Is stop neccesary with "one shot" film deveoping?

**John Kasaian** · 12-Nov-2007, 00:27

This might take the prize for dumb questions but...
I use one shot chemistry in my processor when developing film, so is a stop bath, or a water stop neccesary or even desireable? IIRC the reason for a stop bath is to prevent the fixer from going south on you from being contaminated by residual developer, but as I'm not reusing the fixer since the processor only requires a small amount of chemicals I prefer to use the "one shot" approach rather than risk exhausting the fixer, so....? or is the residual developer enough to have an effect on the fixer and that would be all the more reason to use a stop?

**Alan Davenport** · 12-Nov-2007, 00:44

Developers and fixers have different pH; the reason for an acid stop bath is (as you know) to prevent the alkaline developer from contaminating the acid fixer. Going directly from the developer to the fixer creates the same problem. Of course, if you're using sufficient fixer it won't be a problem, but you will waste some fixer. I would recommend using at least a water rinse between the dev and fix, simply to ensure that your fixer doesn't start the job already reduced in effectiveness. A water rinse is almost as effective as an acid stop bath, at halting developer action in the film.

**Mick Fagan** · 12-Nov-2007, 00:45

I don't know what kind of processor you are using, but in the commercial world of roller transport (RT) machines, none that I have ever seen have a stop bath for any material, be that film, paper, or Duratrans.

With most RT units, the exit rollers of each bath act as a squeegee. I assume you are not putting film through an RT unit, but you may be.

Regardless of that, if your processing is also one time use for fixer, then I fail to see a need for a stop or wash bath as well. Especially if your film is coming out fully fixed.

Mick.

**Michael Gudzinowicz** · 12-Nov-2007, 05:56

An acid stop partially inactivates developing agents by lowering the pH into a range where the agents are less active, and by dilution. In the emulsion, the rate limiting step is diffusion so stop times are on the order of 30 sec to 1 min.

If the stop is eliminated with used acid fixers, the soluble silver in the fixer will be reduced in the emulsion and at the interface, causing some general fogging and dichroic fog on the surface.

If the stop is eliminated with alkaline fixers, reduction of dissolved silver continues until the developing agent is diluted whether the fixer has been used or not. In the latter case, the dissolution of silver halide crystals provides the silver. With staining developers, one will also get a non-specific stain (fog). BTW, alkaline fixers only speed the first phase of fixer removal - not tightly bound complexes (EKC research).

The details of developer-stop-fixer methodology were worked out over the past century with investments of millions of dollars. If you want to save 30 sec, quality is good enough, and you can tolerate an occasional disaster, then not using a stop is your call.

**PViapiano** · 12-Nov-2007, 09:01

Just a note...I think the label of Formulary T4 fixer states that a stop is not necessary with that particular fixer.

I personally always use a water stop for film and Kodak Indicator Stop for prints.

**rippo** · 12-Nov-2007, 10:41

why not use an alkaline fixer then? there's a recipe in both the Film Developing Cookbook and the Darkroom Cookbook. sodium thio, sodium sulfite, sodium metaborate. apparently washes out of film faster than normal acidic fixers as well. never used it myself, as i've had no need.

**Ron Marshall** · 12-Nov-2007, 11:00

I use TF4 without a stop bath; I wash five times with continuous agitation for ten seconds each after the developer. I reuse the fixer, but run a clearing test before each session.

**rippo** · 12-Nov-2007, 11:08

Ron: i thought the point was that John wanted to avoid the stop-bath stage altogether. i use a water stop bath all the time...quit using acid baths after my first bottle ran out, a long time ago. no point to it, just a way to spend more money!

if the developer is alkaline, and the fixer is alkaline, and the fixer doesn't need to be reused...seems like a stop bath (water or otherwise) could be eliminated.