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49

Science of lacquer

Lacquer has been used not only in Japan but also in the countries of Asia since the ancient time applying it to daily-used tools. When dried, lacquer is resistant to acid, alkali, saline (salt), alcohol, etc. But whey does lacquer has such characteristics? Here, lacquer will be described scientifically.
Difference in primary component according to the country where the lacquer was collected
The primary component differs according to the country where the lacquer was collected. In the lacquer collected in Japan and China, its primary component is urushiol. In the lacquer collected in Vietnam, its primary component is laccol. In the lacquer collected in Myanmar, its primary component is thitsiol.
Difference in components included in raw lacquer according to the country where the lacquer was collected
Type of raw lacquer Moisture Primary component Nitrogen contained Gum material
Collected in Japan 25.1 67.3(Urushiol) 2.1 5.5
Collected in China 27.5 65.0(Urushiol) 2.2 5.3
Collected in Vietnam 32.5 52.5(Laccol) 2.0 13.0
Collected in Myanmar 26.8 69.5(Thitsiol) 2.5 1.7
In Japan, it is considered that the more urushiol is contained, the high quality the raw lacquer.
Although both the lacquer collected in Japan and the lacquer collected in China include urushiol, the lacquer collected in Japan include more urushiol.
What is Urushiol?
Urushiol is oil. Urushiol is in the state of water in oil type emulsion where moisture is contained in oil. Milk is a representative of oil in water type emulsion which is the opposite of urushiol. Urushiol is a compound formed of three components which are C (carbon), O (oxygen) and H (hydrogen).
How does lacquer become dry?
Drying process of lacquer is different from how paint dries due to the moisture therein evaporating. In lacquer, an enzyme called laccase is activated at adequate temperature (about 25 degrees) and humidity (about 85%), takes in oxygen from the moisture in the air and supplies oxygen to urushiol. In such way, urushiol is oxidized and hardens. This is referred to as oxidation polymerization. Lacquerware is put in a dryer called “bath” to be dried. In the “bath”, temperature and humidity inside are adjusted constantly so as to maintain the adequate temperature and humidity in which laccase can be activated.
High molecular coating film of lacquer
The coating film of lacquer is durable because it is a high molecular coating film including large number of molecules. In the liquid state, lacquer is in low molecular state and thus, lacquer can be handled with a brush. However, once it is hardened, the molecules are joined together in the form of mesh. This is why the coating film is durable.
On the other hand, lacquerware should not be placed and stored in sunlight because ultraviolet light destroys the high molecular state of the coating film.
Coating film of lacquer prevents damages due to aging
When urushiol is oxidized and hardened, the gum material forms a film that covers urushiol so as to prevent urushiol from being further oxidized. In such way, oxidization of the coating film of lacquer is minimized and the durable coating film can be maintained.