Inkstones (or ink slabs) are vessels in which ink is ground with an ink stick. Chinese invented the ink stone. Inkstones are manufactured from stone, clay, bronze, iron, and porcelain. They have a smooth flat surface to grind the ink stick into liquid ink and to this purpose they created an ingenious grinding tool - the inkstone.
Táo(hé)yàn) are made from the stones found at the bottom of the Tao River in Gansu Province. These inkstones were first used during the Song Dynasty and became rapidly desired. It bears distinct markings such as bands of ripples with varying shades. The stone is crystalline and looks like jade. These stones have become increasingly rare and are difficult to find. It can easily be confused with a green Duan stone, but can be distinguished by its crystalline nature.
The very fine mud under the bed of the Fenhe River is filtered, mixed with bounding material, dried and carved into inkstone, then fired in the kiln. Because of the different minerals in the mud and also the different temperature of the firing, final products have different colors.