Proper selection of glass sheet before glass processing is very important. A defective glass sheet may lead to quality issues and shattering during the process. Avoid using a glass sheet containing stones. Especially in the tensile stress area, even tiny stones could become the cause of spontaneous glass breakage. Because the expansion coefficient of stone is different from that of glass, cracks can appear around the stones. This is the weak area of the glass, also known as the stress concentration area. When tempered, the stress effect multiplies, causing the glass to break spontaneously. The location of the stone is a very important factor. If the small stone is located in the compressive stress layer, it may not cause glass breakage even with a size of 1mm. However, tests indicate that tiny stones smaller than 0.1mm will indeed break all samples when they are located in the tensile stress layer. This is because the cracks around the stone expand much faster in the tensile stress area than in the compressive stress area. As a result, the proper selection of glass sheets is a key factor to ensure the high quality of the glass after tempering.