Urushi (Japanese Lacquer)

Urushi (漆) is the sap of the lacquer tree, Toxicodendron vernicifluum, tapped much like rubber or maple syrup and refined before use. Its active ingredient, urushiol, is a mixture of phenols that oxidizes and polymerizes under a naturally occurring enzyme, laccase, into an exceptionally hard, glossy, and chemically resistant coating once it cures.

That curing process is the part most people get backwards: urushi doesn’t dry out the way ordinary varnish does. It actually needs a warm, humid environment, typically kept in a controlled cabinet called a muro, to absorb enough moisture and oxygen for the enzyme reaction to finish. A dry room will leave it tacky indefinitely.

Raw, uncured urushiol is also the reason lacquer artisans handle the sap with real caution. It’s the same class of compound found in poison ivy and poison oak, and contact with wet urushi can cause a severe skin reaction in people who aren’t already sensitized. Once fully cured, though, the surface is chemically inert and safe to eat and drink from, which is exactly why it’s been used on tableware in Japan for thousands of years, including lacquerware found at the Kakinoshima site in Hokkaido dated to roughly 9,000 years ago, among the oldest known lacquerware anywhere in the world.