Historical tintype plates: analysis of supports, japanning layers, and verso varnishes.

The tintype, a wet collodion photograph on a japanned metal support, was a popular type of photographic image in mid-nineteenth-century United States. Tintype plates consisting of a metal sheet with a protective varnish on the verso and a dark colored japanning layer on the recto were commercially available in different colors and surface textures. Although millions of plates were produced, there is little information regarding the materials used to create them. To address this lacuna, the metal supports, japanning layers, and protective verso varnishes of 226 historic tintypes were analyzed to identify the support metal, binders, and pigments. The predominant component of the japanning layers is drying oil, or drying oil with Pinaceae resin; shellac, sandarac, and camphor also occur. The verso varnishes are primarily drying oil and Pinaceae resin, and the presence of these two materials permits comparison of relative extent of oxidation and illustrates that factors other than age impact these metrics. Carbonaceous blacks and iron oxide pigments are common japanning layer pigments, but asphaltum was minimally used. Cross-sections reveal that some japanning layers are a single layer, while others contain multiple coats indicating a complex manufacturing process. The materials used and manner of coating applications differ from the contemporaneous literature and may be manufacturer dependent. [ABSTRACT FROM AUTHOR]