Cupel is usually made of magnesium oxide (sometimes incorrectly called magnesium), ashes, Portland cement and other materials. In the fire test process, ash blowing is the last and most important step. Therefore, the quality of the cupel is extremely important.

In the process of ash blowing, lead is oxidized to lead oxide (PbO), most of which are absorbed by the cupel. Gold, silver, platinum and other precious metals form a grain in the cupel. Then the particles are used to determine the content of their precious metals.

In gold and silver tests, the typical cupellation furnace temperature is 900 to 1000 °C, but it can vary with technology, air flow rate, and cupel materials. The magnesia cupel produced by Qingdao Kingpro Advanced Material Co., Ltd. has the characteristics of high refractoriness (≤1100 °C), fast absorption, 97% - 98.5% recovery, easy to use, no need to grind edges and no cracking during the shelf life.