"cr-39 is transparent in the visible spectrum and is almost completely opaque in the ultraviolet range. it has high abrasion resistance, in fact the highest abrasion/scratch resistance of any uncoated optical plastic. cr-39 is about half the weight of glass with an index of refraction only slightly lower than that of crown glass, and its high abbe number yields low chromatic aberration, altogether making it an advantageous material for eyeglasses and sunglasses. a wide range of colors can be achieved by dyeing of the surface or the bulk of the material. cr-39 is also resistant to most solvents and other chemicals, gamma radiation, aging, and to material fatigue. it can withstand the small hot sparks from welding, something glass cannot do. it can be used continuously in temperatures up to 100 °c and up to one hour at 130 °c."