“Darling, forever is a long, long time, and time has a way of changing things.”
—Big Mama, The Fox and the Hound.
Kristen chose that quote to begin her talk, and indeed it is true of all objects in cultural heritage institutions. Her particular institution, the Walt Disney Animation Research Library is home to over 60 million objects, including animation drawings, pencil story sketches, watercolors, maquettes, and animation cels, the latter of which make up approximately 10% of the collection. Animation cells are transparent sheets of material, usually celluloid (nitrocellulose), cellulose acetate, or polyester that have been inked on one side, and then painted with gum based media on the other. These materials, particularly cellulose nitrate and cellulose acetate, are highly prone to degradation, so the library partnered with the Getty Conservation Institute to investigate the material nature of the cels and determine if the environmental conditions in the library (62-65 oF, 50% RH) and the microclimate packaging used were sufficient to protect these objects.
Phase one of the project involved investigation of the material nature of the animation cels, addressing the questions: what is the base polymer of the cel, what plasticizers are present and in what quantity? They initially used a portable FTIR and non-destructively analyzed 200 cells dating from 1937-2003, and then chose 80 of those items to do more in-depth, microdestructive GC-MS analysis on. In their initial survey they found cellulose nitrate, cellulose diacetate, cellulose triacetate, and polyester as the base support material. Surprisingly, the material used for a single production would not necessarily be the same; it seemed that the artists used whatever was at hand. Due to the limits of the talk time, Kristen chose to focus on the acetate films for the rest of her talk.
The cellulose acetate cels were found to contain 11 different plasticizers, 6 different types in the diacetate and 5 in the triacetate. These included triphenyl phosphate and a variety of phthalates including dimethyl phthalate (DMP) and bis(2-methoxyethyl) phthalate (DMEP). The plasticizers accounted for 12-19% by weight of the diacetate films and 8-14% by weight of the triacetate films. The diacetate films had an acetyl content of 35-41%, while that of the triacetate films was 43-45%. They are not sure if the range is due to partial hydrolysis or variability in manufacturing. There was no correlation between acetyl content and production year. However, it did appear as if the older films might be a bit more yellow, but more work needs to be done to determine if this is a viable observation.
Phase two was assessing the environmental conditions, or as Kristen said quoting Mufasa from The Lion King, “Everything you see exists together in a delicate balance.” Since this portion was focusing on cellulose acetate cels, Kristen referenced Image Permanence Institute guide for the storage of acetate film (https://www.imagepermanenceinstitute.org/webfm_send/299) and pointed out that the library’s storage conditions were outside of the optimal range recommended by the IPI (50 oF or lower, 20-50% RH). However, the cels are composite materials and it is unknown how the gum based paints would react to lower temperatures and what kind of mechanical stresses might be induced by those conditions, so they feel that the chosen conditions are a good compromise. However, belief isn’t the same thing as actual data, so they performed a survey using AD strips, looking at four vaults and 8 different locations. The strips were assessed after 8 and 96 hours and only one location, next to the Bambi collection, was off-gassing acid. They are planning on investigating that collection further to zero in on the problem.
The library also stores and exhibits the cels in passé-partout packages that include a window mat, the cel (usually hinged with Japanese paper and methyl cellulose), matboard, and a sheet of Artsorb conditioned to 50% RH. They include a RH strip to be able to easily determine if the Artsorb is working. This was supposed to be best working practice but after an exhibition of cels at the Grand Palais, they noticed microcracks and paint delamination and became worried that the package was concentrating off-gassed materials and accelerating the decay of the cels. To try and determine what was happening they extracted gas from a sealed package and analyzed the entrapped air by GC-MS. No acetate (at least above 800 ppb) was detected, suggesting that hydrolysis of the cellulose acetate was not occurring. AD strips were also inserted into packages and no color change noted. Thus they decided that neither the package, nor the exhibition conditions was causing hydrolysis of the acetate groups. They did find adsorbed camphor in a package containing cellulose nitrate, so scavenging of plasticizers might be an issue. Thus, they think that their environmental conditions are generally good and that the passé-partout packages are not the issue. They are not sure what caused the observed deterioration; whether it was mechanical damage caused by temperature changes, vibration during shipping, etc. and are continuing to look into this. They are also planning to begin looking at the ink and paints to better understand the complete nature of the cels.
For more information on this project see the Getty Newsletter:
http://www.getty.edu/conservation/publications_resources/newsletters/29_1/animation.html
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AIC Blog Archives: Conservators Converse
Former Blog of the American Institute for Conservation