Friday, 21 August 2015

Frozen Storage for X-rays


In my last blog, I wrote about the deterioration of X-rays in the LHSA collections. This week, I will talk about how we intend to store them to slow down the rate of degradation.

The best way to store X-rays, and most photographic material, is to freeze them. Chemical reactions increase as the temperature rises, and colder conditions slow them down. So, by placing the X-rays in to temperatures lower than 0°C, the rate of deterioration will decrease.
 
A conventional freezer can be used to freeze small collections, but the items need to be properly packaged first to avoid any moisture coming into contact with film. We have decided to use a method recommended by the National Park Service, which uses two barrier layers to protect the photographic material. First the X-rays, which are already packed into inert plastic packages and labelled according to their reference number, will be placed into an archival box. Any empty space in the box will be filled with layers of conservation grade mount board and acid free tissue paper to help absorb any moisture inside the package.

X-rays sealed in inert plastic packages
The box will then be inserted into a tube of Marvelseal® (an aluminised polyethylene and nylon barrier film which resists the transmission of water vapour and other atmospheric gases), and sealed with a strong tape. A humidity indicator will be attached to the outside of this package, so that any moisture ingress can be easily spotted.

This package will then be inserted into a polythene bag which is again sealed with a strong tape. The box is then clearly labelled with its contents and placed into the freezer. A map of the contents in the freezer will also be made, so that the X-rays will be easy to find when needed.

If the X-rays need to be consulted at any point they can be removed from freezer, but will need to be slowly acclimatised to the warmer temperature, to avoid the formation of condensation on the film. To do this the X-rays can be placed into a study box and left in a stable environment overnight to gradually adjust to the new temperature.

This new storage method will increase the lifetime of the X-rays significantly. I hope you think of them next time you open the freezer door!

Have a look at the Media Storage Guide by the Image Permanence Institute for more information on the storage of photographic materials.

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