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Conservation Notes: Piecing together the past

November 25th, 2014

Figure 1: Examples of modern (left) and historic glass.

Figure 1: Examples of modern (left) and historic glass.

By Katharine Whitman, Conservator, Photographs

Picture this: you’re in your grandfather’s ancestral home. Under a stack of dusty photo albums you discover a small book-like box with a tiny metal clasp. You open it and find a photograph of a man with familiar features sitting stiffly before a painted landscape. It dawns upon you that it must be some distant relative, perhaps your great, great grandfather. Upon closer inspection, you realize that the image is in fact printed on a sheet of glass and that glass is cracked in two. What do you do?

As the AGO’s conservator of photographs, I’ve spent the past 10 years facing very similar situations. I have conducted research and taught workshops on a much neglected part of photography: the conservation of photographs on glass. This includes ambrotypes, opaltypes, wet plate Collodion, gelatine silver on glass and a host of other processes, many of which are represented in the AGO’s photography collection.
One of the pressing concerns in photograph conservation is how to deal with broken photographs on glass. Should they be repaired? Can they be repaired? In trying to answer these questions, a conservator must consider a host of factors, including: when the photograph was produced, the nature of the glass used, what photographic process was used and the value (monetary, sentimental or cultural) of the piece.

Imagine you needed to repair a sheet of glass that had broken in two. The logical way to do it would be to lay the two fragments on a flat surface, butt them against each other and glue their edges. However, it’s often not that simple.

Figure 2: A side view of historic non-planar glass.

Figure 2: A side view of historic non-planar glass.

Due to the glass-making processes prior to 1950, the sheets of glass used in photographic processes were not truly flat. This “non-planar” glass poses problems for conservators. Figure 1 is a comparison of modern glass, on the left, and pre-1950 historic glass, on the right. A bank of ceiling-mounted fluorescent lights is reflected in their surfaces. The reflection on the modern glass is undistorted because the glass is flat and the reflection on the historic glass is distorted because the glass is slightly wavy. You may have seen windows of old houses that look wavy and noticed how distorted any reflections look; that effect occurs because the glass is non-planar (Figure 2). This poses problems when repairing broken photographs on glass because when laid flat, the shards cannot be aligned properly. With this in mind, an innovative solution had to be found to accomplish the reassembly of broken historic photographs. The whole point of most photographs is to be decipherable, and if a photograph on glass is not in one piece, it loses its meaning and its full impact on the viewer.

Figure 3: A vertical assembly setup.

Figure 3: A vertical assembly setup.

The solution I determined, in association with the George Eastman House and the Corning Museum of Glass in Corning, New York, is an adaptation of a method created by Stephen Koob of the Corning Museum. It is the “vertical assembly” method, wherein the broken photograph on glass is assembled vertically, rather than horizontally. In this method, it is essential that the main shard is positioned perfectly aligned with gravity (Figure 3). Because glass is so brittle, it breaks very sharply. This results in a clean break, a shattering effect or a combination of the two. Vertical alignment ensures that the constant of gravity will pull the shards into position. This method of shard assembly is a completely new concept in photograph conservation.

There are many nuances to the repair of broken historic photographs on glass, and it takes a lot of experience and practice to master. If you have a broken photograph on glass it is best to contact the AGO conservation department for a referral to a conservator.

Curious about Conservation?
If you have a burning question about Conservation, leave a comment below. We’ll do our best to give you an answer in an upcoming Conservation Notes post.

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