The anagama is the oldest kiln form still in active use in Japan. A single, tunnel-shaped chamber dug into a hillside or built from refractory brick, fired with wood over two to four days. Granite Crest Zone fires its anagama twice a year, in spring and autumn. Students who have not fired in a wood kiln before often ask what the point is, given that an electric kiln is more controllable and more predictable. This article answers that question honestly.
The structure of an anagama ¶
An anagama is a single chamber, typically 2-5 metres long, with a firebox at the front and a flue at the back. The Granite Crest Zone anagama is 3.2 metres long and was built in 2017 using refractory brick from a supplier in Tokoname. The chamber slopes slightly upward from the firebox to the flue, which creates a natural draft that draws the flame through the kiln. Pieces are loaded throughout the length of the chamber, from the hottest zone near the firebox to the cooler zone near the flue. The position of a piece in the kiln determines what the fire does to it.
What the fire does to the clay ¶
In a wood-fire kiln, the flame itself touches the clay. This is fundamentally different from an electric kiln, where the heat is radiant and even. In the anagama, the flame path creates variation: pieces in the direct flame path get heavier ash deposit and more dramatic carbon flashing, while pieces in sheltered positions get subtler effects. The ash from the burning wood lands on the clay surfaces and, at temperatures above approximately 1,250°C, begins to melt into a natural glaze. This ash glaze is unpredictable in the best way. Its colour and texture depend on the wood species, the firing atmosphere, the position in the kiln, and the clay body.
Reduction atmosphere and what it means ¶
An anagama is fired in reduction. A condition where there is not enough oxygen in the kiln to fully combust the wood. This oxygen-poor atmosphere affects the chemistry of glazes and clay bodies. Iron-bearing clays and glazes shift toward warm browns, oranges, and greens in reduction, rather than the cooler, more oxidised tones you get in an electric kiln. The Shigaraki clay we use has enough iron in it to show clear reduction effects: the unglazed surfaces turn a warm orange-red, and the feldspar inclusions flash green or silver.
The stoking schedule ¶
The Granite Crest Zone autumn firing runs for approximately 60-65 hours. The first 20 hours are a slow climb to 900°C, during which the kiln is stoked every 20-30 minutes with small pieces of pine. From 900°C to 1,200°C the stoking becomes more intensive. Larger pieces of oak, every 10-15 minutes, with the damper adjusted to maintain reduction. The final push to 1,280°C is the most demanding: the stoker needs to read the colour of the flame at the flue and the behaviour of the draw tiles to judge when to push harder and when to hold. Students in the intensive take two-hour stoking shifts through the night.
Unloading and what to expect ¶
The kiln is sealed after the final stoke and left to cool for at least 48 hours before unloading. The unloading is the moment everyone has been waiting for, and it is always a mix of elation and disappointment. Some pieces come out better than anything you imagined. Some crack at the foot ring. Some are fused to the kiln shelf by a drip of ash glaze and have to be carefully chiselled free. Haruki keeps a loading diagram for every firing so that each piece can be traced back to its position in the kiln. This is how you learn, firing by firing.
The anagama is not efficient, not controllable, and not cheap to fire. It is also the most direct conversation between the maker, the material, and the fire that ceramics offers. That is why we fire it twice a year and why the places in the intensive fill quickly.