Although we have all been working from home, the collections in our storage areas have to be physically checked now and then and maintained in a safe state. One of the areas that needs visually monitoring every few days (as it is not linked into the Building Management System) is the Cold Storage room which contains three laboratory freezers which house our most vulnerable moving image films and film-based photographs.  Please see previous blog posts here and here.

Routinely, every three months, the freezer doors are opened and the humidity indicators are checked – these are small pieces of cobalt chloride paper within the plastic packages which remain blue when the humidity is in the safe range.  If any begin to turn lilac that means that the humidity buffer enclosed in the package (dried board or silica gel) is starting to get used up and therefore needs to be reconditioned.

I carried out this check and, as normal, found a few that were ready for reconditioning.

Materials laid out on a table: boards, silica gel, plastic bags, humidity indicators and vacuum cleaner

This image shows the materials used in the process – boards, silica gel, plastic bags, humidity indicators and vacuum cleaner.

The process of reconditioning involves

    1. Taking the items out of the freezer, placing them in a cold box and allowing them to slowly warm over 24 hours in our main storage area
    2. Removing the old outer plastic bag and the partially used up silica gel (or dried boards)
    3. Adding new fully dried out silica gel (or boards dried out in an oven) and then returning to a new plastic bag which has been checked over for any holes.
    4. Removing excess air with a vacuum and carefully sealing up the plastic bag.
    5. Returning to the freezer.

A circular metal film can lying open on a table. Inside there is a film reel inside a plastic bag, and two silica gel packets.

Here you can see an open film can with the empty space filled with dried silica gel before being sealed up. Note the actual film itself is protected from the dry environment by being sealed up in another plastic bag. (Fig. 1)

And here are three of the finished/reconditioned films ready for return to the freezer. Note the blue humidity indicator. (Fig. 2)

It was a pleasure to be in the Archives Centre carrying out this essential task and hopefully, in three months time, when the next check comes around, things will be more normal…

Sarah Lewery

Senior Conservator