Kiln Atmosphere

Kiln atmosphere refers to the chemical contents of the air inside the kiln.

Oxygen / Carbon Monoxide

Aside from electric, kilns are heated by burning hydrocarbons.

If the combustion is complete, the end products are carbon dioxide and water. This is called oxidation
If the combustion is incomplete, the firing produces carbon monoxide
- This is called reduction
- The carbon monoxide reacts with metal oxides in the clay body and glaze
  - The metal oxides are reduced
- The intensity of the reduction affects the appearance of glazes
Heavy reduction can be "sooty", producing pure carbon

Sodium carbonate is dumped / sprayed into the kiln
- The sodium carbonate vaporizes and sodium reacts with the clay and glaze
- High Alumina Clay will show Alkali Flashing
Salt firing is similar but uses rock salt (NaCl)
Some potters use a mix of sodium carbonate and sodium borate

I think it should be possible to perform a controlled version of soda firing by dipping pots in a sodium carbonate solution

Wood is used as the fuel source, often pine because it can burn very hot and efficiently
Wood ash is often deposited on the surface of pots
- Ash can be eliminated by firing in saggars
- Deposited ash can form a natural glaze - some potters leave pots unglazed, fully exposed to the effects of ash
- Wood ash is primarily made of calcium and magnesium along with some iron

Created 2024-04-06.