Wood-firing is not simply an alternative fuel source — it is a fundamentally different process from gas or electric firing, one in which the kiln atmosphere, ash deposition, and flame path become active participants in surface creation. The results are unpredictable in the details and consistent only in character: warm, often matte surfaces with depth and variation that emerge from the specific conditions of a particular firing rather than from glaze chemistry alone.
The Anagama: Structure and Origin
The anagama (cave kiln in Japanese) is among the oldest kiln forms in the world, with documented use in Japan dating back to the fifth century. Its defining characteristic is a single elongated chamber built into or against a slope, with a firebox at the lower end and a chimney flue at the upper end. The slope is not decorative — it creates natural draft, drawing combustion gases from the firebox through the stacking chamber and out the flue without mechanical assistance.
In North American studio contexts, anagama kilns are typically brick-built structures capable of reaching cone 10–13 (1280–1380°C). The chamber length varies considerably: smaller educational kilns may be 2–3 metres long, while larger community kilns built for multi-day firings can exceed 6 metres. A longer chamber generally allows more variation in temperature and ash deposition across the stacking zone — a feature potters deliberately exploit by positioning pieces at different distances from the firebox.
The Noborigama: Chambered Efficiency
The noborigama (climbing kiln) replaced the single-chamber anagama in Japan during the late sixteenth century and spread rapidly through Korea and China as its efficiency advantages became clear. Rather than one elongated chamber, the noborigama consists of a series of connected chambers arranged in a rising row up a hillside. Each chamber is fired in sequence — heat and gases from the lower chamber pre-heat the next, reducing the total wood consumed compared to firing each chamber independently.
In Canadian studio practice, noborigama kilns are less common than anagama structures, partly due to the greater complexity of construction and partly because fewer studios have access to suitably sloped terrain. Notable exceptions include several pottery centres in British Columbia, where the combination of abundant firewood from managed forests and topographically varied terrain has made multi-chamber kilns more practical.
Wood as Kiln Atmosphere
The character of wood-fired surfaces comes primarily from two related phenomena: fly ash and flame effects. As wood burns, fine particles of ash are carried through the kiln by the draft. Some of this ash lands on the surfaces of pots in the stacking zone. At high temperatures, ash begins to flux — it behaves similarly to a high-flux glaze material, melting onto the pot's surface and creating a natural glaze effect that was not applied by the potter at all.
The chemistry of this natural ash glaze varies with the species of wood burned. Cedar ash produces softer, more translucent effects; oak ash tends toward thicker, more opaque deposits; pine produces more volatile and aggressive surfaces. Many wood-fire potters keep detailed notes on the wood species used in each firing, treating fuel selection as a deliberate material choice rather than simply a matter of availability.
Reduction — an atmosphere in which there is insufficient oxygen for complete combustion — affects both the clay body and any applied glaze. Iron-bearing clay bodies, the most common choice for wood firing, shift from warm buff tones in oxidation to grey, blue-grey, or near-black in heavy reduction. The same iron oxide that produces amber in oxidation fires to green celadon in reduction — a chemical transformation driven by atmospheric conditions rather than temperature alone.
Temperature Variation in the Anagama Chamber
Temperature variation within a single anagama firing is not a defect to be corrected — it is a feature to be managed. The area directly in front of the firebox, known as the "hot spot," may reach temperatures 100–150°C higher than the back of the chamber. Experienced potters use this gradient deliberately, placing heavily grogged pieces that can withstand thermal shock in the hot zone and more delicate work further back.
Organising a Community Wood Firing
A single anagama firing typically consumes 1.5–4 cubic metres of split hardwood over 24–72 hours. This quantity of fuel, the physical labour of stoking every 15–30 minutes through the night, and the risk of a failed firing that affects dozens of pieces — all point toward collective rather than individual operation. Community firings are a defining feature of the wood-fire tradition in Canada, with participants sharing both the loading, the stoking shifts, and the unloading work.
The loading of a kiln for wood firing requires more planning than gas or electric loading. Pieces must be elevated off the kiln shelf on wads of alumina-silica mix to prevent ash glaze from bonding the pot to the shelf. Spacing is critical — air and flame must be able to circulate between pieces for even ash deposition. Tall pieces are typically placed toward the front where draft is strongest; smaller, closed forms do better mid-kiln where ash accumulation is more moderate.
Reading a Wood-Fire Result
Unloading a wood-fired kiln — a process called "the reveal" by some practitioners — is different in character from unloading gas or electric work because the outcome of individual pieces was genuinely uncertain at the time of loading. A piece placed 60 centimetres from the firebox will have a dramatically different surface than the same piece placed 2 metres back, even if both were covered in the same applied slip before loading.
Understanding a wood-fire result requires reading the ash deposit direction (which reveals flame path), the glaze colour shift (which indicates atmosphere at that location in the kiln), and any flash markings from nearby shelves or pieces. These marks are evidence of the kiln's specific behaviour during that specific firing — a record that cannot be reproduced exactly, even if all variables are held constant.
The Wood Fire Canada network documents active anagama and noborigama kilns across Canadian provinces, including firing schedules and open-community loading invitations.
