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

Abstract

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.