After the optical lens is finely ground by the grinding liquid, there is a crack layer of about 2-3m thickness on the surface, and the method to eliminate this crack layer is polishing. The mechanism of polishing and grinding is the same, only the tool material used is different from the slurry. The materials used for polishing include cloth, polished leather and pitch, and the polishing surface with high precision is usually achieved. The most commonly used material is high-grade polished asphalt.

The use of asphalt to polish, through the fine surface of the asphalt, drive the polishing liquid to grind the surface of the lens to generate heat, so that the glass can melt and flow, melt the rough vertex and fill the bottom of the crack, and gradually remove the crack layer. At present, the polishing powder used for polishing glass lenses is mainly cerium oxide (CeO2), and the proportion of polishing liquid is different according to the different polishing period of the lens. Generally, the polishing liquid with higher concentration is used when the polishing mold is combined with the polishing mold in the early polishing stage. After the surface of the lens is bright, the polishing liquid with thinner concentration is used to avoid the orange peel phenomenon of the mirror (the lens surface atomization).

The motion mechanism used for polishing and grinding is the same, in addition to the polishing tool and the working liquid are not the same, the environmental conditions required for polishing are also more severe than that for grinding. General polishing matters to pay attention to are as follows: polishing asphalt surface and polishing liquid can not have impurities, otherwise it will cause mirror scratching. The surface of the polishing asphalt should be consistent with the surface of the lens, otherwise it will beat when polishing, so it will bite the polishing powder and scratch the surface of the lens.

Before polishing, it must be determined whether the surface of the lens is scratched or punctured after grinding. Whether the size and material of polishing tools are appropriate. Whether the hardness and thickness of asphalt are appropriate. In the process of polishing, we must always pay attention to the condition of the lens surface and check the accuracy. The inspection of lens surface defects, because the inspection process is judged by personal vision and method, the inspector should have a deep understanding of the specifications of scratches and sand holes, and often compare the standard sample of scratches and sand holes to ensure the correctness of the inspection.