In the early days of photography, emulsions were unhardened or poorly hardened. This led to the formation of bubbles by reaction of carbonate from developer carryover to the acid in the stop bath or acid fixer. The reaction with an acid fixer can take place even with a short rinse of water.

However, first it must be said that the carbon dioxide that is formed is in very tiny amount and it dissolves rapidly in the water of the stop bath, and so when these bubbles were observed, it was usually in a deep tank process where hydrostatic pressure prevented the bubbles from being released until the film or paper approached the surface of the tank and the pressure was reduced.

The result was that the bubbles didn't show up in tray or shallow tank processes, but did sometimes in deep tank photofinishing processes. This was seldom and only seen pre-1960s.

In the 60s, most major film manufacturers switched over to hardeners that allow processing up to 100F for color films and papers and over 68F for B&W films and papers. These new products are not affected by the use of an acid stop bath in any way as far as can be determined, even in deep tanks or at high temperatures (RA color paper with a stop at 100F has no problems with pinholes and the RA and C41 developers are both carbonate based).

The only way I can generate bubbles (not pinholes) is to coat a totally unhardened emulsion at very high gelatin and then use an acid stop. I can see bubbles form before my eyes, and they don't form in the stop, they form in the acid hardener fix and can even form in the wash. They appear more like blisters.

I must add that not all manufacturers use these new modern hardeners, and therefore you might, in extreme cases, see blisters or marks from acid/carbonate interaction in such films.

I have never observed even this, but I warn you of the possibility.

I have used acid stops for film and paper for over 30 years with absolutely no problem, but have had problems of one sort or another with using a water rinse after development.

I will continue to use an acid stop.

PE