Reduction vs Oxidation: Where Glaze Colour Actually Comes From

Two identical pots, glazed from the same bucket, can come out of two different kilns looking nothing alike. The reason is atmosphere — specifically, how much oxygen was in the kiln while the glaze was melting.

In an oxidation firing (what every electric kiln does), there’s plenty of oxygen. Metal oxides in the glaze stay fully oxidised, and you get predictable, stable colours — a copper glaze fires green, iron fires honey-brown to amber.

In a reduction firing (a gas or wood kiln, starved of oxygen at the right moment), the hungry flames start pulling oxygen out of the glaze itself. That same copper glaze, robbed of oxygen, fires a deep blood-red instead of green — this is where oxblood comes from. Iron shifts toward the cool grey-greens of celadon. Reduction is less predictable and harder to control, which is exactly why reduction glazes have a depth and variability that electric-fired ones rarely match. Our oxblood and celadon are reduction-fired; the honey and cobalt are oxidation. Same studio, two different fires.