A-D (acid-detecting) strips are acid-base indicator papers that turn colors in the presence of increasing amounts of acidic vapors, in this case from acetic acid from the chemical decay of an acetate film base. Often acetic acid has a vinegary smell, but the strips provide a more accurate and safer method of evaluating acetate deterioration than sniffing!
- Remove the film from the box. We will not test inside the box in order to avoid inaccurate results based on old, reused boxes (which we are planning to discard anyway) and in order to create a closed, confined space in which the strip will test for acidic vapors created by the deterioration of the film.
- Place a single roll of film and one A-D strip inside a plastic bag. Be sure the strip does not slide inside the rolled film because the strip must be exposed to atmosphere within the enclosed space, but it is okay (even preferred) to put the strip against the edge of the film between flanges of the roll (image shows preferred placement of strips but this might not be possible with many of our film)
- Seal the bag with some air inside it.
- Tape the relevant information from the box to the bag.
- Leave the strip with the film for at least 24 hours (exposure for a few days is preferred). At the end of the exposure period, if you can see through the sealed bag that the color change on the strip is not uniform, then the color change process may not be complete and you should leave it for a while longer.
IMPORTANT: After opening a package, please try to use all the A-D strips. If you can not, then please seal the unused strips inside the resealable polyethylene bag and within the outer bag as soon as possible.
When you are ready to catalog the film,
- Enter basic information into a new record in the database.
- When you open the bag, remove the A-D strip first.
- Compare the strip’s color to the color bands on the pencil. Exact matches will not always happen. Even though only 4 levels (0-3) appear on the pencil, think in terms of 7 possible values: 0, 0.5, 1.0, 1.5, 2.0. 2.5, or 3.0 If the strip’s color is close to one of the bands but not quite there, go ahead and take the number that the color seems similar to. If the strip’s color seems to fall between two color bands, then assign it a value halfway between the numbers.
- Record the number in the “A-D Strip Level” field in the database.
Worried because the A-D strip number seems to contradict your own inspection of the film? Don’t be!
You see clear signs of deterioration (channeling, for example) but the A-D strip value seems low? The acidity can evaporate from film over time.
When you examine the film base, you believe it is polyester, yet the A-D strip gives a value? Polyester-based films can absorb acid vapors from deteriorating acetate-based neighbors or from reused boxes that absorbed it from earlier contents.