CR-39 is transparent in 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 and index of refraction only slightly lower than that of
crown glass, making it an advantageous material for eyeglasses
and sunglasses lenses. 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 of solvents and other chemicals, to gamma
radiation, to aging, and to material fatigue. It can withstand
the small hot sparks from welding. It can be used continuously
in temperatures up to 100 °C and up to one hour in 130 °C. In
the radiation detection application, raw CR-39 material is
exposed to proton recoils caused by incident neutrons. The
proton recoils cause tracks, which are enlarged by an etching
process in a caustic solution of sodium hydroxide. The enlarged
tracks are counted under a mi