I have observed that people here use (and sell) Acetic acid ( few drops/liter as the stop bath )to get rid of the slimyness on paper, due to developer or fixer so they can reduce the washing timings. Then I tried the same at my place, and it does remove all the slimynes from the paper in really few seconds. somebody aware of this weired thing? Does this Acetic acid (the one you get here in Bombay,India, is labled as "not for medical use") cause any problems over a span of time? Please help Shreepad

-- Shreepad (shreepadjoglekar@usa.net), August 18, 1999

Answers

Acetic acid (or citric acid which has the advantage of not producing as unpleasant a smell as acetic acid) as a stop bath serves two purposes:

1) The developer is highly alkaline, and its action is stopped fairly rapidly when the print is soaked in the stop bath. This effect is only important when you develop your prints by inspection, which is not good practice for ordinary b&w prints, but necessary with lith printing.

2) Neutralising - or rather acidifying - the print helps to keep the fixer acidic (which it must be to be effective). If the fixer must neutralise the alkaline remains of the developer, it is quickly exhausted.

The slimyness you mention comes from alkalinity. Usually, 15 seconds should be enough to neutralise the print provided the stop bath is strong enough. (I can look up the recommendations for an acetic-acid stop bath strength if you wish. I routinely use citric acid, so I don't remember the concentration.)

To my knowledge, there is absolutely no point in using acetic acid (or any other acid for that matter) after the fixer. Quite the contrary! Hypo eliminators are usually alkaline. You can't use an acid as a wash aid. That is the only threat to archival permanence I would see.

I would guess that your medical-use acetic acid contains some kind of denaturant. Acetic acid and ethanol suitable for use in vinegar and drinks, resp., are more expensive in many countries because of special taxes. The denaturants taste so bad that no one will want to taste it. Thus, you need not pay the taxes for denaturated acetic acid and ethanol. I would not expect any trouble from a denaturant in a stop bath, because it should be washed away with the rest of the chemistry.

-- Thomas Wollstein (thomas_wollstein@web.de), August 18, 1999.

A typical stop bath can be made by diluting 28% acetic acid 1:20 with water. Kodak indicator stop bath is similar, but with an indicator that changes from yellow to purple when the stop bath is exhausted. Some photographers use diluted acetic acid, and check it for exhaustion by feeling it for slimyness.

-- jim jones (jjones@greenhills.net), August 26, 1999.