The Art of Yakisugi

Yakisugi is a Japanese method of preserving timber by charring it. The name is literal: yaki is to burn, sugi is Japanese cedar. Boards were charred on one face, cooled, brushed back and oiled, then used as exterior cladding - where the burnt layer resisted rot, insects and, counterintuitively, fire.

You may know it as shou sugi ban. That's the same three characters read a different way, and it stuck in the West even though it isn't what the technique is called in Japan.

Why walnut is not sugi

Traditional yakisugi works on cedar for a reason. Sugi is a softwood with a pronounced difference between its soft spring growth and its harder summer growth. Char it and the soft bands burn away faster, so brushing back leaves a rippled, alligator-skin texture - the grain standing physically proud of the surface.

American walnut doesn't do that. It's a hardwood with an even, diffuse pore structure, so the char sits more uniformly and the surface stays flatter. What you get instead is depth: a black that isn't paint, sitting over a timber that was already dark, with the figure still legible underneath.

Three passes

The char is done with a gas torch, and not aggressively. Three passes, and between each one the loose char is brushed off with a carbon bristle brush, back to sound timber, then burnt again.

The reason for working in passes rather than one long burn is control. A single heavy pass gets you black quickly, but it's a soft, powdery black that keeps shedding, and on a hardwood it will scorch unevenly wherever the torch lingers. Building it up in layers means each pass only has to darken what's already there. You stop when the surface is fully black and the brush stops lifting anything off it.

The shape

The board isn't a rectangle with a handle stuck on it. The face is an elongated hexagon, drawn out to a point at one end, and the handle runs off the other through a waisted neck rather than a shoulder - so the outline is one continuous line from tip to grip.

It costs more to make this way. Every one of those angles is a facet that has to be cut, faired and eased by hand, and there are far more of them than a rectangle asks for.

The brass

Six-millimetre brass, inlaid into the face.

There are two pieces of it, and neither is decoration for its own sake.

The first is a ring, set into the hanging hole at the end of the handle. It's the point on any board that takes the most wear - a hole in end-heavy short grain, rubbing against a hook or a peg every time the board goes up or comes down. Lining it in brass puts metal where the wear happens.

The second is a single bar, inlaid across the point at the opposite end. Stand the board upright and that's what it rests on: the sharpest, most vulnerable corner of the piece, shod in brass.

Two small pieces, both of them at the places a board gets damaged.

The channels were cut with a plunge router running against a jig, and the brass set in with epoxy - all of it before the board ever saw the torch.

That order is the part worth explaining. Inlaying into an already-charred surface means cutting through the char at every edge, and the char is fragile: it chips at the margin and leaves a grey, broken line around the metal. Doing it the other way round, the brass is already home when the flame arrives, and the burn closes over the joint instead of opening it. The brass takes the heat and comes back to gold under the brush.

Brass was the right metal for this rather than steel or copper: it stays warm against black, and it takes a polish that reads as deliberate. It will also tarnish over time, which is worth saying plainly. Acidic food - lemon, vinegar, anything cured - will speed that up. Left alone it dulls to a softer gold. Polished occasionally, it comes back.

The finish

Rubio Monocoat Oil Plus 2C. One coat, no film: the oil bonds to the timber fibre rather than sitting on top of it, which matters on a charred surface where a film finish would sit over the texture and flatten it. It's food-safe once cured, and repairable in place - a scratch can be spot-oiled rather than requiring the whole board to be stripped.

580 × 360 × 30 mm.

Living with it

The char is brushed back and sealed. It doesn't come off on food, and it doesn't rub off on hands.

Rubio bonds at a molecular level rather than sitting on the surface, so there's no schedule to keep and no annual re-coat. If the board is used often and starts to look dry, a wipe of mineral oil brings it back.