White precipitant in sodium sulphite HCA bath, will it decrease activity?

[Simonh82]

When printing I use a plain sodium sulphite bath for HCA, at 20g per litre. Soon after mixing I get a white precipitant, of what I guess is calcium carbonate, coming out of solution.

Is this anything to be concerned about? Will it decrease the effectiveness of the sodium sulphite as a HCA?

The bath is mixed with plain London tap water.

 

[Ian Grant]

The precipitate can dry into the emulsion, it'll wipe of during washing. It would be better to use de-ionised water for the HCA bath, a jug filter is sufficient.

Ian

 

[Simonh82]

My prints all get a thorough wash after the HCA and I've seen no evidence of white residue. I was really wondering if the precipitant would actually affect the working properties of the bath.

I am careful to keep my fixing times to a minimum (60 seconds in 1+3 strength fixer) and I wash well for half an hour but my fix/wash regime is based on an effective HCA bath.

If the precipitant is nothing to worry about I'm happy to continue as is. For the moment a water filter is just one more thing I have neither the space nor money for.

 

[jochen]

Hello,
the calcium ions of ordinary tap water form calciumsulfite together with sodiumsulfite which is rather poor soluble. Commercially HCA contains EDTA-Na4 as a complexing agent for hard water. If you have access to the complexing agent you can add about 1 g to one liter and you can use tap water.

 

[paul_c5x4]

Something like a Britas jug doesn't take up much space and there are cheaper alternatives available in most countries.

 

[Xmas]

Boil faucet water, mix HCA, filter 24 hours later. The precipitate gets on my prints... Think the Kodak stuff has a sequestering agent - still filter.

 

[Gerald C Koch]

There should be a formula for a HCA substitute on APUG. Check the archives. Lowering the pH of the sodium sulfite solution by the addition of either a small amount of sodium bisulfite or citric acid should get rid of the problem. Citric acid will also chelate calcium ions.

 

[Simonh82]

Thank you, I have citric acid. I'll give it a go. Do you know how much citric acid per litre?

 

[Gerald C Koch]

I would add 2 g for 20 g of sulfite.

 

[Xmas]

(there was a url link here which no longer exists)

 

[john_s]

Kodak HCA also has some (meta)bisulphite which lowers the pH to a level that's supposed to be optimal for its operation.

I don't know, but maybe that would stop the precipitate.

 

[jochen]

Hello,
I think Kodak HCA besides EDTANa4 as a sequestering agent also contains sodiumcitrate as a buffering and chelating agent for calcium ions.

 

[Simonh82]

Just reviving this thread as I have progressed somewhat since I originally posted. Thanks again to everyone who has contributed so far.

Along side the plain sodium sulphite which I have been using I've also ordered some sodium metabisulphite and some sodium citrate. EDTA Na4 seems harder to come by. EDTA Na2 is cheap and easy to obtain but EDTA Na4 is quite a lot more expensive for a much smaller amount. Can the two be used interchangeably, or with modification to the amount used?

 

[Gerald C Koch]

The difference between the two EDTA salts is the pH of the solution that they produce. Since you are already going to use bisulfite either salt can be used.

The white precipitate mentioned is calcium sulfite.

 

[Simonh82]

Thank you. I'll grab some EDTA Na2. I presume that if I thoroughly mix the powders in the appropriate ratio, based in the formulas in the linked threads, then I can just weigh out the correct amount of this mixture and dissolve directly into warm water to make a working solution? I'd prefer not to have stock solutions hanging around. Equally, nor would I like to weigh out tiny quantities of each individual chemical each time I print.

 

[Gerald C Koch]

The amounts of the chemicals are not that critical for a washing aid. This is a solution that can be made up using spoon measure.

 

[Simonh82]

Just thought I would report back on this one for anyone looking in the future. I acquired the four chemicals mentioned in Wolfgang Moersch's post in (there was a url link here which no longer exists), except I used EDTA Na2 instead of EDTA Na4 and Sodium Metabisulfite instead of Sodium Bisulfite. I've mixed them in the proportions listed in his formula and can now report a crystal clear HCA bath.

EDTA2Na 12g
Sodium sulfite 200g
Sodium metabisulfite 6g
Sodium citrate 4g

I've chosen to mix the chemicals dry and then use a scoop which I've marked up with the quantity of dry powder needed for 1L, 2L and 3L of working solutions, based around 20g/L of Sodium Sulphite.

Used in conjunction with my newly acquired Nova archival washer, I'm pretty confident that I have a good archival wash process set up for FB paper, but I will be getting some retained hypo check solution with my next order to confirm this. Does anyone know what the shelf life of HT-2 solution is? I can't imagine that I will get through a lot of it, given how infrequently I actually manage to set up my temporary darkroom.