Alkaline oxidation method. The black spots on the surface can be removed by alkaline oxidation. The alkaline oxidation method is called high-temperature oxidation method. It is carried out under higher temperature conditions in a sodium hydroxide alkaline solution containing a certain oxidant. The oxidant interacts with the metal iron to form an oxide film mainly composed of magnetic iron oxide. Can effectively remove black edges. Rice roll originated from Luoding, Guangdong and is one of the famous traditional snacks in Guangdong.