I'm not really into developing photos but since I have photogrammetry & photo interpretation subjects at school, I was required to develop a photo and I really liked it. Unfortunately, the photo developing exercise wasn't much coz the developing, stop bath, & fixing solutions were already mixed by the lab technician and I'm wondering, what are the these basic chemical in photo processing? Thank you for your answers. I would really appreciate it!

-- John Francis Haygood (jfaah@edsamail.com.ph), February 10, 2001

Answers

I have an article on mixing developers that details developer components and what each one does. You will find it here:

http://unblinkingeye.com/Articles/Developers/developers.html

The active ingredient in fix is either sodium thiosulfate or ammonium thiosulfate. In addition, fix usually contains sodium sulfite, acetic acid, boric acid, and potassium alum. Stop is usually a 3% solution of acetic acid.

-- Ed Buffaloe (edb@unblinkingeye.com), February 10, 2001.

Stop is about 1.5% acetic acid. Normal vinegar is about 3% acetic acid.

-- Terry Carraway (TCarraway@compuserve.com), February 11, 2001.

John, in case your question is more basic (plus, Ed's stuff shows up in really tiny type on my system), the tech is more than likely just making a commercial mix. For example, the developer is probably from Kodak or Ilford, etc. It's probably either a plastic-lined bag containing a powder or a plastic botttle of concentrate; either is mixed into a certain quantity of water (say 1-gal) at a certain temp (maybe room temp for the liquid mixes). Ditto for fixer.

BTW, developers ususally need to be alkaline (ie, pH higher than 7) to work. The stop bath halts development by dropping the pH.

PS, at the bottom of the question page is a list of archived questions in categories. I see there is a category for both chemistry and developer; you might want to spend some time browsing through there.

-- Plutoo (bcarriel@cpicorp.com), February 14, 2001.