glazing basics: the chemistry coat
l.09 · 8 minute read · updated July 2026 · by the studio
Glaze is glass, ground up and suspended in water, painted onto a pot and melted back into glass in the kiln. It is the step where months of throwing practice meets chemistry, and where more finished work is ruined than anywhere else in the craft. It is also where the magic lives: the same bucket of dull grey liquid becomes a night sky or a sea green depending on ten degrees and a whim of the flame.
what is in the bucket
Every glaze is three jobs in one recipe: silica forms the glass, alumina stiffens it so it does not slide off the pot, and flux persuades it all to melt at your kiln's temperature. Colour comes from metal oxides in small percentages: iron for ambers and tenmokus, cobalt for blues, copper for greens, titanium and rutile for speckle and break. Our six studio glazes are all variations on this arithmetic; the glossary covers the terms one by one.
before any glaze touches the pot
- The pot must be bisque fired (a first, lower firing around cone 06) so it is hard enough to handle and porous enough to drink glaze.
- Wipe or rinse off every trace of dust; dust is the number one cause of crawling.
- Wax the foot ring and 3 mm above it with wax resist. Glaze that touches the shelf becomes a permanent bond, and shelf-grinding is nobody's hobby.
- Stir the bucket until it is single cream, top to bottom. Glaze materials settle hard; ten seconds of stirring is never enough.
dipping and brushing
Dipping is the studio standard: grip the pot with tongs or fingers, one smooth plunge, three seconds, one smooth exit, shake off the drips and do not touch it while wet. It leaves an even coat about as thick as a credit card. Brushing suits small work and decoration: three thin coats in alternating directions, drying between. Brush-on bottled glazes (the kind sold for home use) are formulated thicker for exactly this.
the five defects everyone meets
| defect | what you see | usual cause |
|---|---|---|
| crawling | bare islands where glaze retreated | dust or oil under the coat, or too thick |
| pinholing | tiny craters like orange peel | gases escaping late; often bisque too cool or firing too fast |
| running | glaze pooled at the foot or welded to the shelf | too thick, too fluid a recipe, kiln overfired |
| crazing | fine crackle network in the glaze | glaze shrinks more than clay; a fit mismatch |
| shivering | glaze flakes off edges in slivers | the opposite mismatch, and the dangerous one; retire the piece |
Crazing on decorative work is often kept deliberately (the crackle on our moon jar is exactly this, controlled). On food surfaces it is a hygiene question, which food safe ceramics treats properly. Shivering is never acceptable anywhere; it puts glass slivers in food.
test tiles or gambling
Every serious potter keeps a library of fired test tiles: this glaze, on this clay, at this cone, thin and thick, alone and layered. It feels like homework and it is the only alternative to gambling months of work on a guess. Fire tiles in every load; the kiln always has corners going spare. What the kiln then does to your careful chemistry is the subject of firing and cones.
common questions
can you glaze pottery without a kiln?
No. True glaze must melt at 1000 C or more. Paints and sealants sold as cold glaze are coatings, not ceramic glaze, and are not food safe or dishwasher proof.
why did my glaze come out rough and dry?
Usually applied too thin, or the kiln underfired. Check thickness with the scratch test before firing and confirm your glaze's cone matches the firing.
do you glaze the bottom of pottery?
The foot ring is left bare or waxed so the piece does not fuse to the kiln shelf. Some potters glaze inside the foot ring but never the surface that touches the shelf.