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

Ray Patrick Cebu, Philippines

-- Ray Patrick (rpeg@yahoo.com), April 14, 1999

Answers

The normal stop bath is indeed acetic acid.

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.

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.

-- Alan Gibson (Alan.Gibson@technologist.com), April 14, 1999.

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.

-- Tony Brent (ajbrent@mich.com), April 14, 1999.

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

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.

Remember, acids into water but not water into acids when you're mixing from strong solutions.

-- John O'Connell (oconnell@siam.org), April 15, 1999.

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).

-- steve (swines@egginc.com), April 16, 1999.

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.

-- Gene (nikonguy@emji.net), April 16, 1999.

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.

-- Ed Buffaloe (edbuffaloe@earthlink.net), April 22, 1999.