The deterioration of 34 historic silks from 1850-1930 was first documented by a visual rating scale (Deterioration Rating Scale, DRS) patterned after the deterioration rating used in library surveys. This was followed up by photographs of the fabric surface and with microphotographs of the fibers. Surface fabric deterioration corresponded with fiber deterioration at the microscopic level. Presence and type of weighting was determined by scanning electron microscopy with energy dispersive x-ray spectrometry, by neutron activation analysis, and by inductively coupled plasma analysis. Light colored silks contained tin and dark colored fabrics contained iron, in amounts greater than 10, 000 ppm. Terbium (greater than 200 ppm) and arsenic (greater than 500 ppm) were present on several samples. The most severely deteriorated samples rated 4 or 5 on the surface) contained greater than 50,000 ppm tin or iron. Application of eight preservation formulations to historic silks showed that only a deacidification agent (Wei T'o) and the ultraviolet absorber Cyasorb 531 resulted acceptable color change levels. Color change on historic silks was dependent on original fabric color. All treatments produced some color change. Wei T'o and peroxide decomposer Cyanox STDP produced less change on light colored samples than on dark samples; peroxide decomposer Mark 260 and chain breaker Cyanox 1790 were acceptable for dark colored samples. Tests on new silk indicated that only Cyasorb 531 retarded yellowness and decreased tensile strength. The other antioxidants retained strength but increased yellowing the deacidification agent retarded yellowing and was without effect on strength. No synergistic effect was found on yellowing; but Cyasorb 531 and Cyanox 1790 appeared to be synergistic with respect to tensile strength.