Transparent varnishes on copper alloys dating from the 19th century: characterization and identification strategies

Many varnished copper-based artefacts dating from the 19th century can be found in museum collections. Although conservators deal on a daily basis with these surface finishes, few studies on this topic have been conducted during the last few decades on European objects. A more thorough understanding of these historical coatings would be helpful to establish accurate diagnoses and to contextualise the results with respect to the historical written sources. This paper presents the first results of the LacCa (Lacquered Copper Alloys) project currently being undertaken by an international multidisciplinary team. LacCa aims to develop a methodology that conservators can apply to identify and preserve these coatings. To this end, both historical objects and ancient varnish recipes have been studied. In a first step, the identification and characterisation protocol was validated using mock-ups, the results of which are presented in this paper.