Try sprinkling salt, lithium, or low melting fluxes such as colemanite borax, or frits, around the pieces as you pack the kiln. Again, it is advisable to use bisqued-ware. THE KILN Sawdust kilns are usually built with common house bricks. The size depends on the number and size of the works you wish to fire. A common size is a box about 80 cm cubed.
Metal drums function quite well as sawdust kilns- at least for a few firings.
Packing the kiln Begin with 10-15 cms of sawdust on the floor. To avoid the strong black marking on the underside of the packed piece, place it on a brick in the kiln with no sawdust between them. Most artists in this field tend to place pieces on their sides or upside down to take advantage of this fact. Pour sawdust around the pieces, ensuring that the topmost work is covered by at least 10 cm of sawdust. Some people like to fire only one piece at a time, building the kiln to size each time, and leaving 5-10 cm between the piece and the walls of the kiln.