Composition changes of water extracts from Asian lacquer surfaces during artificial aging and the influence of formulations

• Published in: Journal of cultural heritage Vol. 66; pp. 602 - 612
• Main Authors: Han, Jing, Schilling, Michael R., Mazurek, Joy, Webb, Marianne, Hao, Xinying, Khanjian, Herant
• Format: Journal Article
• Language: English
• Published: Elsevier Masson SAS 01.03.2024
• Subjects: Additive impacts; Asian lacquer; Gas chromatography–mass spectrometry (GC–MS); Light aging; pH values; Water-soluble products; Water-soluble products; Additive impacts; pH values; Asian lacquer; Gas chromatography–mass spectrometry (GC–MS); Light aging
• ISSN: 1296-2074; 1778-3674
• DOI: 10.1016/j.culher.2024.01.012

•An analytical protocol was developed to study water extracts from aged lacquer.•12 New compounds were identified as aging products of lacquer.•During aging, pH, conductivity, and peak areas and indices of components changed.•Iron treatment caused the most changes in water extract while drying oil the least. Lacquered artifacts are among the most exquisite objects in museum collections. However, during aging, a considerable quantity of water-soluble products are formed on the lacquered surfaces, posing significant conservation and preservation challenges. This paper presents in-depth research on the composition of these water-soluble products by the investigation into water extracts from Asian lacquer coatings during artificial aging. Lacquer coatings of 15 specially designed formulations involving different lacquer tree saps (urushi, laccol, and thitsi), drying oils, tree resins and pigments were produced and artificially aged. A set of analytical methods was developed including pH and conductivity measurements, and peak area and index analyses based on gas chromatography–mass spectrometry (GC–MS). Results show that artificial light aging cause the formation of a complex array of hydroxyl carboxyl benzenes (Webboxy products), while simultaneously decreasing the amounts of saturated straight-chain dicarboxylic fatty acids and glycerol. Distinct changes in the average number of hydroxyls and carboxyls bonded to the benzene rings or average chain length of the dicarboxylic fatty acids have also been observed with light aging. The additive that impeded light degradation and formation of water-soluble products the most is drying oil, and the additives that accelerated composition changes of water-soluble products was iron (treatment). Additionally, 12 new compounds have been identified as aging products of lacquer, such as tetramethyl dimethoxybenzene tetracarboxylate and benzene hexacarboxylic acid hexamethyl ester. The understanding of pH and conductivity readings of water extracts from aged lacquer is significantly improved. The research results contribute to the knowledge of aging pathways and mechanisms of alteration to Asian lacquer coatings. [Display omitted]