The photo library has a collection of negatives from the 1950's which are undergoing an unstoppable process of self destruction. They are made from a dodgy type of cellulose acetate film, which is inherently unstable and breaks down catastrophically in just a few decades. The film starts to go crinkly, cracked and brittle and gradually falls apart – giving off a powerful stench of vinegar in the process. The negatives become very fragile and of course the image is eventually lost. Here are two of them:
This type of degradation is called "vinegar syndrome", and it is very depressing for a conservator because there is nothing that can be done to save these negatives in the long run. Fortunately the process can be slowed down quite a lot by storing the negatives in a freezer, which buys time to get the images transferred to a safer material (by scanning or copying).
The negatives need special packaging to protect them in the freezer, and to control the humidity around them. Freezers can make things damp (think of all that ice build-up inside) and when you take an object out of the freezer, water in the air condenses on the cold surface and can cause staining or damage. Photo libraries all over the world have the same problems with vinegar syndrome negatives, so conservators have come up with a nifty system of packaging the negatives to protect them against these problems. Nick Burnett of Museum Conservation Services in Duxford is an expert on this and very kindly gave me lots of useful advice.
The picture library has almost 3000 negatives which needed to be packaged and frozen. Here they all are on a trolley, waiting to be put in order. Luckily the smell does not come across in the photo – it was pretty eye-watering:
Each negative has its own little envelope made from very pure "silver-safe" paper which will not harm the delicate chemistry of the image. The negatives are sorted into large and small formats and arranged in number order so they can be found easily. Then they are packaged in small groups of 10 or 15. Each package contains a group of negatives in their paper envelopes, all held in a sealed polythene bag. Outside the bag are 2 pieces of archival card which are dried out in an oven for 5 minutes. The idea is that the super dry cardboard will absorb any moisture which comes into the package from the freezer before it affects the negatives. Here I am drying batches of cardboard in my oven at home (Obviously I cleaned the oven first – probably not before time!):
Drying the card took a couple of hours as there were 400 pieces and they had to be laid out on the oven grilles in single layers.
All these things are put into an envelope labelled with information about the negatives in the package. On the spine of the envelope is a little blue square of humidity indicator paper. This changes colour to lilac or pink if the relative humidity inside the package goes above 50%, so you can tell at a glance if any of the packages are getting too damp inside. A final polythene bag seals the whole lot up into a moisture proof package. Here are the packages lined up like books on a shelf, with the blue indicator squares clearly visible:
If the indicator goes pink, all you have to do is dry out the card again and replace the outer polythene bag, and the negatives can be refrozen. The packages can last for up to 19 years before you have to re-dry the card in all of them.
The packages are now all in a special lockable spark-proof freezer (it needs to be spark proof because the negatives are flammable):
Shortly after I finished repackaging the vinegar syndrome negatives, we were very lucky to acquire the extraordinary Scott negatives. These do not have vinegar syndrome, but freezing them in exactly the same way will preserve the images for ten times longer than storing them at room temperature. So as soon as they have been cleaned they will join the other negatives in the freezer.