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

AP CF logos


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


Some years ago Glamorgan Archives acquired a vacuum press, which has been put to good use recently to package degrading cellulose nitrate and acetate negatives for safe handling before freezing. Conservation staff were just wondering what else the press could be used for when the November issue of the ICON Journal appeared. It featured an article by Hiromi Tanimura on squelch drying books damaged by tsunami water. The squelch method had been developed by Stuart Welch, and was first used to great effect in 2002 when dealing with the aftermath of the Prague floods at the National Library of the Czech Republic.

Squelch sounded like fun! So we decided to research the method further and try it out ourselves. Initial trials were on two modern hard back volumes, library deaccessions. They were put into a bucket which was filled with water and left overnight. The pages of the volumes had been splayed out for the first trial as we wanted the volumes to be as wet as possible.


The next morning the volumes were taken out of the water and as much of the water as was safely possible gently squeezed out by hand. They were then wrapped in bondina (a non-woven polyester fabric), which acts as a release and prevents the volume sticking to the newsprint in which it is wrapped before being bagged and vacuum packed in the machine.

Packing in newspaper

Wrapping in bondina reduces cost as it also prevents any off setting from inks. Any kind of absorbent paper can be used, including printed newspaper, reducing costs as expensive blotting paper is not needed in large quantities.

Vacuum packed

Once the volume and its wrappings have been sealed and vac packed into its bag it compacts into a solid block. Because the volume has become so compact the water is forced out of the boards and text block into the news print. Once the news print is wet the process is repeated with paper or blotters placed between pages as the volume dries. After the initial 4 or 5 changes the paper wrappings and interleavings need changing only once every 24 hours.

The major advantages of this process are that once the volume is dry it still resembles a volume, opening and closing as it should, unlike an air dried volume which will be splayed and thickened. Removing the air removes the risk of mould growth so the volume can stay bagged in its wrappings for a considerable length of time. Compacted volumes are easily stacked for storage taking up much less space. This, along with the length of time they can be left before changing the wrappings, is especially useful in managing a large scale disaster, or if items need to be moved from one location to another.

The only problem we found with this method is that the spines of the volumes are pushed inwards distorting the volume slightly, so that the fore edge of the text block protrudes from the boards. But this may have been because we were using very modern, cheaply bound books. We are currently experimenting with using a former to support the edge in the bag and with older and more sturdy bindings to see if the spine still distorts. Mostly we are enjoying playing with the machine and telling visitors that we are squelching!

Dealing with Nitrate Film at Glamorgan Archives

Archives can hold collections made up of all sorts of materials; everything from parchment, paper, wax or metal seals and photo-reprographics, to negatives made from glass, paper, cellulose nitrate, cellulose acetate and polyester. All these materials are affected by different environmental conditions and degrade in different ways, some of which can pose significant risks, including to human health. One of these in particular is cellulose nitrate film.

Cellulose nitrate film was used from around 1889 to around 1950. Before nitrate film came along, glass plate negatives had been used. These were very expensive and could be quite tricky to handle. Nitrate film helped to popularise amateur photography by making it more affordable for the masses. As a result, most archives have large numbers of photographic negatives, with many made from nitrate and acetate films.

Cellulose nitrate is very flammable and capable of burning even in the absence of oxygen, and even when underwater! Nitrate film is also chemically unstable; the film support gradually turns yellow, brittle and sticky. It emits harmful corrosive by-products with an acrid smell, which cause fading of the silver image, de­composition of the gelatine binder and, eventually, the complete destruction the negative.

Single negative

Recently, a large number of cellulose nitrate negatives were discovered in the strongrooms of Glamorgan Archives.

Negative bundle

On opening the boxes the negatives were found to be degrading and were giving off a slightly cheesy acrid smell. They were immediately removed to the conservation studio and placed in the fume cupboard to ensure that the nitric acid vapour being emitted was contained. Wearing personal protective equipment and using a portable extraction unit it was possible to vacuum pack the cellulose nitrate negatives and move them for permanent storage in the freezer.


The negatives are vacuum packed to protect them from the environment within the freezer, to prevent contamination from anything else that is stored in the freezer, and to prevent the gas that is emitted by the negatives from contaminating anything else in freezer. By storing the negatives in the freezer it is possible to prevent further degradation and prolong the life of the negatives.  Nitrate film requires hot or warm temperatures to self-combust and so being held at cold temperatures will help prevent this.


This is not the end of the story; plans are in place to digitise these items, so that although the negatives may be in danger, the images they contain will be secured for the future.

Dealing with Mould

Last week it was brought home to us how important it is to have good storage conditions that comply with the relevant British and international standards. A box of documents had been requested in the searchroom by our Senior Archivist, and on production it was found that the documents had what appeared to be live mould on them.  At that point I was called in to confirm the finding.  Mould thrives in poor storage conditions with high relative humidity and high or low temperatures, feeding on the proteins in parchment and glue and the cellulose and size in paper.

The box of documents had been kept at an outstore with no environmental monitoring systems or controls. There were areas of damp and massive temperature fluctuations, all threats to long term health of archival material.  Poor storage conditions were a major driver for the relocation of the archive service in 2010.  Outstores had been needed since the 1960s as the former building was filled to capacity, and very few were ideal for the purpose. The good news is that once moved into stable storage conditions mould growth will slow down and eventually die, a process which can take around 5 years or more.  And we are entering our fifth year in the new building with the entire collection on site and in excellent conditions.

Checking boxes for signs of mould

Checking boxes for signs of mould

Just to be safe, other items and collections previously stored in the same outstore area as this box had to be examined. With help from  Amanda (one of our conservation Volunteers) and Mary (who is with us on work experience) I set off on a mould hunt So far we have found signs of mould in 30 boxes.. Once mould is found the box is removed to our isolation area where the mould can dry out before cleaning commences. This has to be done using specialist tools and wearing personal protective equipment as the mould, is not only very dirty but can also be hazardous to health.

Cleaning documents affected by mould

Cleaning documents affected by mould

Mould can be in the documents before they come to us and we now have a system (and the space) for checking all accessions and cleaning and packaging them before shelving them in the strongrooms.  The recent discovery was a reminder of the bad old days and an incentive to maintain new procedures.  Staff are currently checking all boxes in the collection to confirm location and contents.  Conservation needs are also being flagged with mould identification now a top priority.

Users and staff regularly comment on the benefits of being in a purpose built facility.  It’s good to be reminded that the documents needed the move even more than we did!