Indicator stop bath

Truzi · Apr 27, 2013

I've searched and RTFM, and have not found a good answer to this question, only passing references.
Yes, I know many do not use stop bath, but at the moment I do.

So far I've not setup a darkroom, so have only been developing film in daylight tanks. My developing has been so sporadic that I've generally dumped chemicals long before using them up, but that will change soon.

This seems like a stupid question to me as there are no black-lights or otherwise fluorescing chemicals. The only references I've found state that stop bath changes color under safe-light.
Am I correct in assuming the indicating die in the stop bath will change color regardless of how it is viewed? I just want to confirm that I do not need to view it under a safe-light to see an obvious color change.

eddie · Apr 27, 2013

The color change can easily be seen, regardless of the light source. It will turn from a pale yellow to purple.

bdial · Apr 27, 2013

Yes, the color change is apparent in regular light.
As I recall, Kodak indicator stop turns purple, probably easier to see in white light, at least if you're using light colored trays.

kevs · Apr 27, 2013

Hi Truzi,

You don't need a safelight to see the change in colour of an indicator stop bath. It changes from a straw colour to purple.

FWIW I've stored photographic chemicals for years (including stock developers) in airtight plastic pop bottles. Fixers and acid stop-bath won't deteriorate in the same as developers can. But YMMV, of course.

Cheers,
kevs

Herzeleid · Apr 27, 2013

The indicator used is often bromocresol purple at least it is the indicator in Kodak indicator stop bath. You can find samples of its color changing according to ph.

Truzi · Apr 27, 2013

Thanx,

It did seem obvious, but I wanted to make sure. My only darkroom experience (not much) had been in school/public darkrooms, so I've never had to deal with maintaining chemicals until a few years ago when I started developing film in my bathroom. Tech sheets and other instructions are easy to follow, but often assume people already know the very simple things (like how gently to agitate).

I wish the indicator started purple and changed to yellow - I like purple

hgernhardt · Apr 27, 2013

I like purple too. That could also work under safelight. The traditional color (AFAIK) for the stop bath tray is yellow; so starting with purple under red safelight would give you mud if it's good, clear if it's bad. Hm.

PhotoJim · Apr 27, 2013

It's obvious to me when the colour is shifting, even when the safelight is on. It just looks wrong when it starts to go.

AgX · Apr 27, 2013

A tiny strip of indicator paper would do the job with regular stop bath too.

Newt_on_Swings · Apr 28, 2013

I once tried adoramas indicator stop bath, because it's was a bit cheaper but the indicator didn't really work like kodaks. I just got darker but didn't go purple. Which left me guessing. I didn't like that and went back to kodaks.

MattKing · Apr 28, 2013

I think I understand why the OP might have been confused.

The indicator in stop bath changes colour when the stop bath becomes exhausted. That change is easily seen in normal room light. Additionally, it is advantageous if the colour change is easily seen under darkroom safelight. In the case of both the Kodak and Ilford products, the colour change is easily seen under darkroom safelight.

mkillmer · Apr 28, 2013

I use Rollei Citrin Stop batch (RCS). It turns an opaque black in normal light - there is no question when it expires!

cmacd123 · Apr 28, 2013

under the typical OC or 902 safe-light the Ilford or Kodak bath looks clear, and as it turns purple it starts to look black under the yellow light. in white light it goes from yellow to Purple. once it starts to change, time to mix up a fresh trayful.

edcculus · Apr 28, 2013

FWIW, I was curious about this too a while back, so I just set aside a little developer and stop bath and slowly mixed them. The color slowly turned muddy to purple as I added more developer. I suggest you try this simple "experiment". Then you will know exactly what to look for.

Truzi · Apr 28, 2013

edcculus said:
FWIW, I was curious about this too a while back, so I just set aside a little developer and stop bath and slowly mixed them. The color slowly turned muddy to purple as I added more developer. I suggest you try this simple "experiment". Then you will know exactly what to look for.

Great idea, and odd that I didn't think of it myself because that is something I'd normally do. I think I was trying to save the stop, but am certainly not against sacrificing some to learn.
I've about 500ml of 9-month-old D-76 that is forming some weird strings, plus I'll be mixing fresh developer soon and running some test rolls. I'll dump this into some a bit of old 9-month-old stop so I can finally see what it looks like when exhausted.

edcculus · Apr 30, 2013

You really don't even have to sacrifice that much. I took probably 50mL of stop bath and slowly poured in some mixed developer until I saw a change. In my case I'm using Kodak Indicator and it turned purple. Before I did this, I was saving stop bath after printing, but dumping it when developing film. Now that I know this, I dump the stop bath from the container into a beaker. If its turned purple, I dump it. If not, it goes back into the storage container. I don't shoot or print as much as some do, but I've never actually had a batch turn yet.

Indicator stop bath

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