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Salt, soda firing

Salt firing is a process where unglazed ware is fired to high temperatures and salt fumes are introduced into the kiln chamber (normally by a spray in the burner ports). The sodium in the salt combines with the silica and alumina in the clay to form a vapor cloud that glazes the ware. Salt glazed ware often has marbled and variegated surface effects and has a very distinctive look. Salt glazed ware is suitable for functional use.
Sodium vapor glazing using compounds other than sodium chloride (table salt) is practiced by many people. Many books are available on this topic and an increasing number of web pages on the Internet extol the process.
There has been quite a bit of discussion about the safety and environmental concerns of salt vs. soda firing. It does not appear to be a foregone conclusion that soda is better than salt or even that chlorine is released in salt firings (rather than HCL vapor). Recent reports on the Internet claim that measurements done on kilns have demonstrated that salt firing is as clean or cleaner than fuel reduction firing.

Small cone 10R salt glazed test piece

Plainsman P580, P600, H570 soda fired samples

These fire ivory to bone with in reduction.

Salt glaze beehive kiln beside the Plainsman Clays plant

This was built just after the turn of the 20th century and was one of about 25 at the Alberta Clay Products company. A ceramic industry quickly grew in the city when it was discovered that it had the magic ingredients: Good clay, natural gas, plenty of water, a dry climate and industrious people.

Salt glazed sewer pipe and fittings

Made in southern Alberta around 1960. They were extruded and then hand assembled.

Soda and salt kilns at the Medalta International Artists in Residence

In Medicine Hat, Alberta, Canada. Designed by Aaron Nelson.

Rear of soda and salt kilns at the Medalta International Artists in Residence

In Medicine Hat, Alberta, Canada. Designed by Aaron Nelson.

A salt glazed mug fired at cone 10 in the kiln at the Medalta artist in residence program

Crazing in glazes is common in this type of ware but since the body is fired well into vitrification this is not considered an problem (the unique aesthetics of this type of ware trump such issues). Salt glazes, by their very nature, are high in sodium. And it has a high thermal expansion.

Salt glaze pipe fittings

Made in southern Alberta around 1960. These are massive. They were hand constructed.

A salt kiln being unloaded

Notice how ware is set on pads of clay to enable the salt vapours to access the underside. Salt and soda kilns degrade over time as the sodium eats away at the interior bricks. Shelves must be covered in kiln wash to preserve them.

In Bound Links

  • (Glossary) Firing

    At it most basic level, firing is process of heati...

  • (Glossary) Flashing

    A fired visual effect on bare clay surfaces in fue...

By Tony Hansen

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