Pots are prepared with a smooth the surface, terra sigillatta applied, burnished and bisqued to ^09. Then, various salts are applied to the surface. Such chemicals include Ferric Chloride, Potassium Dichromate, Copper Sulphate, Iron Sulphate, table salt, epsom salts, miracle grow of various types. Saturated mix of 100 grams of chemical to 1 pint of hot water. Many of these chemicals are hazardous. Follow precaution according to MSDS. Use Nitril gloves and the correct respirator for vapors. Other combustibles can be added such as horse hair, wire, seaweed, lemon or orange peels. The pot and additives are wrapped like campfire potatoes using a double layer of heavy duty aluminum foil being careful to seal it tightly. Fire the kiln up to anywhere between 1200 F to 1450 F. When you see the foil is dull rather than shiny, possibly puffed up, it is done. If you over fire the foil, the colors may be lost. You can re-apply the colorants and fire again..
I have lowered my firing temperature from 1450 to 1350 F max. it could be my pyrometer reading. Trying to avoid the breakdown of the aluminum foil. I did a project to develop a palette with more colorful range. These test tiles will be applied to new work July 25 or so. Here are the results fro my color tests. Chemicals were Copper, Cobalt, Iron, Manganese, chrome in the form of sulphates, chlorides and nitrates plus sodium and potassium nitrates. Minuscule amounts of 6.5 grams were mixed in a 1/8 cup of water. 5 various rows with three tiles with the same colorants fired at roughly 1175 F, 1250 F and 1350 F.
Using Ceramic Saggers the temperature can go hotter. Also Not using a sagger can go hotter as well but the fumes may contaminate the kiln.
The tiles are marked roughly. Three circles of cases were Barium, Calcium and Magnesium chloride. Hoped to see if these fluxes would effect the metallic colorants as they do in a glaze. calcium seemed to do that the most. A cross of copper nitrate was across the tile. Edited notations:
temperature variations were significant on Nickel and Cobalt Chloride and Copper Sulphate
Halos develops between nitrates and chlorides. Blushes worked well between Chlorides and sulphates
White dots were from epsom salts and more colorful lighter dots were strontium chloride crystals
Yellow developed w/ Calcium Chloride and Sodium Dichromate
nice aqua blush w/ sodium dichromate , Copper Nitrate and Cobalt Chloride
Cobalt, Copper and Nickel chloride need higher saturation
Color in chlorides weakened in higher temperatures. #foilsaggar,#alternativefiring,#nakedclay,