technical information for potters
On this web site there are several pages of C6 oxidation glaze test tiles photos with recipes, several pages of Cone 10 Reduction soda/salt glaze and engobe tiles and recipes, several of cone 10 Reduction gas firings, one page of oxide washes and one page of soda/salt clay bar tests. Please note that there are several C10R glaze recipes in the soda/salt pages.
Some recipes in these tests are of my own formulation, some from the vast Clayart Archives, friends and other sources, long forgotten.
***PLEASE NOTE: None of these glazes have been tested for leaching or durability. They are presented "AS IS". Many are preliminary tests, some of which will need reformulation and retesting. Some of my clear base tests show crazing on the porcelain tile, which I will have to correct. The same glaze worked OK on a white stoneware (B-Mix) so it will need a bit of tweeking to make it work as well on the porcelain. Usually, just a small addition of silica and clay will fix the problem of minor crazing. Also, worth noting, is that most of these tests which contain gerstley borate were made with an older batch of gerstley, when it had more boron content and less magnesia. These same glazes made today, with current gerstley, may not be quite the same. Gerstley has been such a variable material over the years, that new batches often required reformulation of existing glazes.
The Cone 6 OX Glaze tiles were fired were fired manually in an Aim test kiln. The firings ranged from 12-15 hours, some with a bit of a firing down. Most were fired to a large cone 6 touching; but a few were in an earlier firing using only a small cone 6 bar cone. All future C6 firings will be to a large C6 cone touching.
The Cone 10R glazes and C10 R soda/salt firings were fired in a 17cu ft Geil, fiber kiln, usually in a 12-15 hour schedule with reduction beginning quite early (around 1550-1600F), alternating the reduction from light to fairly heavy periods, usually to C10 between 1 and 5pm. Exceptions may be noted.
The clay bodies used on the C 6 OX tests were mainly Laguna's B-Mix and Highwater's P5 porcelain. The clay bodies used in the C 10 R glaze tests were all west coast clays, mainly from Laguna in S. California, or Georgie's in Portland, Oregon.
Some glazes were designed or tested out of my own curiosity or my specific requirements, which may or may not be intended for functional use. These photos will give those firing at C6 oxidation some of the possible color and surface choices available in this range.
***WARNING: Many glaze materials are toxic, so use good studio safety practices when handling all raw materials and be well versed in the toxicity of the various materials used in glaze formulation, as well as their proper handling. And, keep in mind, although you may not design something to be used for food, the person who purchases that pot, or receives it for a gift, may decide that that pretty vase with a non-functional glaze would be nice to store and serve liquids.
Also, it is strongly recommended that you have functional glazes tested for safety. This can be done reasonably through Alfred University. More information can be obtained through the Clayart archives at http://www.potters.org/categories.htm or by calling or emailing Alfred University.
LINKS FOR CLAY AND GLAZE TESTS, GLAZE AND OXIDE WASH RECIPES