Tuesday, 4 November 2014

Training: Preserving historic photographs

In September I spent a day at the British Library Centre for Conservation on a training day on  preserving historic photographs. I wanted to go on this course as I have a lot of photographs in some of my collections at work, and, although I already knew some of the basic principles of caring for them, I wanted to learn more and check I was doing the right thing.

The Centre for Conservation (slightly dwarfed by all the building work behind it)

The day started with introductions all round. The other participants were from a range of organisations, including libraries, archives, museums and some freelancers. First of all was an introduction to the history and identification of photographic processes. This took us through the very beginnings of photographic techniques, and examples of each were passed round the room for everyone to look at in more detail. It was important to cover all of this, as photography initially was very experimental so a variety of materials and techniques were used, some of them overlapping with others - more like evolution than processes in isolation. Of course, as photography was a new thing, nobody initially knew what purpose it would have, so techniques for producing multiple images were one development (by Fox Talbot), as were those aiming to produce one image to replace the miniature (by Daguerre) were another. There is an overview of techniques in the British Library's guide to preserving historic photographic material, available on their website.

Of course, this variety of techniques and materials does not make life easy for those caring for photographic collections now!

We then moved on to conservation problems and solutions, and, again examples were passed around so we could see the type of damage caused. This is a relatively new field of conservation, developed in the 1980s once scientific analysis had developed, although from the earliest days of photography, it was known that there were problems with the stability of silver processes.
The emphasis is very much on correct preservation: because photographs are multi-layered, this makes conservation very difficult, so it is best to avoid creating problems in the first place, than having to deal with them later.

Conservation problems may be caused by:
  • Using fix repeatedly, or not washing properly, which produces sulphur on the photo
  • Atmospheric pullution
  • Storage materials
  • Deterioration of the edges in images made using silver. As the air gains access to the photo over time the edges deteriorate with a mixture of oxidation and sulphurisation.
  • Printed out/paper prints may have very fine surface particles which may react with other things (e.g. sulphur will make yellow areas yellow more and fade first). This type of damage is irreversible.
  • Whereas cyanotype photographs fade with exposure to light, but the colour eventually returns once they are returned to dark conditions. These will also fade in alkaline conditions, such as an acid-free folder.
  • Glass plates breaking
  • Tintype metal supports will rust and the emulsion peels away from the support. Nothing can be done about this.
  • Albumen has a tendency to curl inwards and surface cracks if it's flattened. The molecules are very affected by fluctuations in environment.
  • Platinum prints - platinum is a catalyst so will cause any facing paper to degrade, e.g. in an album.
  • Gelatin is very vulnerable to moisture and mould, as well as being popular with insects.
  • Mouse damage is possible in a photographic collection, though it is less likely than in other collections.
  • Chromagenic prints are not stable when exposed to light, so ethical decisions need to be made about how to copy these as the original changes over time.
  • Cellulose nitrate has a relatively low temperature (38°C) at which it is flammable. It also produces its own oxygen when it burns, so it is very difficult to extinguish flames once it's alight. However, film made with these is usually in good condition and tends not to be unstable as long as it is kept cool. It can give off a slightly acidic gas.
  • Cellulose acetate - unstable and has distinctive smell. The film becomes more brittle, making it unusable. This can happen extremely fast.

Finally, we looked at the preservation of photographs and examples of suitable storage products were passed around. We also came away with catalogues from vendors.

The first thing to note was that PVC enclosures are very bad indeed! Paper and boards used in storage (packaging and mounts) should have a high alpha-cellulose content, with neutral pH, with undetectable sulphur content and free from other impurities such as metal particles.
Some examples of storage materials include:
  • Photon, supplied by Conservation by Design
  • Argentia, supplied by John Purcell (this is a replacement for the old Silversafe paper, which is no longer available).
  • Melinex/Mylar (polyester), supplied by several different suppliers, including Conservation by Design, Secol and Preservation Equipment Limited. Limited sizes also now seems to be available from firms like Gresswells. Plastics must be free from plasticizer, glaze or coating. Prints with emulsion surface damage or mould should not be put into Melinex.
  • Glass negatives should be stored in purpose-built plan chests as they are very heavy, and this is less risky than using boxes.
  • Glass negatives cannot be stored on aluminium shelving as it isn't strong enough. Shelves should be made from steel with a baked enamel or powder-coated finish.
  • Boxes for storing photographs should be acid-free on the outside as this acts as a filter against acids coming in.
  • Cold storage is worth considering for later film-based material, particularly if colour is shifting. Timecare ringbinder boxes containing Melinex sleeves can be housed in freezer boxes and then stored in domestic freezers. Hollinger Metal Edge produce freezer packaging, although it is hard to get hold of in the UK.
  • Albums - purpose-made boxes of just the right size are now available.
  • Plastazote, which is inert and available in different thicknesses, is good for creating partitions in storage boxes.
Other factors:
Temperature and relative humidity - the graph on p. 8 of the British Library's booklet shows the area that is safe - straying outside this grey area means irreversible physical damage. It is usually easier to lower the temperature than it is to control humidity. Cold storage in freezers is the optimum way to store photographic material for as long a time as possible and it is more important to get something that is deteriorating into freezer storage quickly, than it is to rehouse it in Melinex.
Light - keep an eye on the lux hours per year any photograph is exposed to. The choice is between a higher lux for a shorter period, or vice versa. Some institutions allow for a small physical change to occur in their collections over a 50 year period. UV light is particularly damaging and should be excluded from the building by using appropriate blinds and filters.
Handling - Clean hands are better, but try and handle photographs as little as possible. Avoid using any creams or moisturizers. Do not flatten rolled prints, or use adhesive tape, paper clips, pins etc. Do not eat, drink or smoke near photographs, or use ink to label them. Albums should be supported on book supports.
Storage - do not store anywhere near a photocopier or printer as these give off ozone. Do not keep in a basement or attic. Older wooden cabinets (e.g. 50+ years old) are unlikely to cause any further damage, but be aware that felt linings can cause problems. Lino and paint can both give off fumes.

Interesting fact of the day - historic photographs could have been manipulated, just like modern ones (although not quite as easily). Look out for the same cloudscapes being used repeatedly...

It was a very good day on the course, and I learnt a lot, as well as consolidating my existing knowledge. I think it could have been improved by devoting more time to the preserving photographs element in the afternoon, which was done in a bit of a rush.

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