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Conservation Notes: Preserving history on nitrate film

August 18th, 2014

By Katharine Whitman, Conservator, Photography

The Henryk Ross collection of negatives depict the Łódź Ghetto in Poland from 1939 to 1944, composing a valuable record of the conditions Jewish people faced during the Second World War. As with all film negatives from that period, they are on cellulose nitrate stock, a potentially dangerous medium due to the material’s tendency to release harmful gases when it degrades. Steps had to be taken to stop the deterioration of the negatives, and so they were recently digitally copied and put into frozen storage at the AGO.

What is cold storage?

While cold (between 15C and 3C) or frozen (below 0C) storage can be beneficial for the longevity of some photographs, it is very important that the proper steps are taken to prepare the materials. Cold or frozen storage is not appropriate for all photographic materials, such as photographs on glass, but photographic mediums that do benefit from cold or frozen storage are colour photographs, colour slides and negatives and Polaroid photographs. Always consult a conservator on the proper steps to be taken for putting your photographs into cold or frozen storage.

If you decided to put your photographs into cold storage, keep in mind the following guidelines:

  • triple-bag the photographs using bags that seal to prevent frost or humidity accumulation when the package is removed from frozen storage;
  • insert some sort of material such as thick, good quality mat board between the bag layers to act as a buffer — the three plastic layers act as buffers against the possibility of moisture entering the housing;
  • remove as much air as possible from the bags when sealing;
  • tape shut the seals as another barrier against the ingress of moisture;
  • insert a humidity indicator inside the outermost bag as an early warning of moisture penetration; and
  • when removing the package from frozen or cold storage allow it to acclimatize to room temperature for at least 24 hours before opening the package.

The edge markings on a piece of nitrate film.

Nitrate film

One of the questions photograph conservators get is how patrons should properly store their photograph collection and more specifically, what to do with old negatives. There are a variety of different film types, one of the materials in this area is cellulose nitrate. While it was used for a variety of objects — dice, film and brushes — it is a potentially hazardous and very dangerous material. Motion picture nitrate film is especially volatile and was the cause of many movie house fires in the early 1900s.

Nitrate film was produced between 1889 and 1951. It can be identified by the date of manufacture: we should suspect that most film made in North America before 1951 is nitrate. The film may also be identified by edge markings that will read “nitrate.” However, even without that label, it is best to assume that pre-1950 film not marked with the word “safety” (which replaced nitrate film) is also nitrate.

Now, 60 years after its production, nitrate film will show its age. Deterioration will be exhibited as yellowing, staining, bleaching, stickiness, embrittlement, blistering and — in the worst cases — it may be pungent-smelling or powdery. As nitrate film deteriorates, it gives off highly acidic nitrogen oxide gases that escape into nearby areas, putting staff, buildings and collections at risk. Nitrate film will deteriorate over time, creating health threats such as eye irritation, headaches, nausea, respiratory and skin irritation and vertigo.

It was due to the above concerns that we put the Łódź collection into a specifically designated frozen storage unit at the AGO and, for these reasons:

  • never discard nitrate film into ordinary trash containers or into routine disposals;
  • don’t burn nitrate film, as it produces toxic gases, such as carbon monoxide and nitrogen peroxide that pose severe threat to life;
  • check with the local environmental agency or fire department for safe disposal; and
  • under no circumstances should someone attempt to dispose of nitrate film themselves.

Lastly, and maybe the most important tip of all…
When in doubt, consult an expert! If you think you have nitrate film, seek the advice of a professional.

Curious about Conservation?
If you have a burning question about Conservation, leave a comment below. We’ll do our best to give you an answer in an upcoming Conservation Notes post.

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