Acetate-Based Films: A-D Strips from A to Z
Hi! I am Shahed Dowlatshahi, an almost-graduate of NYU Tisch’s Moving Image Archiving and Preservation (MIAP) 2-year MA program. I have been working as a Media Preservation Assistant at the Media Preservation Unit (MPU) of NYU Libraries’ Barbara Goldsmith Preservation & Conservation Department for the duration of my studies. In the first weeks of the spring 2018 semester I, along with fellow MIAP student Danielle Calle, and Kate Philipson of the Archives and Public History program, completed an inventory of and measured acid-deterioration levels for all motion-picture films stored in the media vault in Bobst Library.
figure 1. Media Vault, Barbara Goldsmith Preservation & Conservation Center
The Media Preservation Unit is responsible for the conservation and preservation of all audio-visual media including motion-picture film as well as legacy audio and video tape formats held by three special collections repositories: Tamiment Library and Robert F. Wagner Archives, Fales Library, and University Archives. Between these three repositories, there are thousands of rolls of film in a variety of formats and a wide range of conditions. Many of these films are stored in a climate-controlled vault with compact shelving, overseen by MPU staff.
figure 2. Shahed Dowlatshahi (MIAP 2018) working in the Media Preservation Vault
Generally speaking, film is made of a plastic base and emulsion coating. There are three types of film classified by the type of plastic base: nitrate, acetate, and polyester. Acetate-based films, which comprise a large majority of our collection, are prone to deacetylation, a chemical reaction inherent to the material and exasperated by high temperatures and humidity. Known more widely as vinegar syndrome (the acidic byproducts of the deterioration cause a strong vinegar odor), this common form of acetate film deterioration causes them to become brittle, shrink, and shed emulsion (figure 3). The film preservation community has been aware of this problem and working to address it for decades. The chemical reaction which causes the deterioration is constantly ongoing and irreversible. But its rate can be slowed down considerably in cold and dry conditions, which is the number one way to prevent deterioration or keep afflicted films from further damage.
Figure 3. Film in the most advanced state of vinegar syndrome.
While the “smell test” is a strong indicator of whether or not a film is suffering from vinegar syndrome, the odor is usually detectable only at the later stages of deterioration. The most commonly used tool to quantify deacetylation, even in early stages, are A-D strips developed by the Image Permanence Institute (IPI) in Rochester, New York (figure 4). When used according to IPI’s guidelines, the blue dye-coated paper strips indicate the extent to which a film suffers from vinegar syndrome by changing color to yellow, on a range from 0 (least deterioration; the strip remains blue) to 3 (most deterioration; strip is completely yellow). A single strip is placed inside a can of film, preferably in contact with the film material (figure 5), for at least 24 hours but up to 6 weeks, depending on the climate conditions in which the film is stored. The colder and drier the climate, the longer the strip must remain in the can before it can be used for an accurate reading.
Figure 4. IPI’s package for quantifying film base deterioration: User’s Guide, A-D Test Strips, and pencil with reference chart.
Figure 5. Placing a new strip in can so that the strip is in contact with the film.
During February and March of 2018 we embarked on a project to assess the level of vinegar syndrome for all the films stored in our Media Vault using IPI’s AD-Strip testing method. During the process we found it necessary to conduct a comprehensive inventory of all films in the vault as well. What follows is a summary of this work.
Our first step was deciding how long to leave the strip in a can before reading the strip color. Following IPI User’s Guide, we decided on a minimum of one week based on the temperature and humidity of our vault. The next step involved the placement of the strips–which should be handled as little as possible by bare hands while doing so as body temperature can affect the readings. Starting from one end of the vault and working towards the other end, the strips were placed in every film can, while simultaneously recording the unique identifier, shelf location, and the date of strip placement for each can.
While ideally all films would receive a strip on the same day and all would be read on the same day a week later, this was not possible due to staffing constraints and schedules. However, by recording the date when each can received a strip and planning in advance, we ensured that our test results were as consistent as possible across the collection. While the placement of the strips can be accomplished by one staff member, when time came to read the strips and record the data, it was helpful to have at least two people, one to open cans, take strips out and read them and another person to record the data using a tablet or laptop. The data recorded at this stage included the date which the results were read for each can.
Because the process of reading the strips and assigning a deterioration number according to their color is somewhat subjective, when possible we arranged for the same person to read all the strips so as to ensure some degree of consistency across the data. While IPI provides a reference chart in the form a pencil (figure 6) which strips can be measured against, we found the usage of this pencil problematic. The colors displayed on the reference pencil are not accurate matches with colors displayed by used strips. In addition, while the pencil displays 4 reference colors meant to indicate readings of 0, 1, 2, and 3 this ignores the many shades of color in between these four. Thus, assigning an accurate and objective value to a used strip presented a challenge that needed to be addressed during this assessment.
Figure 6. IPI’s reference chart for reading used A-D strips
One method that proved helpful in increasing consistency across readings over time was to create a reference ourselves as we accumulated more and more used strips. Through this method, we believe that the readings became more consistent as the assessment progressed. This was done by grouping strips into 7 different piles which represented the full range of deterioration in 0.5 increments from 0 to 3. For example, when reading the first few cans using the reference pencil, it was difficult to decide whether to assign a value of 1, 1.5, or 2 to a used AD-strip that indicated deterioration in that approximate range (figure 7). But once we had read more strips, a range could be constructed with the actual used strips to set a comparative reference for further readings (figure 8).
Figure 7. The pencil reference provides two shades of green which are relatively close for the range of deterioration which they are supposed to represent.
Figure 8. By accumulating used strips into piles of similar colors, a comparative reference chart was constructed as the assessment progressed.
Overall, this method of quantifying deacetylation remains imperfect, with the main flaws being the wide range of colors displayed by used strips versus the 4 colors that IPI provides as a reference on their pencil. However, by utilizing AD-Strips we were still able to gain an understanding of the range of deterioration within our film collection, and identify those which are currently not at risk at all (readings of 0 and 0.5), those which are in the early stages of deterioration and should be either stored in a cooler environment or duplicated soon (1 and 1.5), and those which should be either frozen or duplicated immediately (2 and above).
As a next step, we are preparing to freeze films that gave an IPI reading of 2.0 or greater. Researching best practices in this area, we were delighted to learn that other colleagues in the field had similar questions about the recommended supplies and procedures for freezing acetate-based films. A recent thread on the Association of Moving Image Archivists (AMIA) listserv led us to seek out these beneficial resources:
Association of Moving Image Archivists conference presentation by Jean-Louis Bigourdan, 2014.
National Parks Service website, which contains information on cold storage and photographic collections
