Optical glass is finely ground by the grinding liquid,  optical glass surface has a crack layer for 2–3 m thickness, so the method of eliminating the crack layer is for polishing. The mechanisms of grinding and polishing are the same, except for the tool material is different from the polishing solution. The polishing materials are for cloth, polyurethane and pitch. If for polishing surface with high precision, common material is for advanced polishing pitch.

    If polishing with pitch,because of the pitch fine surface, which drives the polishing liquid to grind the glass surface  to heat, so that the glass melting and flowing, melting the rough apex and filling up the bottom of the crack, and gradually removing the crack layer. At present, the polishing powder is mainly for cerium oxide (CeO2), and the proportion of the polishing liquid is different depending on the polishing cycle . Generally, the high concentration polishing liquid is used at the beginning of polishing .After the glass surface is bright, use a rare polishing solution to avoid the glass surface atomization.

   The movement mechanism of polishing and grinding are same. Except for the polishing tool and the working fluid are different, the working environment in polishing is with more rigor than grinding. Generally, the announcements when polishing are as following:  no impurities in the surface of the polishing asphalt and the polishing liquid, otherwise the glass surface will be scratched. The surface of the polished asphalt should conform to the glass surface, otherwise it will be easy to bounce during polishing, therefore biting the polishing powder and scratching the lens surface.

   Before polishing, we should confirm whether the lens surface has scratches or punctures or not. And with the size and tools for polishing materials are suitable. And the hardness and thickness of  asphalt are proper. We should pay attention to the glass surface and accuracy checking during the polishing process. Inspection of the lens surface, because the process of detection is judged by personal vision and methods, the inspector should have a deeply understanding for scratches and sand holes, and often compare the standard patterns of scratches and sand holes to ensure the testing accuracy.

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