Urushi is a kind of natural lacquer collected from the Urushi tree. We Japanese have a 6000 year history of the use of Urushi.
Initially it was used as an adhesive, like fixing an arrowhead to the wooden shaft, applying gold foil or fixing chipped porcelain. Then it came to be used for finishing lacquer soup bowls and furniture.
The Urushi tree grows in many parts of east Asia including Japan. Collecting Urushi is like collecting gum from rubber tree. We cut the bark of the tree and then the tree yeilds a milky-white sap to cure the wound. Because this is a very labor intensive process we produce only a little amount of Urushi in Japan nowadays. We commonly use Chinese Urushi.
Urushi is very resistant to acid, alkali and alcohol. Furthermore, it withstands almost 300 degrees centigrade(600 degrees Fahrenheit) heat. Its only defect is its vulnerability to ultraviolet rays like other natural finishes.
I use raw Urushi as the finishing lacquer on my works. The process is something like oil finishing. We spread Urushi on the surface of the wood and wipe off the excess. Then we dry and sand-paper it, and we repeat this process several times.
Unlike oil fhinishing, it requires heat and humidity to dry Urushi, because the ingredient of Urushi must be oxidized and polymerized to be hardened. It is hardened in 75%-90% humidity and a temperature of more than 15 degrees centigrade. So in old times we could not do Urushi finishing in winter. The best time for Urushi-work had been the rainy season and rainy day in summer. But in these mordern days we can prepare a specially air-conditioned room and do the work anytime throughout the year.
One of the difficult parts of handling Urushi is most people are allergic to it, but happily I am not one of them. But one can overcome the allergy if one is patient and has the courage to continue the work. Once Urushi is completely dried, no one has an allergic reaction to it.