Conserving Photographs on Glass

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.

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An example of damaged 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.

trying the vertical assembley method

Trying out the vertical assembly method

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

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Glamorgan’s Blood Preserved on Glass

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The National Coal Board collection at Glamorgan Archives includes a large amount of photographic negatives on both plastic and glass supports.

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The glass plate negatives, approximately 5440 in number, feature a range of subjects, including images of tunnels, miners in action, equipment, pit ponies, medical centres, social events and other varied content.

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As part of the Glamorgan’s Blood project, this photographic material will be catalogued, cleaned, digitised, conserved and re-housed, allowing public access to these images.

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While the majority of the glass plate negatives simply need cleaning prior to digitisation, some display more extensive conservation issues.  A number of the plates are broken or have lifting or highly damaged emulsion (fig.5).  These issues will require more supportive housing solutions or more intensive conservation treatment.

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Figure 5

Undamaged but dirty glass plate negatives require cleaning prior to digitisation and re-housing.  Surface dirt on these items can contribute to long term deterioration and be visible on the digitised image.  It is important that the plates be properly cleaned before any further steps in the preservation process can be taken.

To clean the plates, first an air-puffer is used to remove loose dust and dirt on both the emulsion side and the glass side.  By using this tool, the emulsion side of the plate can be cleaned without risk of abrasion.  Next, cotton wool buds wrapped in fine tissue and dipped in a solution of water and ethanol (50:50) are used to remove dirt and grease from the glass side of the plates.  A final wipe, using a dry cotton wool bud, removes any streaks.

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Figure 6

The cleaned plates are then re-housed in folders made from material up to PAT (Photographic Activity Test) standards.  We use different sized folders for the varying plate formats to ensure a good fit (fig.6). The original packaging for these items was glassine envelopes, which is a type of highly calendared paper often found used for the storage of photographic negatives. Glassine is an inappropriate storage material as it yellows over time and can damage the photographic emulsion (fig.7).

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Figure 7

Once cleaned, the plates are scanned and a positive image is created.  This will then be added to the Archive’s catalogue.

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Figure 8

Broken glass plate negatives require housing which both supports the fragments but also keeps them separate to ensure the delicate emulsion is not damaged through abrasion between the glass shards.  The new housing incorporates cushioning plasterzote foam within an un-buffered card enclosure.  This new enclosure allows the negative to be safely stored and, if necessary, viewed without removing the individual shards (fig.8 & 9).  This simple housing solution can provide either temporary or long term storage, allowing for further repair treatment to be carried out in the future.

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Figure 9

The broken negatives will also be scanned and digitised, reducing the need for handling while at the same time ensuring public access to these wonderful images.

Stephanie Jamieson, Glamorgan’s Blood Project Conservator