How to

24 October 2016

Using Cold Storage to Preserve Precious Film

Typically, when people think of items going into cold storage, they jump to the obviously perishable, such as food. However, some objects need to be kept for such a long period of time that they begin to decay, even if we wouldn’t immediately think of them as degradable. Films and photographs, for instance, are important cultural artifacts that, when stored long enough, will begin to warp and decompose. Since the first introduction of photography in the 1830s, a huge range of photographic materials and methods have been tested, but one thing remains constant: cold storage helps preserve them all. This is a welcome development indeed, as it’s estimated that 90% of all American silent films made before 1929 and 50% of American sound films made before 1950 have been lost.

The science behind refrigeration is simple: lowering the temperature of a substance slows the molecules within it enough that chemical reactions take place at a lower frequency, reducing the rate of decomposition. It’s not just the temperature that must be monitored for proper cold storage though, as humidity must also be strictly controlled, with drier conditions making for slower decomposition.

With regards to film, The Image Permanence Institute at Rochester Institute of Technology developed a decomposition timescale considering the effect of temperature and humidity combined. To give an estimation of the huge effect proper cold storage can have, at an extreme 35°C temperature with a relative humidity (RH) of 80% the average film could last about 4 years. Bring the temperature down to 2°C and the RH to 20% and that same film could survive for 1250 years. This emphasises the critical importance of proper cold storage when preserving delicate cultural artifacts such as film.

Film is so susceptible to decay as it is largely made from cellulosic plastic materials, which break down rather easily. On top of this, the chemical reactions driving this deterioration are autocatalytic, meaning that products of chemical degradation accumulate and catalyse further deterioration. Once deterioration starts, the rate of chemical activity continually gains momentum, meaning your whole collection could begin to decay in a feedback cycle.

Extreme nitrate decomposition
To prevent this, cold storage of film can take place in climate-controlled storage rooms or in special freezers. Preparation for storage can be quite a time-consuming process, as the film must be specially packaged in coated boxes to ensure maximum preservation and to avoid the spread of gaseous decomposition by-products. On top of this, it is generally recommended to make digitised copies before doing packaging, which can add a lot of extra time onto the process.

All of this needs to be completed before it’s too late and irreversible damage is done. The University of Texas in Arlington, for example, holds a collection of 5 million historical negatives, providing a filmic history of North Texas going back to the 1920s. One day, however, they noticed a vinegary smell emanating from their archives (when acetate film breaks down one of the by-products is acetic acid, the key ingredient in vinegar). The decay became a pressing issue, with an expert estimating that 10 to 20% of the film would become unusable within 5 to 10 years, with the rate only increasing after that.

The university acted, deciding to build a 940-square-foot vault that maintains near-freezing temperatures, and a smaller “cool room” for materials that can’t handle the extreme cold. This specific case study shows just how much time and expense setting up cold storage can take, though, with years of planning and raising the $810,000 needed for the project, which took 6 months to construct. The process of then filing all of the photographs has already been going for several months, and is expected to take a further year. However, it’s definitely worth the expense, as the facility is projected to save the film for a further 500 years. The same storage technique is used in most countries, such as at the BFI’s £12m facility.

Overall, the preservation of film marks an unexpected but vital use of cold storage technology. Though quite a costly process in both money and time, it is difficult to put a price on our cultural heritage. In a 1926 article in The New York Times, Films Put on Ice for Fans yet Unborn, Will H. Hayes, early president of the MPAA and namesake of the Hayes Code for film censorship extolled the necessity of film conservation so that ‘schoolboys in the year 3,000 and 4,000 A.D. may learn about us.’ The technology is not quite there yet, but 500 years is a good start, and plenty of time to work something new out!

Sam Franklin

With a master’s in Literature, Sam inhales books and anything readable, spending his working hours reformulating the info he gathers into digestible articles. When not reading or writing, he likes to put his camera to work around the world, snapping street photography from Stockholm to Tokyo. Too much of this time spent in Japan teaching English has nurtured a weakness for sashimi, Japanese whisky, and robot cafés.