Citric Acid Stop Bath

Photo Engineer · Jun 10, 2011

RalphLambrecht said:
The pH does not drop significantly from 3 to 5% (4.75 to 4.64 pH). I think this is too high for a stop bath. I'll get to my books next week and can look up Haist's suggestion again.

Ralph;

See my comments from Haist above.

PE

Gerald C Koch · Jun 10, 2011

RalphLambrecht said:
The pH does not drop significantly from 3 to 5% (4.75 to 4.64 pH). I think this is too high for a stop bath. I'll get to my books next week and can look up Haist's suggestion again.

The actual pH of the stop bath is not that important and a mildly basic stop bath will also work. What is important is the buffer capacity in reducing the alkkalinity caused by the developer in the emulsion. Plain water will work in stopping development by significantly reducing the pH and concentration of developing agents in the emulsion. Some people do not like to use plain water fearing that development is not halted fast enough. However the fact is that whether a stop bath is used or plain water the process kinetics are determined by the rates of diffusion of various species through the emulsion. The only difference between a stop bath and water is diffusion of hydronium ions H3o+ into the emulsion in the first case and neutral water molecules H2o in the second case. I would expect that the charge on the hydronium ions would probably slow their diffusion as compared to neutral molecules such as water. The diffuson rates for the developer species out of the emulsion should be identical in both cases.

The only advantage of using an acidic stop bath over plain water is that the stop bath need not be replaced as often.

wogster · Jun 11, 2011

Gerald C Koch said:
The actual pH of the stop bath is not that important and a mildly basic stop bath will also work. What is important is the buffer capacity in reducing the alkkalinity caused by the developer in the emulsion. Plain water will work in stopping development by significantly reducing the pH and concentration of developing agents in the emulsion. Some people do not like to use plain water fearing that development is not halted fast enough. However the fact is that whether a stop bath is used or plain water the process kinetics are determined by the rates of diffusion of various species through the emulsion. The only difference between a stop bath and water is diffusion of hydronium ions H3o+ into the emulsion in the first case and neutral water molecules H2o in the second case. I would expect that the charge on the hydronium ions would probably slow their diffusion as compared to neutral molecules such as water. The diffuson rates for the developer species out of the emulsion should be identical in both cases.

The only advantage of using an acidic stop bath over plain water is that the stop bath need not be replaced as often.

I think you were doing well, until the last line, I think it should be: The only advantage of using an acidic stop bath over plain water is that the fixer bath need not be replaced as often.

Photo Engineer · Jun 11, 2011

I have found that many people use a water bath for stopping development. Many of the problems reported to me in e-mails and PMs relate to this use. A RUNNING WATER RINSE is needed, not still water if that is what you want to use. Otherwise, the water bath with "season" with developer and that is not good. It also exhausts the fix more rapidly.

PE

georg16nik · Jun 11, 2011

In school they taught us, that we should use acetic acid stop bath and that the distilled water is a photographer's best friend - so I pretty much did that for a few years (on and off) I remember tried citric acid as well - its ok as long as You watch Your pH tester ; )
I wonder if any of You are using electro-activated water (Anolyte pH ~ 5) for stop bath?

G

Gerald C Koch · Jun 11, 2011

wogster said:
I think you were doing well, until the last li.ne, I think it should be: The only advantage of using an acidic stop bath over plain water is that the fixer bath need not be replaced as often.

My post was concerned about what happens in the emulsion. The suport material in FB materials brings in anither consideration. Mason makes two points. First, normal diffusion phenomena operate in the emulsion. Second, diffusion within the swollen emulsion is very rapid. The same cannot be said about a fiber base. I always use a stop bath with FB papers. Your point is well taken in this respect. The amount of carryover with non-fiber materials is very smalll and a fixing bath is usually exhausted by silver and iodide buildup before carryover becomes a problem. PE makes a good point in that when using water as a stop it should be replaced frequently.

nworth · Jun 11, 2011

I use citric acid stop bath with amidol (which I seldom use), but acetic acid for everything else. Citric acid may have some advantages for stain prevention, but that is seldom a problem with ordinary developers. As for pH, I've seen sulfuric acid called for in a rapid film process; I think the idea is to sort of neutralize the developer. Citric should work just fine. One unpleasant experience I have had with citric acid is mold growth; it seems to be an excellent medium for some things.

JS MD · Jun 11, 2011

what's wrong with regular Vinegar?

Ian Grant · Jun 11, 2011

JS MD said:
what's wrong with regular Vinegar?

It stains prints, white vinegar & acetic acid don't. Of course there's a lot of variations in vinegars but the cheapest here in the UK are Malt vinegars and quite brown in colour.

Ian

M. Lointain · Jun 11, 2011

I started using citric acid a few months ago. I always hated the smell of indicator stop. I just sprinkle some citric acid in water (guesstimating the 10g) and away I go. I haven't had any problems so far. I use really strong developer too and everything seems to be getting along just fine.

MattKing · Jun 11, 2011

JS MD said:
what's wrong with regular Vinegar?

Pure white vinegar is fine, as long as it is pure.

It does, however lack an indicator, and it works out to be more expensive than stop-bath, unless you buy it in very large containers, in which case it creates a storage challenge.

Gerald C Koch · Jun 12, 2011

If you use white vinegar to make a stop bath, check the label. Some brands are 5% but others are only 4% acetic acid.

Citric Acid Stop Bath

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