Heavily grogged clay fired to 1000c.
Snatched from the kiln in their molten state.
Plunged into an oxygen starved bin and covered in sawdust.
The sawdust needs to burn in the intense heat generated by the piece.
To burn it extracts oxygen from the glaze oxides to produce amazing metallic colouration.
Raku is the process of firing pottery in a raw uncontrollable way. The bisque ware ( already fired once to ensure a chance of the pottery surviving the shock of extreme heat) is glazed and then placed in the cold kiln. Within an hour it is heated up to 1000c and then removed from the kiln as if from an open volcano. Truly exciting, slightly dangerous and spontaneous.
You can influence whether the glaze is oxidised or reduced through the use of the sawdust and air sealed bins. But you can't predict the outcome entirely. . . . and that is why it is such fun!