Japanese urushi and traditional Asian lacquer

Overview

Urushi is the Japanese word for the sap of the Chinese lacquer tree (Toxicodendron vernicifluum) and, in English, a collective term for Asian lacquerware made from the sap of this and related species. Wikipedia says the sap contains urushiol, an allergenic irritant; it is the same family of oil found in poison ivy and poison oak. The sap is tapped from the trunk, then filtered, heat-treated or coloured before being applied. Wikipedia says curing needs a warm, humid chamber for 12 to 24 hours, during which the urushiol polymerizes into a clear, hard, waterproof surface. This is not the nitrocellulose or shellac lacquer used in modern workshops; those are described in Nitrocellulose lacquer and Shellac.

Pros

• Wikipedia describes the cured film as clear, hard and waterproof.
• A long tradition of fine craft work, built up layer by layer.
• Takes pigment; Wikipedia mentions red (iron oxide) and black (magnetite) traditional colours.

Cons

• Wikipedia says that in its liquid state urushiol can cause extreme rashes, even from vapours; once hardened, reactions are possible but less common (the article marks that second point as needing a citation).
• Cures only in humid, warm conditions, not by simple air drying.
• Slow, skilled work; repairs are hard.
• Expensive and hard to source; no manufacturer product pages were verified for this entry.

Suitability

A craft finish for small, high-value objects such as bowls, trays, boxes and decorative furniture. It is not a practical production finish for a general shop; an experienced lacquer craftsperson or supplier should be consulted. The listed woods are examples: Hard maple and European beech are close-grained and stable.

Coats and application

Wikipedia says lacquer is painted on with a brush and cured in a warm, humid environment. Craft practice involves many thin layers, each cured and then abraded; the source opened for this entry does not give schedules or humidity values, so do not treat the figures here as instructions. Learn from a trained practitioner before attempting it.

Compatibility

Urushi is a self-contained system; it is not intended to be mixed with modern varnishes or oil finishes. Test any pairing on a sample; the sources opened do not cover compatibility.

Care and repair

The source opened for this entry gives no care instructions; ask the supplier or maker. Repair is a specialist job.

Safety and environment

Treat uncured urushi as a skin sensitizer. Wikipedia says that in its liquid state urushiol can cause extreme rashes, even from vapours. Wear nitrile gloves, cover skin and ventilate; know the symptoms of poison-ivy dermatitis and keep first-aid information to hand. Those allergic to poison ivy or poison oak should not work with it. Cured work is described as less likely to cause a reaction but not risk-free.

Related

• Shellac: the other natural film finish.
• Nitrocellulose lacquer: the modern lacquer.
• Beeswax and carnauba: simple natural waxes.
• Hardwax oil: a modern natural-oil approach.
• Food-safe finishes: how to read claims.