7 SUMMARY AND CONSERVATION IMPLICATIONS

Biochemical characterization of a proteinaceous textile, particularly silk, not only identifies the major constituents of the fabric but also indicates the state of preservation of the material. All the historic fabrics exhibited some degree of degradation, as evidenced by their solubility in denaturing conditions and the composition of the solubilized degradation products. An overall decrease in all the amino acids recovered, particularly tyrosine, can be used to relate a historic silk to artificially aged fibroin. Once an artificially aged sample, comparable to the actual object, has been prepared, it can then be used in lieu of the object in the evalution of prospective treatments.

The compositional data from the silk fabrics of the First Ladies Collection revealed two populations; sericin-rich and sericin-depleted materials. These two populations present different concerns to the conservator. While sericin yellows easily, it protects the fibroin filaments against light damage as exhibited by the state of protein preservation of the sericin-rich fabrics. The naturally aged fabrics that retain a sericin coating are at great risk of losing that protective coating with any wet treatment. Conversely, the sericin-depleted fabrics are more likely to have already suffered severe light damage, and their increased solubility is a result of actual fibroin loss. Any conservation treatment that involves washing sericin-depleted fabrics not only jeopardizes the integrity of the object but provides an opportunity for further light damage to the newly exposed fibroin.

The analytical techniques described require an extremely small amount of fabric that can easily be sampled from the unfinished edge of an inside seam. Spot treatments of fabrics to be cleaned with any solvent can be examined for material removed in the washing solution. Amino acid analysis of the cleaning solution can determine not only how much material is lost but also the nature of the protein being removed. The aggregate data from the analysis of the First Ladies costumes indicate that silk fabrics manufactured in this century are likely to have been extensively processed, resulting in a complete loss of the sericin coating. This processing puts these recently produced fabrics at extreme risk for light damage.

ACKNOWLEDGEMENTS

This study was funded by a Smithsonian Pre-Doctoral Conservation Science Fellowship (M.A.B.) in conjunction with the Johns Hopkins University.