The National Coal Board collection at Glamorgan Archives contains around 4000 glass plate negatives, documenting coal mining in South Wales. These glass plates illustrate a range of subjects concerning colliery life above and below ground. As glass plates offered more dimensional stability in comparison to plastic supports, they are often found in large industrial collections containing lots of technical imagery and reproductions of maps and plans.
Although the supports provide more chemical stability than their cellulose nitrate and acetate counterparts, glass presents its own problems. Deterioration can occur in glass, particularly older glass, because it contains water sensitive components which can leach out in fluctuating environments and closed microclimates. As well as damaging the glass, this process of degradation can also affect the photographic emulsion.
The main issues affecting the glass plate negatives in the NCB collection include broken plates and damaged emulsion. The broken plates have been given new housing which cushions and separates the shards and allows for the possibility of further treatment in the future. The plates with damaged emulsion need to be repaired before they can be digitised, re-housed and accessed by the public, making their conservation a high priority.
In October, the Art Gallery of Ontario, in Toronto hosted a workshop on the conservation of photographs on glass, which project conservator Stephanie Jamieson attended, thanks to generous contributions from the Archives and Records Council Wales, the Clothworkers’ Foundation and the Anna Plowden Trust. This three day course was run by Katherine Whitman, Photograph Conservator at the AGO and Greg Hill, Senior Conservator of Archival Materials and Photographs at the Canadian Conservation Institute. The course began with a day of lectures on the chemistry and nature of glass, the history of photography on glass and the identification of techniques and materials. Talks were given by Stephen Koob, Head of Glass Conservation at the Corning Museum; Sophie Hackett, Curator of Photography at the AGO and Katherine Whitman.
The second day focused on teaching repair techniques and storage recommendations. There was also time to discuss the specifics of individual collections and share experiences of working with this type of material.
On the final day, the course participants got to test out the techniques they had learnt in the AGO’s conservation studio. This involved repairing broken glass plates and consolidating emulsion. One repair method used sticky wax to hold the fragments of glass in place while assembling vertically in a vice. Adhesive was then applied to the break using a piece of steel wool on a stick.
To consolidate the damaged emulsion, controlled humidification was applied to the lifting flakes to relax the gelatine before adhesive was brushed onto the glass underneath. Light pressure was then applied through bondina with a bone folder and the flake was left to dry under weight.
This workshop was extremely applicable to the conservation issues present in the NCB collection at Glamorgan Archives. The next stage will be to test and perfect these repair techniques before starting work on the damaged glass plate negatives.
Stephanie Jamieson, Glamorgan’s Blood Project Conservator