Study of the microstructure of silk artifacts recovered from a historic deep-ocean site

A comparative study of the microstructure of three marine silk textiles recovered from the site of the S.S. Central America, reference silk fabric, and three historic silks from the same era as the marine textiles was conducted. The analytical techniques used include optical microscopy, scanning electron microscopy, energy dispersive x-ray spectrometry, x-ray diffraction, infrared microspectroscopy, and differential scanning calorimetry.; Results indicate that the physical microstructure of two of the marine silk artifacts has been altered significantly. An increase in fiber diameter was observed in these two marine silks and their gross physical structure was considerably damaged. Crystallinity indices obtained from IR and XRD are lower in all of the marine and two of the historic silks in comparison with reference silk. Specimens vary in the extent to which short- and long-range order have been disturbed as a result of age and/or marine exposure. In all marine silks and two historic silks, the glass transition is suppressed and degradation temperature altered. Crystallite size perpendicular to the intersheet- and interchain-directions, and the unit cell dimensions, have not altered appreciably in any of the specimens. The primary effect of marine exposure appears to be conversion of some of the crystalline phase into an ordered-amorphous structure. Additionally, the amorphous phase is partially dissolved or recrystallized to an ordered-amorphous phase. No qualitative alteration of the chemical microstructure of fibroin was observed. Organic and inorganic surface deposits are observed on the marine silks but these are not as extensive on the historic artifacts. The formation of biofilm is observed on both the historic and marine silk, but to varying extents.; Applicability of the analytical tools to analyze rare artifacts is addressed. While basic analytical studies are important in understanding the structure and degradation of rare artifacts, once understood, subsequent work should build on this research and employ techniques which require smaller samples. From a conservator's perspective, the results indicate that the marine silks are more susceptible to degradation than are historic silks. Handling and storage treatments should focus on controlling the environment and on treating the artifacts to minimize subsequent degradation.