I reuse stop bath few times. I just pour it back into a bottle labeled "stop working" (funny name, I know). I discard it when it starts to change color. I do this for convenience. It works and I see no need to throw it away after session use.
The problem with indicator stopbath is that people only discard it when it starts to turn purple. The indicator uses bromcresol purple which changes from yellow at pH 5.2 or lower to purple at pH 6.8. Most people do not notice a color change until the pH reaches 6.0. Such a solution is really not useful in stopping development rapidly. A better test is to smell the bath. If it still smells strongly of vinegar then it is still good.
Last edited by Gerald C Koch; 10-25-2012 at 12:07 AM. Click to view previous post history.
A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.