firing, cones, and what 1280 degrees means

Everything before the kiln is proposal; firing is the decision. Clay goes in as compressed dust held together by hope and comes out as stone. Understanding what happens in there, and what the mysterious cone numbers mean, is what turns firing from a lottery into a craft.

two firings, not one

Almost all pottery is fired twice. The bisque firing (slow, to about cone 06, around 1000 C) drives off water and burns out organics, leaving the pot hard but porous, ready to absorb glaze. The glaze firing then takes the work to its clay body's maturing temperature, where the body vitrifies and the glaze melts to glass. Single-firing exists and is a discipline of its own; learn the two-step first.

cones: temperature with a memory

A pyrometric cone is a small pyramid of glaze-like material engineered to bend at a precise amount of absorbed heat. Not just temperature: heat over time, which is what clay and glaze actually experience. A fast firing to 1280 C does less work than a slow one to the same number, and cones measure the difference. When a cone 10 cone bows over, cone 10's work is done, whatever the pyrometer claims. It is the same reason our preloader counts to 1280 and says 'cone 10': that is this studio's endpoint.

oxidation and reduction

An electric kiln fires in oxidation: plenty of oxygen, clean and predictable, colours bright and even. A gas or wood kiln can be starved of air into reduction: the flame, hunting for oxygen, pulls it out of the metal oxides in clay and glaze. Copper turns from green to blood red, iron speckle blooms through the glaze, celadons go sea-grey. Same materials, different chemistry, and the reason two potters with identical recipes make unrecognisably different work.

wood firing, the long way round

A wood firing runs one to three days of continuous stoking. Ash rides the flame through the chamber and melts onto the work as natural glaze; flame paths shadow and blush the clay where pots shield each other. No two shelf positions receive the same fire, which is why wood-fired pieces cannot be repeated, only made again differently. It is the logic this studio's whole catalogue is built on, and the reason the maker opens the kiln door with no idea what she will find.

the parts nobody romanticises

• Ramps matter: water and carbon must leave slowly below 600 C or the work spalls. Kiln programs exist for a reason.
• Quartz inversion at 573 C: the silica in clay physically snaps size in both directions. Fast cooling through it cracks pots that survived everything else (dunting).
• Never open a kiln above about 150 C, however strong the temptation. Patience is a firing tool.
• Kiln attrition is real: expect to lose the occasional piece to warps, cracks, and glaze accidents forever. Around one in ten early on is normal, not failure.