Life of chems in solution - EDTA and others

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Stephan Goldstein - 29 Oct 2004 12:01 GMT

Since my darkroom use is infrequent, I don't want to mix up
a giant batch of wash aid stock, only to have it oxidize before
I can use it all. So I was thinking of making it up from powder
for one-shot use as needed.

The recipe I have (posted by Richard K some time back, thx!)
calls for sodium sulfite, sodium bisulfite, EDTA tetrasodium,
and sodium citrate. I think for my uses I can leave out the
bisulfite. The quantity of sulfite to make a couple of liters of
working solution is manageable, but the last two ingredients
are more problematic - the recipe calls for 1g/l each for the
*stock* solution, which then gets diluted 1:4 for use.

I don't have a scale with suitable precision, so was thinking
of mixing up a more-concentrated solution and then adding a
few ml as appropriate. Here are my questions:

1. Does anyone know the life of EDTA tetrasodium salt and
sodium citrate in solution?

2. Does anyone know the solubility limits of these two chems
in solution?

3. Can I make up a stock of both in the same bottle, or would
I be better off with separate stocks?

Thx! This group is a great resource.

Steve

BTW, to reply by direct email you'll need to swap the zero and
the letter o that appear in the left-hand part of my address.

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Tom Phillips - 29 Oct 2004 12:22 GMT

> Since my darkroom use is infrequent, I don't want to mix up
> a giant batch of wash aid stock, only to have it oxidize before
[quoted text clipped - 12 lines]
> of mixing up a more-concentrated solution and then adding a
> few ml as appropriate. Here are my questions:

Well, not answering your questions, it is not that difficult
to obtain a scale that weighs out grams. My Ohause balance
beam does 0.10 grams.

But OTOH, KHCA is pretty cherp and comes in liter packages...

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Dan Quinn - 30 Oct 2004 09:59 GMT

RE: sg0ldo1867@yahoo.com (Stephan Goldstein)

The EDTA and citrate are for hard water. I use distilled when
making up hca. I've very hard water.
Using only sulfite your hca will be moderately alkaline. Dan

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Richard Knoppow - 30 Oct 2004 19:30 GMT

> Since my darkroom use is infrequent, I don't want to mix
> up
[quoted text clipped - 43 lines]
> the letter o that appear in the left-hand part of my
> address.

This must be the formula for a wash aid similar to Kodak
Hypo Clearing Agent. The bisulfite is more important than
the sequestering agents. The idea is to buffer the mixture
to neutral pH. Sulfite alone will give you the ion exchange
function, which is the key to the effecgtiveness of the wash
aid and also raise the pH above the isoelectric point of the
gelatin. The buffer sets the pH at the minimum swelling
point of the gelatin. The sequestering agents are there
mostly to prevent deposition of minerals from the water or
from the fixer on the emulsion. If you use the wash aid only
once and rinse the materials before putting them in the wash
aid the sequestering agents are probably superfluous. Sodium
metabisulfite is equivalent in this application to bisulfite
and is easier to obtain.
I have no idea of the life of EDTA or citrate in solution
but suspect that neither is affected much by oxidation.

Signature

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com

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Mike King - 31 Oct 2004 14:57 GMT

Formulas from David Vestal, The Art of Black and White Enlarging, with
credit to Dignan and Zone V, Inc.

Wash aid for prints
3 liters water--I use water from my home filter
80 grams sodium sulfite
WTM 4 liters

Wash aid for film
3 liters water
80 grams sodium sulfite
8 grams sodium bisulfite
WTM 4 liters

The second formula is slightly more acidic and probably safer for films, not
all films are hardened to the same degree. You can probably safely omit the
bisulfite if you use TMax or Delta films.

Note that both formulas are easily divisible by four if you want to make a
liter at a time. Figure capacity at 100 8x10's per gallon/4 liters.

I recently purchased a fair sized lot of KHCA and mix it up as a stock
solution. The stock solution keeps for a very long time and is diluted 1+3
for use. I got it so cheap I have been using it one shot (since a liter of
working solution is only good for about 25 8x10's and I also one-shot it in
my Unicolor Film Drum when souping film).

darkroommike

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> Since my darkroom use is infrequent, I don't want to mix up
> a giant batch of wash aid stock, only to have it oxidize before
[quoted text clipped - 28 lines]
> BTW, to reply by direct email you'll need to swap the zero and
> the letter o that appear in the left-hand part of my address.

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