Recognizing the 20th Anniversary of IPI’s A-D Strips® – 1995-2015

A-D Strips

“A fantastic little piece of paper” – Jean-Louis Bigourdan, IPI Senior Research Scientist

IPI sells an average of 1,435 packages of A-D Strips® every year. With 250 strips per package, we estimate that over seven million items held in collections around the world have been tested.

Extensive research on film base stability and evaluation of acetate films incubated at various temperatures and moisture content levels determined that acidity generation was the most sensitive and reliable indicator of acetate base decay. This led to the development of A-D Strips, a diagnostic tool for detecting the presence and assessing the extent of vinegar syndrome in acetate film collections.

IPI's goal was to develop an acid detector which would work as an "early warning system" to identify film in the first stages of vinegar syndrome prior to physical changes such as distortion or shrinkage. Research had shown that acetate decay is autocatalytic, meaning that the acidic byproducts of acetate decay accelerate further decay. Acidic vapor can contaminate nearby films in good condition, putting a whole collection at risk. A safe, reliable, and non-destructive tool to detect the early stages of decay was needed so that steps could be taken to remove the deteriorating films and to place them in a colder location while waiting for duplication.

Once exposed to degrading acetate, A-D Strips turn from blue, through shades of green, and finally to yellow as they react to the presence of acidic vapor in a confined space around the film. The more dramatic the color change, the more advanced the film decay. The color changes are then compared to a color scale printed on the reference pencil provided in each package. Although both nitrate and acetate plastics are prone to chemical decomposition, A-D Strips are calibrated for use with acetate film.

A-D Strips have also been used to detect acidic off-gassing in other museum situations, such as inside display cases, testing of mat board with PVA as a binder, textiles with plastic fibers, and the air inside storage containers. In these cases the quantitative color scale doesn’t apply as it does for acetate, but the results can give a sense of the presence of volatile organic acids.

A-D Strips were initially developed to identify degrading materials so that they could be segregated from, and minimize contamination of, other collections materials. Twenty years later the most promising approach is to use A-D Strips to determine the current and prioritized needs of acetate collections in terms of storage conditions. The more advanced acetate degradation is, the colder the storage environment needs to be.

A-D Strip survey results, used in combination with life span predictions at a wide range of temperature and RH conditions, enable collection managers to identify the best-fit environment for their specific situation. This approach is at the core of FilmCare.org.

The development of A-D Strips was made possible by funding from the Division of Preservation and Access of the US National Endowment for the Humanities, the National Archives of Canada, the Canadian Council for Archives, and the National Film Board of Canada.