Memories of Glass

This week’s article reviews a recent training event for Icon Interns on the conservation of glass plate negatives held at the RCAHMS and describes the process of repairing a plate using a pressure binding method…

Earlier this year, The Royal Commission on the Ancient and Historical Monuments of Scotland (RCAHMS) hosted a training day on the repair of glass plate negatives organised by resident Icon Intern, Marta García-Celma. Other Icon Interns came from all over the country to take part in the training session. The day was split into two parts. In the morning, there were lectures covering the preventative and interventive conservation of glass plates and their digitisation. This was followed by a practical session in the afternoon, where we got to repair our very own glass plate. The lectures kicked off with Tahra Duncan Clark, RCAHMS Photographer, who gave an overview of the plate collection and described the process of the digitising their huge collection of glass plate negatives. Tahra also discussed the use of Photoshop to touch up damaged negatives digitally. The aim here is not to alter the image in any way, but to remove any distracting scratches or cracks that may reduce the image quality. I thought this was a fantastic way to view and use the material, without having to carry out any interventive work. This allows an otherwise inaccessible image to be consulted without having to wait for conservation treatment to be carried out.

Next, Emma Buchholz, RCAHMS Conservator, discussed the identification and preventative care of glass plate negatives. I found the identification of glass plate negatives fascinating and mind bloggling! There are approximately 20 different types of photographic processes produced on glass. There are also multiple variations on these methods, which increases the amount of potential types of negatives to roughly 40. Luckily, we just focused on the two main processes; wet collodion and gelatine dry plates. Wet collodion negatives are characterised by non-standard plate sizes, uneven coating of the emulsion, and a creamy brown colour. On the other hand gelatine dry plates have standardised plate sizes, a uniform coating of emulsion and have a neutral grey/black colour.

Following this, Elizabeth Hepher, RCAHMS Conservator, described methods for the conservation and stabilisation of glass plate negatives. Glass plates can be cleaned on the emulsion side by using a soft squirrel hair brush. The glass side can be cleaned using a solution of 60:40 Industrial Methylated Spirit (IMS) and water applied using a cotton swab. Care must be taken to ensure that the liquid does not come in contact with the emulsion as this can cause damage to the image and binder layer. Flaking emulsion can be consolidated using a 3% solution of gelatine, applied using a small brush. Elizabeth showed us images of glass plates where the emulsion had almost completely delaminated and curled away from the plate. I was amazed that plates which had been severely damaged in this way, could be treated using this consolidation method.

An example of delamination of emulsion from a glass plate

An example of delamination of emulsion from a glass plate

After a fabulous lunch at a local restaurant, we were able to put what we had learnt in to practise by repairing a broken negative. Led by Marta García-Celma, Icon Intern, we carried out a stabilisation technique using a sink mount with a pressure binding. This essentially supporting the broken glass in a card frame with two pieces of new glass on either side of the plate, which is then bound together using tape. First the new pieces of glass are cleaned using a cotton swab and a solution of IMS and water. Next the glass side of the negative is cleaned using the same solution and the emulsion side cleaned with a soft brush. Any flaking emulsion is then consolidated using gelatine. The broken glass plate is then placed in its original arrangement on a piece of unbuffered mountboard.

Icon Intern, Marta, cleaning glass before conservation.

Icon Intern, Marta, cleaning glass before conservation.

The sections of the plate are then fixed together using small pieces of Filmoplast P90. Using the edge of the plate as a guide, a line is scored around the perimeter of the glass on to the mountboard. The plate is then removed and the middle section is cut away, using the scored line as a guide. Next, the broken plate it moved onto the new piece of glass. The cut card mount is then fitted around the edge of the plate. This should be a snug fit to avoid movement of the broken glass pieces in the package.

The broken glass plate negative held together with pieces of Filmoplast

The broken glass plate negative held together with pieces of Filmoplast

The Filmoplast P90 splints holding the brown pieces together can now be removed using a scalpel with a number 25 blade and the second new piece of glass placed on top. A piece of pH neutral white gummed paper is then cut to go around the perimeter of the plate. This is pasted with wheat starch paste and the glass package placed in the centre. The edges are bound by rotating the package on the paper strip. The tape is then smoothed down and the corners are cut to keep it neat. This is left to dry and given one last polish before being stored in a four flap folder.

Broken glass plate negative, before treatment

Broken glass plate negative, before treatment

Glass plate negative, after treatment

Glass plate negative, after treatment

I thought this was a really good technique as it is completely reversible, the package can just be cut open again, but it provides a very study stabilisation of a previously extremely vulnerable object. The whole package seems very solid and protects the plate very well. However, there are limitations to this technique. The added glass on either side of the plate increases the weight and the dimensions of the object, which could be a consideration if storage space is limited. Also, because the package is sealed, a microclimate is formed within the layers, which could potentially cause further damage to the plate. Overall, I thought the day was a really well organised and I learnt a lot. The enthusiasm and knowledge for this subject by the conservators and their openness meant that it was a fun and relaxed, but informative day which I would encourage other conservators to attend if they get the chance!

Emily Hick

Paper Conservator

Centre for Research Collections, University of Edinburgh

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