Metallic weighting agents, especially tin and iron, cause rapid degradation of silk, leaving many artifacts in very fragile condition. To aid in the identification of weighted silks, three tests were evaluated on 18 unknown silks: a burning test, a flame test for tin, and a spot test for iron. These tests gave consistent results, verified by energy dispersive x-ray analysis. The effects of ultraviolet and visible light on new unweighted and tin-weighted silk was studied. Tin-weighted silk showed consistently greater degradation than unweighted silk when exposed to ultraviolet plus visible light. Under visible light only, damage was greatly reduced; however, significant changes in the weighted silk still occurred.