Well, we could try going without it. No, really. Framers survived quite well for centuries before ATG was developed. Sure, it's handy, and it's cheaper than some other tapes. But essential? Nope.
For sticking mats together we could use tapes such as double sided 3M #665 tape or, for archival uses, 3M #415. Both are easy to use, won't migrate, and cost just a little more than ATG when bought in quantity. Another mat-sticking alternative would be frame glue -- just run a bead of it around the perimeter of the opening, and let it dry under weight for a minute or two. Or, for archival framing, starch paste could work the same way.
For holding dustcover paper to frames, frame glue works. It's not as quick & easy, but it makes a better bond. And later, when the frame is disassembled, dry glue is easier to remove than ATG goo. Double-sided tapes would be better than ATG for the purpose, too.
As usual, 3M has done a remarkable marketing job on us. Yes, I use ATG too. Love the stuff.
About "acid-free" ATG: I'm wondering what is the purpose of making acid-free ATG? Whatever acid content may be in regular ATG should be defeated by the alkaline buffers in nearly all matboards, shouldn't it? Surely, 3M and other responsible makers would not suggest that such a pressure sensitive product is suitable for archival mounting. No matter how "acid-free" ATG is, it (and all other pressure sensitive adhesives) will never be suitable for direct contact with any items to be conservation/preservation framed.
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James Miller,PPFA-CPF; PPFA Certification Board Member; FACTS/GAFP Committee Member