A number of pressure sensitive tape adhesives pass the Photographic Activity Test (PAT). However, materials used for the storage of photographs must both 1) pass the ANSI 9.16 PAT and 2) meet the requirements of the ANSI IT9.2 Filing Enclosures standard. In IT9.2 it states that pressure sensitive tapes or adhesives should not be used on enclosures (or directly on photos, by reference) because of the tapes' long-term aging characteristics and other physical characteristics, in addition to the fact that they may cause fading or staining if they have failed the PAT.
The long-term aging and physical characteristics that make pressure sensitive tapes undesirable for use with photos (and most valuable historic artifacts and documents) include: 1) the tendency to ooze with cold flow of the adhesive over time; 2) the tendency to become difficult to remove during the middle stages of natural aging; 3) the tendency of many to have oily components that migrate out into the adjacent material, causing transparency in those materials during the middle stages of aging; and 4) the tendency to fail during the late stages of natural aging. The PAT does not test for these characteristics-only for interactions with image materials and the gelatin emulsion, i.e., fading or staining.
For the above reasons, pressure sensitive tapes or adhesives, even ones that pass the ANSI IT9.16 PAT, should not be used on valuable historic photographs intended to be kept for generations in a stable and pristine condition. For less valuable photographs, or those requiring only temporary use before being discarded, the use of a tape that passes the PAT is still preferable, because staining or fading will be minimized or nonexistant during the period that the photograph is kept, compared to the use of a tape which does not pass the PAT.
Use of tape to seal paper or plastic enclosures should be carefully evaluated the same way, and again a tape that passes the PAT is desirable, for the reasons stated above. If tape must be used in construction of enclosures, it should not be used near overlapping edges where adhesive cold flow could cause it to ooze onto the photograph stored inside. Also, tape is safer to use on thick papers, boards or plastics where migration of oily components would take a much longer time to reach the photograph, hopefully longer than the enclosure would be needed for use before replacement!
There are a few circumstances where a conservator might consider the use of a pressure sensitive tape that passes the PAT, on or near a valuable photograph: for example, sealing cased objects to their cover glasses; using a double-sided tape to adhere photo corners to a thick album page with plastic cover sheets for housing of photos or paper memorabilia, or for temporary display where traditional hinging is undesirable or unfeasible, if done in a way to minimize the dangers from oozing adhesive and oily components. Less typical circumstances might include: temporarily hinging RC prints for a short duration of display if testing shows that the tape can be removed safely; and replacement of failing (or disfiguring) tape incorporated into an artwork intentionally. There are perhaps some other cases that are even more esoteric. In any of these examples, there might also be alternative options that would not require the use of a pressure sensitive adhesive at all.
None of the above statements is meant in any way to endorse or condemn any particular manufacturer's product, but to elucidate the requirements of photographs and the complexity involved in the evaluation of all adhesives and materials (not just pressure sensitive ones) that one might use in conjunction with photos, whether historically valuable or not. The availability of adhesives formulated to be the least harmful as possible in their class is always desirable in the preservation field even if they may not be used in all traditional conservation applications-people will use tapes, and conservators will have to deal with any problems that might arise as a result.