The Glaze That Comes from the Air

Salt firing and soda firing are atmospheric glazing techniques. Instead of applying glaze to each pot individually, the glaze is introduced into the kiln atmosphere during firing and deposits itself on every surface inside the kiln simultaneously: pots, shelves, kiln walls, and all.

Salt Firing

In traditional salt firing, common salt (sodium chloride) is shovelled or thrown directly into a gas or wood kiln at peak temperature (typically around cone 10-11).

At that temperature, the sodium vaporises and reacts with silica and alumina in the clay body surface, forming a thin, skin-tight sodium silicate glaze directly on the clay. The result is:

• A distinctive orange peel texture: a fine, slightly dimpled surface that is unlike any brushed or dipped glaze.
• Extremely tight fit between glaze and clay: the glaze is part of the clay body surface, not a separate layer.
• Chlorine gas is a by-product of the reaction. Salt kilns must be fired outdoors or with heavy-duty fume extraction.

Soda Firing

Soda firing uses sodium bicarbonate or sodium carbonate (soda ash) instead of salt. The surface effects are very similar (the same tight fit and organic texture), but:

• No chlorine gas is produced, making soda firing safer and more environmentally acceptable.
• Soda is typically introduced dissolved in water and sprayed into the kiln through ports.
• The surface texture tends to be slightly smoother than traditional salt.

Did You Know?

Salt glaze pottery has a rich history dating back to 15th-century Germany, where the technique was used to produce the distinctive Bartmann jugs of the Rhineland. The characteristic orange-peel texture of salt and soda glazing is a direct result of sodium vapour reacting with the silica in stoneware clay bodies at high temperature.

Practical Decision: Salt or Soda?

Choose based on your studio constraints:

• Pick salt if your setup supports strict fume control and you want classic strong orange-peel character.
• Pick soda if you want similar atmospheric effects with safer emissions and finer control via spray introduction.

Pro Tip

Run side-by-side test loads with identical clay and slips in both methods. Direct comparison will teach more than theory in one cycle.