Zinc oxide-centred deterioration in 20th century Vietnamese paintings by Nguyễ Trọng Kiệm (1933–1991)

Five paintings dated 1963–1980, by Vietnamese artist Nguyễn Trọng Kiệm (1933–1919) in the Witness Collection, are investigated through study of paint cross–sections. Zinc oxide predominates in all paintings, and has strongly influenced their ageing. Widespread flaking is an ongoing concern. Unusual zinc and sulfur containing lumps in one early work have been investigated previously, and the mechanism of formation is reassessed. Paint samples are examined using optical microscopy, scanning electron microscopy with energy dispersive X–ray analysis, X–ray microdiffraction and FTIR techniques. Of key interest are zinc carboxylates, basic zinc carbonate and zinc sulfates as products of deterioration. No evidence is found to support the presence of crystalline zinc sulfate. Layered basic zinc salts incorporating carboxylate, carbonate and sulfate moieties are proposed as an alternative. Hot, humid conditions and pollution levels in Vietnam coupled with paints containing zinc oxide of different grades and the presence of unpigmented medium or size layers are significant factors in the condition of these paintings