POLISHING TO REVEAL MICRO-DEFECTS ON GLASS

There are a great many imperfections on polished surfaces, ranging from micro-defects to macro-defects. This report deals with micro-defects on polished optical glass and a method to reveal them. First, zirconia ceramic workpieces and optical glass workpieces were polished. It should be noted that, they were polished smooth with abrasive powders with superior ability to remove material, but when polished with abrasive powders with inferior ability to remove material the surfaces turned rough with defects such as digs or pits. It was observed that in glass 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 polishing advanced. Then, taking these results into account, a new polishing condition was proposed using silicone oil instead of the usual abrasive 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 millimeter or 32-165 micro-defects in a cubic millimeter of a dense flint glass including cadmium.