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Old 1st April 2021, 11:47 AM
Nat Polton Nat Polton is offline
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Default Bromocresol purple Stop Bath Indicator.

I have just found some Bromocresol purple.
It is used to make the indicator in acetic acid stop baths.
I bought it many years ago for this purpose but never got round to using it.
I also have some glacial acetic acid, which I do not like having around the house. Rather than throw it away I intend to use it up for stop baths.

The Bromocresol purple is mixed up as a separate solution and added to the stop bath and changes from yellow tint to purple when the stop bath is exhausted.
The formula was in one of the many photography books I gave away when photography was put on the back shelf for a good few years.

Does anyone know the formula to mix up the Bromo.purple. indicator solution?

Cheers.
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Old 1st April 2021, 07:55 PM
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Flexing my google mojo... From The Darkroom Cookbook:
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ID:	4138

My copy also includes the warning to always use cold water for the hyrdoxide and add it very slowly - and if it starts to boil, leave the room - do not breath the fumes... Seems like the warm weather has come along just in time to do this outside!

Last edited by Bob; 1st April 2021 at 08:04 PM.
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Old 2nd April 2021, 08:55 AM
Nat Polton Nat Polton is offline
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Thank you Bob.
I shall give it a go soon.

Cheers.
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Old 2nd April 2021, 12:19 PM
Terry S Terry S is offline
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Making up more of my own mixes, I looked into making the colour changing stop bath, but the price of any Bromocresol purple that I could find, made it uneconomical. It's one of the few things worth buying, and is worth it's price, especially as it lasts for so long.

Terry S
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Old 2nd April 2021, 01:50 PM
Nat Polton Nat Polton is offline
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Terry
I have just frightened myself by finding some bromocresol purple on a chemical web site.
For an industrial supplier to list it for sale in quantities starting from 5g gives you an idea of the ridiculous price being asked.
I bought my small amount long before the days of the internet, when chemicals were difficult to find but reasonably priced.
Cheers.
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Old 2nd April 2021, 05:39 PM
EdmundH EdmundH is offline
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Quote:
Originally Posted by Nat Polton View Post
Terry
I have just frightened myself by finding some bromocresol purple on a chemical web site.
For an industrial supplier to list it for sale in quantities starting from 5g gives you an idea of the ridiculous price being asked.
I bought my small amount long before the days of the internet, when chemicals were difficult to find but reasonably priced.
Cheers.
I also looked up the price of this stuff. I think I'll continue to guess when my acetic stop bath is depleted!
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Old 3rd April 2021, 06:44 AM
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Ian Marsh Ian Marsh is offline
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I also looked up the price of this stuff. I think I'll continue to guess when my acetic stop bath is depleted!
Or buy some Ph test strips.
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