Acetic acid as stop bath

I understand that acetic acid could be used as a stop bath, should I dillute it or use it purely?

 

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Ray Patrick

Cebu, Philippines

The normal stop bath is indeed acetic acid.

 

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The pure stuff is pretty corrosive: dilute it to about 1+200. The

stuff you buy in photo shops is already diluted about 1+3. Or take

some vinegar, and dilute it something like, I dunno, 1+60.

 

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If you really want to create your own chemistry, I suggest you read

some books about it first. There are many hazards for the unwary.

Yes, straight or "glacial" acetic acid is very irritating and

corrosive. Use caution. If I am using Glacial acetic, I mix about a

capful at most with water to about half fill an 8 x 10 tray. Not

critical. If using 28% acetic acid (common way of selling it) I

believe the dilution is about 1:4 to 1:6. If your prints "sing" or

sizzle when you drop them into the stop bath, it is mixed too strong.

Kodak Indicator Stop Bath changes color when it is exhausted.

Grocery store vinegar is about 3-5% acetic acid, unless my memory is

very faulty.

 

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Kodak's indicator is probably handy, but I'm lazy -- and I used to be

a dyer. I toss it when the acetic odor is gone or weak.

 

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Remember, acids into water but not water into acids when you're mixing

from strong solutions.

Stop bath should be 2% acetic acid. The dilution directions on Kodak

28% acetic acid say "...dilute 6 ounces in 1 gallon of water for a

working solution." What I normally do is add the 16 ounce bottle of

28% to 38 ounces of water and then dilute that "stock solution" at a

ratio of 9 parts water to 1 part stock solution (100ml stock solution

and fill graduate to 1000 ml).

Most films are better off with out a stop bath step after development. The best stop for film is a 30 second rinse of plain water. Many developer manufacturers recommend against using acetic acid for films. For prints, the stop should be used to extend the life of the fixer.

To round this out, I recommend a water rinse followed by a brief bath

in 2% acetic acid. Going direct from the very alkaline developer to

the very acid stop can sometimes cause pinholes. The water bath

prevents this, and the stop bath in turn prevents the fixer from

becoming too alkaline to do its job.