First of all, you can touch the surface of the bone china cup with your hands to see if there is any unevenness. If you feel the unevenness and you can see the uneven surface of the color with the naked eye, then it is overglaze. Because this kind of product is pasted on the glaze surface with flower paper made of ceramic pigments or directly painted on the surface of the product, because the firing temperature does not reach the melting temperature of the glaze layer, the flower surface cannot sink into the glaze, so there is lead. It is possible to exceed the standard, it is best not to buy. If the surface of the product is visually smooth, has glass luster, and no uneven patterns can be touched, then it should be in-glaze or under-glaze color. In-glaze color is the color firing temperature of ceramics reaches the melting temperature of the glaze, and the ceramic pigment sinks into the glaze when the glaze melts, and is covered by the glaze layer after cooling. Since the pigment does not directly contact the food, it is safer to use. And all the decorations of the underglaze color are carried out on the porcelain body, and then fired once after being glazed, so it is also very safe.