The Nature of Urushi

The quality of urushi varies according to the location, time of year and method by which it is taken.
Urushi taken from the tree in an unrefined state is called arami and after it has been strained it is then called ki-urushi.
It can of course be used in an unrefined state for processes such as undercoating but when it dries it becomes a brownish color so for top coats the urushi needs to be refined and processed.
This process is called kurome or nayashi.
By heating ki-urushi the water content is reduced. It is adjusted in this way to make it more viscous so that it is easier to apply and to produce a luster when it dries.
As a result of this process the properties of urushi also change.
From the time that the urushi is taken from the tree to refinement the seasoned techniques of the craftsman are brought to life in the urushi itself.

The Time of Urushi

The main constituent of urushi is urushiol.
Urushi differs from other paints and varnishes which dry as a result of the volatization of solvents in that urushi dries as a result of the oxidization of urushiol which is due to an enzymatic reaction that occurs when urushi comes into contact with air.
For this process a specific range of temperature and humidity is necessary as if one or both of these is either too high or too low various problems will be encountered in the drying process.
In fact, even after this reaction has taken place subsequent drying continues gradually.
Therefore, when Wajima-nuri is first used please take as much care as possible with its handling.
One year after completion it can be handled normally and after three years of use a deep luster forms and the piece can at last be considered complete.
When urushi has completely hardened it is not affected by acids or alkalis and can last for thousands of years.
Some remains have in fact been excavated of urushi utensils that date back about 6000 years to the Jomon period and although the wooden substrate has decayed, the original coating of urushi has survived retaining its original color and luster.


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