The Process, Continued - Glazing
Glazing is the process of covering a pot with a coating of fine-ground minerals that is fused to the surface of the pot by firing it.
Any particular glaze is created out of 3 to10 or more ingredients from a selection of thousands of wondrous materials with names like kaolin, nephtheline syenite, and cobalt carbonate. These ingredients fall into four categories: 1) Silica, which is the base material for glass and for ceramic glazes, and a major component of raw clay; 2) Fluxes, which lower the melting point of the silica, without which it couldn't be used to make glazes; 3) Alumina, or aluminum oxide, which allows the glaze to stick to a pot's vertical surface without running when it melts; and 4) Colorants and Glaze modifiers which produce a wide range of colors and effects.
Glazes are formulated to melt at specific temperatures and to yield a matte or glossy finish.
There are hundreds of thousands, if not millions, of glaze recipes with very specific combinations of these ingredients, generally.
There are many reasons to glaze a pot. Glaze can make the pot non-porous so that liquids can be stored indefinitely. Glaze can also make the pot stronger. And, of course, glaze can make the pot beautiful.