BlogArgilla's first posts are about my research into making an Egyptian paste, which is a self-glazing compound. Amy Waller's site is a very good primer on the subject, and has some great links. Egyptian paste is not suitable for food; it is weak, porous, and is used for making symbolic and decorative objects.
The first question might be, why bother with combining glaze and clay into one compound? The short answer is that it bypasses the potter's Sisyphean routine of firing everything twice. As if once wasn't enough. This opens opportunities to produce work in small spaces, without the investment of a large kiln. It allows the making to be less technical, and therefore more people can avail themselves of it. It also lays the ground for the possibility of developing a slip-glaze, i.e. a compound that applies like a slip, and fires like a glaze, great for sgraffito.
Sometimes Egyptian paste is called Egyptian Faience; let's not get stuck on colonialist labels for now. What we are talking about here is a composed paste/clay with a fair range of variations in its ingredients and in their composition, and none of them have anything to do with Faience. The earth in the region of the Levant and other nearby areas is very highly saline. For example, in the Red Sea, the saltiest body of water on earth, one is buoyed on the surface, never sinking, there is so much salt in the water. Salt is a flux, and if there is enough of it in a paste or clay body it will effloresce, i.e. migrate, to the surface as the paste dries. When fired, this migrated salt can help form a glassy surface.
I will return to the subject of efflorescence, because it is a key mechanism of this self-glazing paste. Efflorescence, from the French effleurer, or to flower, is an aptly descriptive term. We shall look at how to encourage the flowering of salt with its pros and cons.
It's salt! Uncommon efflorescence of salt in the local metro station. A pinch of barium carbonate is used in the brick industry to inhibit this kind of thing.