordant on Historical Silks
The foregoing technical information illustrates some points made in the introduction. Authentication of the materials under discussion is not possible based on the data obtained. However none of the elements detected suggests a technology in the mordanting procedures at odds with analyses of other archaeological material.8 In order to demonstrate a late date for these textiles further analyses would be required. Since the technology is now available to do mordant analyses, dye analysis, and C-14 dating on micro-samples it would be a valuable contribution to the study of textile technology to continue this investigation.
We plan to enlarge our study of mordants on historical textiles; we are also planning a study of metallic yarns and weighted-silk fabrics.