Raku was invented in the 16th century, because workers wanted to make tea bowls fast on a construction site. 

 By taking the ceramics out of the kiln at the highest temperature, the glaze starts to crackle due to the dramatic temperature change. By covering it in sawdust, the sawdust starts to burn and smoke, but also sucks up all the oxygen. The reduction of oxygen sucks up all the leftover oxygen in the minerals of the clay, turning the un-glazed clay black, And burning sawdust leaves its soot. 

 

Since then, people have been experimenting with Raku firing. Using hairs, newspapers, plants and glazes that react with oxygen.