Homemade Stop Bath Recipe

Donald Qualls · Jul 6, 2023

RalphLambrecht said:
You can take acidic acid(white vinegar) or if you are sensitive to the smell take citric acid(Vitamin C)instead.

I think you meant acetic acid -- this is what's in white vinegar and commercial indicator stop bath. If you value easy over cheap, you can buy the biggest jug of the cheapest brand of white vinegar at the grocery store and dilute two parts vinegar to five parts water to get the desired 2% strength.

Vitamin C, however, is NOT citric acid -- it's ascorbic acid, and is itself a developing agent; not a good choice for stop bath (if it gets alkaline enough from carry-over, it will continue to develop your film instead of stopping it). Citric acid is sold as such in the canning section of larger supermarkets; that's what you want. Failing that, you can dilute lemon juice 1+2 with water and get a usable solution (but probably best to give a water rinse between stop and fixer to avoid carrying over sugars and organics into the fixer).

Xylo · Jul 6, 2023

You can also get citric acid from ecological cleaning supplies shops.
Maybe using Oxalic Acid (I think it's sold under the name Lemon Salt at the drugstore) would be another option?

MattKing · Jul 6, 2023

Home brewers also use citric acid.

john_s · Jul 6, 2023

Citric acid is in the baking section at my local supermarket.

koraks · Jul 7, 2023

Xylo said:
Maybe using Oxalic Acid (I think it's sold under the name Lemon Salt at the drugstore) would be another option?

Probably, but why pick something unnecessarily expensive? Btw, I'd expect 'Lemon salt' to be either citric acid or something like sodium citrate. There's no oxalic acid in lemons. Maybe 'rhubarb salt' or 'sorrel salt'

lamerko · Jul 7, 2023

Some commercial products such as Ilford Ilfostop are actually a solution of citric acid (in combination with some other accompanying but not critical chemicals). One liter of concentrate costs 36 euros, while 1 kg of citric acid costs 7 euros.

Don_ih · Jul 7, 2023

If you have nothing, you do probably already have vinegar. You can get a bit more life out of stop for paper by dipping the print in a tray of water just before putting it in the stop. You may or may not find that important since there would be no indicator in a non-commercial vinegar or citric acid stop.
Film stop use once and pour down the drain.

Donald Qualls · Jul 7, 2023

Xylo said:
Oxalic Acid (I think it's sold under the name Lemon Salt at the drugstore)

Oxalic acid wouldn't be sold for human consumption anyway -- as other have suggested, "lemon salt" is probably citric acid (or salt with some citric acid in it). Oxalic acid is what makes rhubarb leaves toxic, and long term consumption even of sub-acute doses will contribute to kidney stones. The amount in the rhubarb stems that we usually eat is low enough not to be harmful if it's only eaten in season...

Xylo · Jul 7, 2023

Donald Qualls said:
Oxalic acid is what makes rhubarb leaves toxic

And it can make a very good insecticide when made into a tea. But like you said, poisonous like heck.

I'm just thinking about what could be used other than citric acid and vinegar...
There is Kodak SB-3 and SB-4 that use Potassium Chrome Alum...
And there is a formula for a Sodium Bisulfate stop...
But none of those are really things that are easy to come by or cheap.

john_s · Jul 7, 2023

A weak solution of Sodium Metabisulphite makes an effective stop, but it smells of SO2 so is most suitable in a Nova vertical slot processor (small surface area). It smells less if its pH is lifted a bit with NaOH to about pH5 or pH5.5.

koraks · Jul 8, 2023

Xylo said:
There is Kodak SB-3 and SB-4 that use Potassium Chrome Alum...

This was likely combined with an acid, and the acid was the actual stop. The alum is a hardener and it needs an acid environment to be effective. So it's a two birds with one stone situation. The alum is not the stop, though.

Xylo · Jul 8, 2023

koraks said:
This was likely combined with an acid, and the acid was the actual stop. The alum is a hardener and it needs an acid environment to be effective. So it's a two birds with one stone situation. The alum is not the stop, though.

Like you said, it's mostly a hardening bath for tropical development. But for some reason Kodak put it in the stop bath category... It's probably one of those old formulas I got from somewhere. It also doesn't come with much information other than the mixing and the indication that it takes up to 3 minutes to fully harden the emulsion. It also says that if you use DK-15 Tropical Developer, you must rinse for no more than 1 second before using the "stop bath".
The way I think it must have worked is that by rapidly hardening the gelatin you prevent new developer from reaching the silver and thus stop development through developer exhaustion... but that's just an idea.

And considering modern films and all, it's probably a completely forgotten thing by now.

titrisol · Jul 8, 2023

You can buy an indicator called Bromocresol Green, at a 0.04% solution.
Add a drop of that to you stop bath and it will act jus like Kodak's, changing to blue (dark under safelight) at pH 5.6

koraks · Jul 9, 2023

Xylo said:
The way I think it must have worked is that by rapidly hardening the gelatin you prevent new developer from reaching the silver and thus stop development through developer exhaustion... but that's just an idea.

It doesn't work that way. Gelatin hardening ist not a binary variable where all of a sudden it's fully hardened and impermeable. And like I said, potassium alum won't harden gelatin unless the solution is acidic to begin with. So if that alum mixture is acidic, it'll be the acid that stops development. The hardening is unrelated to the stop action.

Xylo · Jul 10, 2023

koraks said:
And like I said, potassium alum won't harden gelatin unless the solution is acidic to begin with.

Since they said to combine it with a tropical developer, I wonder if those aren't a bit acidic to begin with? An alkaline developer would soften an already soft emulsion when processed at a high temperature. Having a slightly acidic developer would help with that... and it would explain the potassium alum.
But if that's not the case, I really don't know why they gave this bath the SB name as most of their hardeners get the F designation as they are combined with the fixers category...

koraks · Jul 10, 2023

Xylo said:
Since they said to combine it with a tropical developer, I wonder if those aren't a bit acidic to begin with?

Pretty much the only developing agent that's active at acidic pH is amidol, and that has historically been used extremely rarely for film at all. So no, the acid would really have been part of the stop bath formula. Which, again, would be crucial in making it a stop bath to begin with.

Xylo said:
why they gave this bath the SB name

Apparently because they emphasized the stop function over the hardening function, and wanted to distinguish it from the other hardeners which were perhaps intended to be used after fixing. Or, more prosaically - they had to call it something.

Xylo · Jul 10, 2023

koraks said:
Or, more prosaically - they had to call it something

Though I must admit that Kodak naming conventions are not always logical... I guess that the H key on their typewriter was broken when they settled on the name
Or they just called it a stop bath because it comes after developer and they didn't want to re-design their order forms to add a category... I just guess that we'll never know.

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