What is a stop bath?
The stop bath is really a step in the development process, both in film and paper development. It halts the action of the developer by lowering the PH of the residual developer on the film below the working threshold. When the PH drops below a certain level the developer stops working. Most people use acetic acid for their stop bath. You can use water if you wish, but it is no where near as effective (I think that the PH has to go below 8 for the development to stop, water has a PH of 7, and acetic acid is something like 3 or 4). You can stop the development in an acid stop within 30 seconds, but a water stop bath requires several minutes. Acetic acid can be purchased in two concentrations, 28% and 98% (glacial). Glacial is cheaper, but rather dangerous. A pint of 28% will last you thousands of rolls of film, or prints (Black&White, for color it will only last for hundreds of rolls or prints).
