Wood & Substrate Prep

Urushi has been applied to almost anything — bamboo, woven fabric, paper, leather, ceramics, even metal armor plate — but wood remains the classic substrate, and the choice of species is not incidental. Conservation literature on Japanese lacquer identifies the common historical substrates as hinoki (Japanese cypress), elm, and quince, with fabric, paper, leather, and ceramic used for smaller or specialty objects. (Conservation Wiki, Lacquer) Wajima-nuri, one of Japan's most prestigious lacquerware traditions, is built specifically on "delicate zelkova [keyaki] wooden substrates" — a dense, fine-grained hardwood chosen for its dimensional stability under the repeated wetting/humidity cycles that urushi curing demands. (Wikipedia, Wajima-nuri)

Kiji-gatame: stabilizing the wood before any coat goes on

Before the first ground layer, the raw wooden object (kiji) goes through kiji-gatame — "wood hardening/fixing." Any imperfections, knots, or small gaps are filled with kokuso (raw lacquer, rice glue, and zelkova wood meal — full recipe in Chapter 13), and then the whole piece is saturated with a thin coat of raw lacquer specifically to stabilize the wood and reduce warping as it moves through repeated humid curing cycles. The surface is then polished — traditionally with sharkskin boards, or sandpaper for a modern equivalent — to key the surface for the ground layers that follow. (Japan Artisan Foundation, Shitaji-nuri)