Glazing is quick and unforgiving. A pot that took an hour to throw is glazed in ten seconds, and almost every fault visible after the firing was created in those ten seconds: too thick, too thin, uneven, or on a surface that should have stayed bare.
Preparing the bisque
Bisque must be clean and dust free, because glaze will not stick evenly to a dusty or greasy surface. Wipe the pot with a damp sponge and let it dry, and handle it as little as possible afterwards: skin oils resist glaze and show as pale patches later. Wax the foot, or plan to wipe it, before anything is dipped.
Dipping, and getting the thickness right
Dipping gives the most even coat and takes the least time. The pot is submerged, held for two or three seconds and lifted out, and the porous bisque draws water in and leaves glaze behind. Thickness is controlled by the time and by how thick the glaze is in the bucket: too long or too thick and the glaze crawls or runs, too short and it fires dry and patchy. A test tile dipped once and twice shows the range.
Brushing, and when it is the right choice
Brushing suits decoration, small quantities and pots too big for the bucket. It needs a glaze formulated for it, three coats at right angles to each other, and each coat allowed to lose its shine before the next. It is slower and less even than dipping, and it is the only practical route for anyone glazing occasionally rather than in batches.
The faults, and what each one means
Crawling is glaze pulling away from the surface, usually because it went on too thick or over dust. Pinholing is gas escaping through the glaze late in the firing, often from an underfired bisque. Crazing is a fit problem between glaze and body rather than a glazing mistake. Running is too much glaze or too much heat, and it takes the kiln shelf with it, which is why the bottom centimetre of every pot stays bare.
Questions people ask about glazing pottery
How thick should glaze be?
About the thickness of a postcard on the fired pot, which usually means two to three seconds in the bucket. A test tile dipped once and twice shows what your glaze needs.
Why did my glaze crawl?
Glaze applied too thickly, or applied over dust or grease. Both stop the glaze wetting the surface properly as it melts.
Do I have to wax the foot?
You have to keep glaze off it somehow. Wax is the tidy way; wiping the foot clean with a damp sponge before firing works just as well.