By Katharine Whitman, Conservator, Photography
Adventures in Photograph Conservation: Cased photos
A photograph can be printed onto almost any surface. While paper is the most common substrate, others include metal, leather, plastic, cloth, canvas and glass, and many of these are represented in the AGO’s photograph collection. This is the first in a series of blog posts that will describe photographic processes and some of the hurdles a photograph conservator has to overcome while working with them. This instalment will cover the more common cased photographs: daguerreotypes, tintypes and ambrotypes. We’ll get to some of the more unique processes, such as the opaltype and pannotype, in another post.
Examples of these processes are often encased in leather-coated wood or sometimes in what were called “Union Cases,” which were made from a thermoplastic material. While some of the cases were larger, most were small enough to be held in one hand: these were precious, portable objects, often lined with silk or velvet, and many times contained the only existing photograph of an individual.
With the introduction of the daguerreotype in 1839 by Louis-Jacques-Mandé Daguerre (1787–1851), the dawn of photography, as it related to the public, had arrived. A daguerreotype is a photograph that consists of a mercury amalgam on a silver electroplated copper plate (right). The distinguishing visual characteristics of a daguerreotype are that the image is on a mirror-like surface of metallic silver: it will appear either positive or negative depending on whether a light or dark surface is being reflected in the image. The image was often also coloured with pigments to give it a more life-like cast. As an example of employment following the development of new technology, many of the artists who did this work were former miniature painters. With the introduction of photography in 1839, the demand for hand-painted miniature portraits declined drastically, and so it become common for photographers to have re-touchers and colourers on staff to apply the pigments.
After the daguerreotype’s public introduction and adoption, many scientists started working on other, more economical photographic processes. In 1851, Frederick Scott Archer (1813–1857) introduced the collodion process. Ambrotypes and the tintypes (examples at left) are both collodion-based processes, the former being on glass and the latter on a thin sheet of darkly painted metal, usually tin or a ferrous material. The collodion in these processes is derived from solution of pyroxylin, or gun cotton, dissolved in ether and alcohol. Once coated on a piece of glass or metal, the collodion is sensitized in a solution of silver nitrate and exposed in a camera, and the plate is developed, fixed and allowed to dry. The resulting photograph is then varnished to prevent deterioration of the image. These photographs were much more resilient than daguerreotypes and — though conservators today would warn against it — some people would send their tintypes through the mail without a case, unconcerned about damaging the photograph.
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