No milky wash water

[ColinRH]

I’ve been making salt prints for some 10 years so have a reasonable handle on the process. For the past 18 months I changed from initial plain water washes to salt water washes. When I washed with plain water I found the tell-tale milky water effect, however with the salt water there is never any milkiness in the water. When making a quick test, yesterday I washed a print in ordinary water and there was the milky effect again.

Can anyone suggest why there is no milkiness with salt water?

Just curious really.

 

[nmp]

The only thing I can think of is the difference in the kinetics of silver chloride formation. In case of tap water, since the amount of dissolved salt is lower, the majority of silver nitrate has a chance to first get dissolved away from the paper and then combine with various ions in the tap water making milky precipitates. For salt-water rinsing, due to higher concentration of available ions, most of the reaction probably happens close to the surface or inside the paper forming larger and heavier particles that can't escape out - so no milk for you!

This would mean that the fixer will have to work harder trying to remove this additional silver chloride in the paper. What I do to counter this is to first rinse with distilled water which simply dissolves the silver nitrate and carries most of it out. Then follow by either tap or salt water to finish the job of converting the rest of the nitrate. Then fixer. I implemented this when working with Centennial POP where I was trying to minimize time in fixer to reduce loss of density due to bleaching that occurs while fixing.

That's my theory, anyway...

:Niranjan

 

[pentaxuser]

Colin How much salt did you need to put in and was this ordinary table salt?

Thanks
pentaxuser

 

[koraks]

I can't explain this; perhaps @nmp is right in his hypothesis, and maybe it's something else. I can't remember for sure if I've seen the same effect, or (which I think was the case in my testing) that adding some citric acid to the wash water prevented the milkiness. Which I assume would be due to the chelating action of the citric acid, which prevents any silver chloride from bunching together, forming a suspension instead of remaining more distributed and locked to citric acid molecules. I just can't remember if plain salt had the same effect when I did this. What I did remember is that adding salt did not seem to improve anything about the processing. The wash didn't seem to be more effective or help against fog occurring later on in the process. Keeping the highlights perfectly clear from any fogging is the single most challenging part of salt prints in my experience - and it's an issue easily overlooked especially if the print borders aren't masked.

 

[ColinRH]

Thanks nmp, I’m no chemist, of course, otherwise I wouldn’t be asking, but your explanation just might be the answer except, see below.

Pentaxuser; for this wash cycle in the process I use 15g of household salt to 2lt tap water.

Koraks; I think you may well have the answer with the addition of citric acid. This is something I do, so as to get the water just into the acid side of neutral.

I had to go back to Christopher James Book where I started using salt; I hope he’ll not complain at me copying this part.

‘ Salt Wash Bath - This first bath in the processing sequence consists of a slightly acidic salt bath whose purpose is to precipitate the free (or excess) silver by producing silver chloride. If you have no salt in this bath you will not be removing the free silver and this will create problems with toning, as the gold will not adhere to the silver unless the free silver nitrate has been eliminated. Following your exposure, immerse your print in this bath of salted water that has been made slightly acidic, lowering its pH, with the addition of citric acid.

• 10 g citric acid• 30 g kosher salt • 1000 ml distilled water

Immerse your print in this solution under low to moderate light, and agitate slowly for about 5 minute’

2-3 washes in clean water follow; followed by a further 15 minute wash in fresh water - not something that I have been doing (oh dear!) then fix.

Thanks for your help, I should have made my own investigation before shouting out! I still don’t understand the reasoning but I seem to be on the right track.

 

[nmp]

As far as I know (I could be wrong, though) citric acid is not a chelator for silver halide (like sodium thiosulfate is) as it is for iron. And silver citrate is a sparingly soluble salt just like the halides.

Colin:

Did/do you put citric acid in both your plain water and salt water baths? Would you observe the same behavior if no citric acid is used?

One way to check my hypothesis is dilute the salt solution successively to see if that starts producing milky precipitates at lower concentrations.


:Niranjan.

 

[koraks]

You might very well be right @nmp. It was the best guess I could come up with.

 

[ColinRH]

I ended my initial post ended with the words “Just curious really.” - having read the above and again the James piece I am now concerned or even in a bit of a panic. I am just coming to the end of a 25 print project and now wonder if all the prints are badly compromised. My washes consisted of 4 x 1m 30 sec washes in the citric acid/salt water; does that mean that all the excess silver and salt are locked in the paper and unlikely to be released?

