Tanso Editions



Two special edition pieces exploring alternative wood treatments for outdoor furniture.

Wood is inherently a biodegradable and dimensionally unstable material. These characteristics present problems such as rotting and warping, issues which become increasingly challenging to manage when designing for outdoor environments. The Tanso Editions have been designed in a bid to overcome these challenges through the application of two different timber treatments. The oak bench has been finished using the ancient Japanese technique of charring wood, ‘Shou-Sugi-Ban’, and the chair is made from beech that has been thermally modified by heating it in an oxygen-free environment. Both treatments improve the timber’s climatic resistance and dimensional stability to the highest ‘Class 1’ durability*.

*Timber Durability is measured in 5 classes under the EN350 classification system, with each class determining how long each timber will survive outdoors. These range from class 1 – very durable, lasting 25+ years, to class 5 – perishable, lasting less than five years.

The Japanese practice of ‘Shou-Sugi-Ban’ dates back to the 1700s. Traditionally, Sugi (Japanese cedar) was used. However, the same results can be achieved in most open-cell species. The process involves charring the wood, cooling it, cleaning it, and finishing it with natural oil. It works by applying fire to the wood’s surface for a short period. This burns off the softer, cellulose parts of the timber, leaving the harder areas of lignin behind. The remaining charred layer of lignin protects the wood from UV and weathering and is much more fire-resistant (the more combustible cellulose having been removed). Carbonising removes nutrients and sugars commonly eaten by insects and rot-producing fungi. Timber treated in this way can last more than 80 years.

MATERIALS: Solid Oak and Thermally Modified Beech

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As seen in the process of Shou Sugi Ban, altering wood’s properties by using heat has been practised for many years. However, the commercial thermal modification of timber (TMT) is a relatively recent development.

TMT originated as a way to improve the performance and durability of softwoods but has since extended into hardwoods, allowing new kinds of timber to be used outdoors. Unlike most other treatment processes, the thermal modification process involves no chemicals and reaches the core of the wood rather than merely treating the surface. By heating timber to a temperature between 180-240 ºC, the moisture content is reduced to less than 5%, and the cell structure is fixed, meaning it can no longer absorb moisture and is much more dimensionally stable. Sugars and resins are also cooked out of the wood, removing the carbohydrates that feed mould, fungus or bacteria.

The thermal modification process changes the wood's cellular structure and colour, producing an exotic appearance similar to tropical species such as teak. This process adds value to domestic woodlands, creating a market for under-utilised hardwoods like beech and providing an alternative to some less-sustainable tropical timbers.

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