In a message dated 9/25/2003 1:46:52 PM Pacific Standard Time, FloodJR@NV.DOE.GOV writes: True. At one time, thorium oxide was widely used in manufacturing glass to change the index of refraction for microscope and camera lenses. However, it hasn't been used for this in decades. Actually, there are still optics firms that coat lenses with thorium for certain customers. Barbara