•The secret to cool bodies and glazes is alot of testing.
•The secret to know what to test is material and chemistry knowledge.
•The secret to learning from testing is documentation.
•The place to test, do the chemistry and document is an account at https://insight-live.com
•The place to get the knowledge is https://digitalfire.com
The raku process is an economical way of firing ware in reduction to achieve metallic and carbon effects. Normally ware is heated in a kiln until the glaze is melted to the desired degree then it is removed with tongs and put into a container of organic material (i.e. sawdust) where it is cooled. The organic material burns and uses the available oxygen in the container and the metallic effects develop. Because of the heat shock during heat-up most people bisque fire ware before rakuing.
Raku ware is usually crazed and very porous and lacking in strength. Thus it is only suitable for decorative ware. Metallic effects that looked great out of the firing can tarnish and disappear with time and people have developed ways to preserve these with various fixatives and surface treatments.
Raku firings often generate a lot of smoke, an people have developed different ways to try to contain this smoke. Unfortunately some have developed and even promoted quite casual methods that pose significant dangers. Raku kilns can emit harmful metal fumes (depending on how pots are decorated) and vapors of chlorine and sulfur (from salts, chlorides, and sulphates). Some people have been seriously injured in this regard.
Inhalation of Chlorine can cause chemical pneumonia, immune reactions, rashes, irritated mucous membranes, diarrhea, nausea, vomiting, cancer, brain damage, etc. Smoke from raku is hazardous simply because ALL smoke is hazardous and possibly carcinogenic. Incomplete combustion ("yellow" smoke) produces the most hazardous substances in smoke (i.e. wood tar and thousands of other compounds). While some people claim to wear respirators with "smoke blocking filters" there is no such thing. This is why firefighters wear tanks of compressed air.
Texture of a typical raku body after throwing
This is Plainsman Raku. It has 18% 35-65 mesh grog, 65% Plainsman A3 buff stoneware clay, 14% Pyrax and 3% bentonite.
By Tony Hansen