The National Library of Scotland has in its holdings an amazing collection of photographs and photographic albums. The collections tell the story of the medium before its official announcement in 1839, its first use to illustrate books, and its rapid development throughout the 20th century. The preservation of photographs requires specialized knowledge in order to understand their deterioration mechanisms and in most cases, their unstable and fragile nature. For this reason, identification and characterization is fundamental, and this can be achieved by taking a closer look at the structure of the objects. Thanks to a generous donation, the conservation department has recently been equipped with a new, high- tech stereomicroscope (Leica S8APO), which will assist in identifying and characterizing this material.
Since its invention, the development of photography has introduced a large number of processes using different materials and chemicals. This diversity of the photographic medium is mirrored in the collections of the library, and provides not only a visual history but also technical information about photography’s development.
An example of the first successful form of photography in the collection, the daguerreotype (1839-1860), is a portrait of a couple by William Edward Kilburn (figure 1). The daguerreotype process gives a unique photograph on top of a copper plate covered with a very thin layer of silver. The silver plated copper was sensitized to light using iodine vapours and after the exposure in the camera; the image was developed with mercury vapours. Although an experienced eye can easily identify the process with the naked eye, looking at it under the stereomicroscope we can observe the hand painted details on the woman’s dress (figure 2), and going into very high magnification, we can even examine the individual silver-mercury amalgam particles that form the image (figure 3), admiring the very fine detail of this photographic process.
The silver gelatine print (figure 4) is the most common black and white photographic process of the 20th century. An interesting characteristic about matte surfaces of this process is the matting agents (usually wheat starch grains), which were used to bring down the glossiness of the gelatin. These grains are visible under the stereomicroscope (figure 5). Paper fibres in these prints are not visible due to a thick layer of white pigment (baryta), which covers the paper under the image and provides an additional identification clue.
Using high magnification is also helpful to identify colour photographic processes. Figure 6 shows an 80 times magnified detail from a colour print, part of a collection of photographs from a religious festival in the Kulu Valey, India (figure 7). The image shows the individual cyan, magenta and yellow dye particles, characteristic of the chromogenic colour process. Early prints of this type of process are particularly vulnerable to light fading and colour change.
Sophisticated software has been installed on the computer, which is connected to the camera of the stereomicroscope and allows us to view on the screen live images and take pictures. This can facilitate any treatments or tests that need to be performed on very small areas of an object (figure 8) and give the possibility to record information that we would not be able otherwise. For example, using the software we can measure with extreme accuracy part of an object in a micro-scale and use this information to evaluate the result of a treatment. Further equipment, like ultraviolet (UV) or transmitted light, can be added to the main body of the stereomicroscope and expand the examination possibilities.
The new stereomicroscope in the library’s conservation studio has already made a big contribution to understanding the various materials found in the library’s collections and has become an indispensable every day tool for the conservation staff. Donations like this support the work of the conservation team and allow enhancing the research possibilities on the library’s collections.
For more information on the Photographic Collections of the National Library of Scotland visit https://www.nls.uk/collections/rare-books/collections/photographs
For more information on the identification of photographic processes go to http://www.graphicsatlas.org/