Tea bricks from the 19th century are very rare: it is the nature of this kind of currency to get consumed over time. Incidentally, this is the great advantage of every kind of bar currency – that it can circulate as money as well as being used for its material. The value of tea bricks depends on the quality of the tea. Poorer-quality tea is often optically corrected by adding a little soot to give it a richer color. Other price factors are the quantity available and the distance from the market. In Mongolia around 1900, 12 to 15 bricks of good quality tea would buy a sheep.