Today’s blog is guest authored by the wonderful team who have been carrying out conservation work on our glass plates. The conservation of this kind of material is specialist work and we have been really lucky to secure the skills of Sarah Allen and Emma Bonson, who have worked really hard to conserve close to 1000 of our plates over the last 6 months. Sarah recently visited us to deliver a talk to our volunteers about the work they have been doing, and today’s post is the first of a series in which they will outline the process and share some of the challenges and successes of the project on the blog. With thanks to Sarah, and to Emma, for all the work they have been doing and for today’s contribution.
My name is Sarah Allen and I am the photographic materials conservator who was privileged enough to be appointed to carry out the conservation treatment of the Knights-Whittome glass plate negative collection. Together with my assistant Emma Bonson, we have been working on the collection since December 2016, and it has proved to be both a challenging and rewarding project. Having followed the Past on Glass project from the outset and seen many of the amazing images contained within it, we were really excited to be involved with such an engaging collection. As conservators, we often miss out on the images contained within glass plate negatives as we tend to be more concerned with the physicality of the objects (mould, broken glass, peeling emulsion etc…) rather than subject matter – although even we could not fail to notice the large percentage of very impressive moustaches represented in this collection!
A large proportion of the Knights Whittome glass plate negative collection was in very poor condition due to its previous storage environment. Parts of the collection were so fragile that they were completely inaccessible without conservation treatment. The type of damage represented in the collection included:
- The inevitable cracked and broken glass
- Delaminating emulsion (where the photographic image peels off the glass base)
- ‘Blocked’ negatives (where the original negative envelope becomes stuck to the photographic emulsion due to water ingress)
- Mounts/masks (paper masks used to create contrast during the original printing process but would now block out the image during scanning)
Many of the negatives had a combination of the above types of damage, making conservation treatment particularly challenging!
In this blog post I am going to focus on the treatment of one particular type of damage – delaminating emulsion. What exactly is this problem and how is it treated? Well, first it’s worth explaining a little about the objects we are dealing with. The Knights-Whittome negatives are known as ‘gelatine dry plates’, a type of negative where a thin sheet of glass is coated in a layer of gelatine containing light-sensitive silver salts (known as the ‘emulsion’). It is this very thin layer of emulsion that contains the actual image, so if this layer becomes damaged (for example when the emulsion delaminates or peels off the glass base), it renders the object redundant. Normally the bond between the emulsion and the glass is very strong. There are certain circumstances however when that bond becomes so weak that the thin gelatine layer literally peels off it, as can be seen in this image here:
The emulsion that has peeled off the glass base is just a few microns thick and is extremely sensitive to any fluctuations in temperature or humidity, so as you can imagine it is very fragile. To explain a bit how it behaves, it reminds me of those little red plastic fish you used to get in crackers, which told your fortune depending on how they reacted to the warmth and humidity of the palm of your hand!
Treating this kind of damage can be challenging, but the key with all conservation treatments is to understand what causes the problem in the first place. Fortunately, I had carried out an in-depth research project on this type of deterioration a few years ago with colleagues at English Heritage – this problem is not limited to the Knights-Whittome collection and is in fact a common issue in many photographic collections of the same type and era. Our research can be read here or in even more detail here . Essentially we found that delamination occurs when the glass base starts to deteriorate, leaching out alkali salts, leaving the once-smooth surface of the glass extremely porous. This weakens the bond between the glass/emulsion interface and eventually causes the emulsion to delaminate, especially when environmental conditions are less than ideal, as was the case in the storage of the Knights-Whittome collection. This means that consolidation (essentially sticking the emulsion back onto the glass base) wasn’t an option, as the problem would simply reoccur. Also, with such a large collection the treatment had to be practicable too. The main aim was for the treatment was to restore the image as far as possible, whilst physically stabilising the object so that it could be handled safely and scanned without risk of further damage. Emma and I decided that the best course of action was to carry out a ‘flush pressure binding’. An example of this can be seen in the case study below.
Case Study: negative 22006 “Señor Mazzoni”
This negative had a number of issues. The emulsion had lifted across the majority of the surface. It had also fractured in numerous places with smaller fragments becoming loose and folded.
After careful cleaning, the loose and folded emulsion is lightly humidified along the crease edge and then carefully opened out and pressed between bondina (a special type of non-stick but porous material used in conservation), blotting paper and glass weights.
Once flattened, the loose fragments were aligned as closely as possible on the light box. The whole negative was then given a ‘flush pressure binding’ i.e. a new piece of glass the same size of the negative was bound to the original negative using “Filmoplast P90”, a conservation-grade pressure sensitive tape. The tape was then trimmed back to the rebate of the negative to ensure no image was covered up. This results in a much more stable object, with a treatment that can be reversed in the future if needed as no adhesive is used. Especially important in this case is the fact that Senor Mazzoni’s extremely impressive moustache is now revealed in all it’s glory.
In my next blog post I will focus on a different conservation issue in the Knight-Whittome collection – the inevitable broken glass plates. I hope you find it a cracking read!