What makes the raku pottery process different from others such as stoneware? Both the clay used and the glazes as well as the firing process itself.
Technically speaking, any type of clay – referred to as ‘clay body’ by those who work with clay – can be used in the raku firing process (though not all can be used successfully) and the clay itself generally matures at a higher temperature than that of the raku firing; raku pieces are pulled from the firing (red hot) when the glazes appear to have matured. The temperature range for raku firing is between 1860-1900, depending on glazes used and other factors such as how many pieces are being fired together, ambient temperatures outdoors – to name a few. Not all clay bodies can stand up to the expansion/contraction experienced in raku firing, therefore, not all clay bodies can successfully be fired this way without cracking or otherwise self-destructing; i.e. porcelain.
Through trial and error, I selected and now work exclusively with a clay body by Laguna Clay specifically formulated for the raku process. This clay matures, or becomes ‘vitreous’ (non-absorbent) at a much higher temperature than that of the raku process, therefore it does remain porous post firing. Raku art pieces are fired all year here at my studio facility in Western Colorado and in January, when the temperatures can be as cold as 5-25 degrees F, perhaps you can begin to sense the importance of working with a clay body which can withstand the dramatic temperatures between being pulled at around 1860 F and removed into frigid air temps of 5 F….that’s a huge jump!
The glazes I use in raku firing differ from those used for functional ware (i.e.: mugs, bowls, plates, etc.) in that they contain metallic colorants which results in raku ware being for decorative purposes and not for use with food.
Other than the type of clay, glaze and the firing process itself, the methods of making clay forms are the same as any other work with clay; pieces are created via wheel throwing, slab construction or hand building (and other variations).