POLISHING TO REVEAL MICRO-DEFECTS ON GLASS

There are a great many imperfections on polished surfaces, ranging fro m micro-defects to macro-defects. This report deals with micro-defects on polished optical glass and a method to reveal them. First, zirconi a ceramic workpieces and optical glass workpieces were polished. It sh ould be noted that, they were polished smooth with abrasive powders wi th superior ability to remove material, but when polished with abrasiv e powders with inferior ability to remove material the surfaces turned rough with defects such as digs or pits. It was observed that in glas s polishing the mechanical actions of large abrasives and dusts do not make such defects but rather scratch the surface. There was, however, some possibility that the scratch changed into digs or pits as polish ing advanced. Then, taking these results into account, a new polishing condition was proposed using silicone oil instead of the usual abrasi ve slurry to reveal micro-defects at the surface of glass. For example , it was shown that there are 10-30 micro-defects in a square millimet er or 32-165 micro-defects in a cubic millimeter of a dense flint glas s including cadmium.