A preliminary examination of urushi-based conservation options for the treatment of photodegraded Japanese lacquer using scanning electron microscopy and profilometry

Urushi is the Japanese term for the sap of the lacquer tree Toxicodendron vernicifluum, a natural crosslinking polymer that has been used for thousands of years as a durable decorative coating. Photodegradation combined with fluctuations in relative humidity cause the formation of microcracks that lead to a reduction in gloss and eventual loss of the surface. In Japan, historic lacquer objects are often conserved with urushi-based methods called urushi-gatame and suri urushi. This paper compares the potential effectiveness of these treatments for enhancing the long-term preservation of historic photodegraded Japanese lacquer surfaces. Images of naturally aged lacquer samples were made with a scanning electron microscope (SEM) before they were treated using urushi-gatame and suri urushi. Samples were then artificially aged, imaged with the SEM, and assessed using a vertical scanning interferometry profilometer. The results indicated that urushi-based treatments may be problematic for export- type lacquers with a proteinaceous ground. While further work is required, this preliminary study suggests that, excluding the formation of new microcracking, three dilute urushi applications may represent the minimum urushi-based treatment required to enhance the long-term preservation of a photodegraded lacquer surface significantly