Stop bath - another question for the darkroom guys.

[Actor]

Kodak (and others) sells an "indicating stop" solution. It turns blue when the stop solution is used up. This sounds like a litmus test. Does this mean that if the stop is pink at the beginning of your session and blue afterward that at some point your stop bath failed. Or does it turn blue when the bath is still slightly acidic?

[moviemat]

I dont know the answer to your question but I don't use a stop bath. In my experience water is just as good, so i don't know how important it is. I can't see the point of an indicator if you have to predict changing the solution before it actually indicates anything, if you see what i mean.
So if I were you I'd change it quickly once you spot that it's gone blue but don't worry that your film is in peril.

Mat

[Actor]

Stop bath halts development immediately and reduces the amount of washing required. It also prevents contamination of fixer by the developer, so your fixer lasts longer. Without stop bath the developer continues to act during washing. If you were to change your procedure and use stop bath you might find that you need to develop longer to get the same result.

Your comment about having to predict changing the solution before it actually indicates anything reflects my logic exactly. It's the reason I asked.

Anyway, some further research reveals that the indicator is bromothymol violet (that got the spell checker's attention :lol: ) and it can be formulated to change color when the solution is still quite acidic. Mystery solved.

[moviemat]

Glad that's cleared up then. I wish I could be so presice somethimes but I'm just too impatient. I always develop too long as well becasue no matter how many times I shoot and do a DIY development i can never quite beleive it's had enough exposure.

Mat