|Monthly Tech-Tip |
Made at Alberta Clay Products in Alberta, Canada about 1960. These are massive. They were hand-constructed. This was fired in a beehive kiln and is on display inside one next to the Plainsman Clays plant (a historic site). Ceramic glazes are normally slurries of clay, quartz and and fluxes like sodium feldspar, calcium carbonate or dolomite - these are applied to ware before firing. But, in this salt-glazing process, common table salt was literally shovelled into a hole at the top as the kiln reached temperature (about 2350F)! The salt decomposed, separating into sodium vapour and chlorine gas within the chamber and the sodium reacted with the quartz-containing clay to form a durable glaze. Unfortunately the chlorine gas escaped into the air!
This was built just after the turn of the 20th century and was one of about 25 at the Alberta Clay Products company. It was used to fire salt-glazed ceramic pipe, these were used for municipal sewer and water lines. A ceramic industry quickly grew in the city because it had good clay, natural gas, plenty of water, a dry climate, industrious people, a large river and it was on the Trans Canada highway and railway.
Salt firing is a process where unglazed ware is fired to high temperatures and salt is introduced to produce a vapor that glazes the ware.