Surface metrology concepts and practice applied to modern asian lacquer surfaces made with laccol, thitsiol and urushiol

Patrick Ravines, Marianne Webb, H. David Sheets, Herant Khanjian
Patricia H. and Richard E. Garman Art Conservation Department, Buffalo State College
Getty Conservation Institute (GCI), Los Angeles, USA

Research at the Getty Conservation Institute on the characterization of Asian lacquer has demonstrated that the type of lacquer and the additives can have an impact on the behaviour of the resulting surface. As part of the GCI’s ongoing project to understand the aging characteristics and develop cleaning methods for Asian lacquers, Conservator Marianne Webb, prepared 15 different formulas of Asian lacquer using laccol, thitsiol and urushiol with the most common additives: oils, pigments and resins. The five formulas within each of the three lacquer categories differ from the next in the series by one ingredient. This approach allows us to understand how each ingredient affects the nature of the surface texture. Observation, examination and analysis of the surface at each stage of the experiment ranging from freshly made to aged to cleaned lacquer surfaces is key to following the changes over time. The Asian lacquer panels, prepared in 2017, strictly followed recipes and preparation protocols to minimize differences and ensure standardization of the final products.

Surface metrology and multi-scale analysis using confocal microscopy will be introduced and discussed in relation to the 15 Asian lacquer panels investigated. 12 distinct areas of interest using 10x (area 1,600×1,600 μm) and 50x (320×320 μm) objectives were examined on each lacquer panel. Each area examined yields unique areal surface texture measurements. The analysis of areal surface texture measurements yield descriptive surface texture parameters that comply with ISO standard 25178. There are several groups of surface parameters and the two used in this study are height and spatial parameters. All height parameters and a few parameters from the spatial group have been selected and used to describe the surface texture of the 15 panels. The height parameters describe the mean height of the surface (root mean square height (Sq) and arithmetic mean height(Sa)), skewness (Ssk), kurtosis (Sku), maximum peak height (Sp), maximum pit depth, i.e. the lowest point of the surface (Sv), and Sz as the maximum height of the surface, i.e. is sum of the absolute values of Sp and Sv parameters. The parameter from the spatial group used is texture direction (Std). Other parameters used are the number of peaks and number of pits of the region of interest.

We look forward to presenting this new quantitative approach to the study of Asian lacquer surfaces and starting a discussion on surface texture features that are of interest.