Urushi and Light

June 10, 2009

I was looking around on google scholar doing some searches about urushi in scholarly journals and I came across a study of the effects of light on urushi and I thought it would be a good thing to relay the knowledge.

Essentially, it is not recommended to leave urushi objects exposed to, not just UV light, but visible light for extended periods of time, if one wants to maintain the color and glossiness of the urushi surface. However, exposure to visible and minor amounts of UV light does not seem to have any significant effect on the mechanical properties such as hardness.

This was not a test of whether urushi is effected by Ultraviolet light, as it has been proven that urushi is significantly degraded by exposure to large amounts of ultraviolet radiation, but was a test of whether exposure to visible light effects urushi. The study was done to determine the effects of constant light exposure on urushi for display purposes in museums.

The study tested several properties and their changes through exposure to fluorescent light. The control was urushi that was kept unexposed to all light, and the variables were exposure to direct light (fluorescent tube, with UV peaks around 310 and 370nm, and peaks in the visible spectrum at around 400, 430, 500, 550 and 580nm), exposure through glass and exposure through acrylic. (each of these block slightly differing ranges of invisible light, and both block nearly all UV light with a wavelength shorter than 400nm) The exposure time was up to 5000 continuous hours.

The visual properties tested were, color and relative gloss. The mechanical properties tested were, hardness, tensile strength and the elastic modulus.

The results indicate that the properties change over time and exposure in this manner:

Color: There is a 3-5% color change with the greatest change in the direct exposure and the smallest change with exposure through glass. The control had no change.

Relative Gloss: There was a significant reduction in relative gloss of up to 10 percent over the full exposure period and there was no significant difference between direct exposure, exposure through glass, and exposure through acrylic. The control had no change.

Hardness: There was no significant difference between the control and variables, and the hardness in all samples increased over time.

Tensile Strength: There was no significant difference between the control and variables, and the tensile strength in all samples decreased over time.

Elastic Modulus: There was no significant difference between the control and variables, and the elastic modulus in all samples increased over time.

The conclusion was that urushi lacquer is effected by visible light as well as ultraviolet light in its color and gloss, however its physical properties are not effected by the presence of visible and minor amounts of ultraviolet light.

Citation:

Toshio Ogawa, Kazutaka Arai, Satoshi Osawa.

"Light Stability of Oriental Lacquer Films Irradiated by a Fluorescent Lamp."

Journal of Polymers and the Environment

http://www.springerlink.com/content/n702360v8774m06x/

Ern.

Edited June 11, 2009 by SJM1123