ACP massive salt-glazed sewer pipe junction

Made at Alberta Clay Products in Alberta, Canada about 1960. They were hand-constructed. This was fired in a beehive kiln and is on display inside a beehive kiln (a historic site) next to the Plainsman Clays plant. 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!