My only possible saviour might be that instead of giving just 1 minute of 10% hypo as James suggests, all my prints have had 2 x 3 minute fixes in 10% hypo., then sodium sulfite and full wash.

Might that go some way in nullifying the salt wash predicament I find myself in? Or have I got a full re-print to do?

 

[nmp]

I ended my initial post ended with the words “Just curious really.” - having read the above and again the James piece I am now concerned or even in a bit of a panic. I am just coming to the end of a 25 print project and now wonder if all the prints are badly compromised. My washes consisted of 4 x 1m 30 sec washes in the citric acid/salt water; does that mean that all the excess silver and salt are locked in the paper and unlikely to be released?

My only possible saviour might be that instead of giving just 1 minute of 10% hypo as James suggests, all my prints have had 2 x 3 minute fixes in 10% hypo., then sodium sulfite and full wash.

Might that go some way in nullifying the salt wash predicament I find myself in? Or have I got a full re-print to do?

Sorry, Colin....didn't mean to panic you with my crazy conjecture. If you think you might have inadequate fixing and some silver salt left over in the paper, you can check by putting a drop of selenium toner (if you have some) on the border - if it stains you have un-reduced silver present in the paper. Otherwise you are fine, which most likely you are.

:Niranjan.

 

[koraks]

To a larger extent, a suboptimal initial wash will be compensated for by a thorough fix. I personally prefer dilute rapid fixer (1+20 or so for 5 minutes) over plain hypo as the latter seems very slow and difficult to take to completion. The thinner the paper, the easier it is to get the wash and fix to be effective. I'd be somewhat wary of the 2x3 minute fix in plain hypo; I think 2x5 minutes would be the minimum for a really thorough fix in plain hypo.
Do you mask the borders? This makes it so much easier to see if your processing is good enough!

 

[ColinRH]

Thank you both for your input. I do mask the borders so I shall test for silver leftovers with KRST which I have, on one of the plentiful waste prints.
If there is silver leftover I guess further fixing might do the job. Thanks again.

 

[koraks]

If your borders remain clean even after a few weeks and/or after exposure to UV light (after processing of course!) all is well.
I'm not sure if selenium toner will stain unclear whites very well; sepia toner for sure would.

 

[kevin klein]

What is the reason for putting the print in salt water?

 

[Sirius Glass]

What is the reason for putting the print in salt water?

During World War II the US Navy used ocean water as fixer.

 

[nmp]

What is the reason for putting the print in salt water?

Unlike traditional silver gelatin, salt print "emulsion" contains excess silver nitrate (which is what makes it a print-out process.) Before fixing the image using sodium thiosulfate, this silver nitrate has to be removed completely or converted to a silver halide. This is because silver nitrate would react with thiosulfate to form silver sulfide that will cause stains on the paper. So before fixing, the print has to be treated with salt water or even just plain tap water so the fixer does the fixing but not staining.

:Niranjan.

 

[ColinRH]

Just to repeat – I am not a chemist, obviously!

From what you say Niranjan, doesn’t the first fix do the necessary conversion to silver sulfide which is then removed by the fresh second fix? (That is sort of what I thought was the idea for having 2 baths). Or is this where the use of a later salt bath, pre-fix, supposedly does the job?
I’m not getting any obvious stain anywhere but my concern was long term effects from my process using salt baths – which now seem dubious. I have made test pieces of normal coated paper and then put them through varying processes - first washes with acid /without acid, 5 x 10 minute final sloshing trays /full ‘archival’ Nova washing, with/without salt.

Once dry I put spots of neat KRST from the bottle on the papers, left them for 10 minutes then washed them. To varying degrees they all have stains on them, one was very feint but it is still there. I have run out of thiocarbamide for sepia tone.

I know salt prints are notoriously difficult to get right but as this is likely to be a historical project for the long term, as close to archival is where I am aiming. I am binding the final prints into a book so in general, daylight will not get them but internal chemicals might/will.

 

[nmp]

Just to repeat – I am not a chemist, obviously!

From what you say Niranjan, doesn’t the first fix do the necessary conversion to silver sulfide which is then removed by the fresh second fix? (That is sort of what I thought was the idea for having 2 baths). Or is this where the use of a later salt bath, pre-fix, supposedly does the job?
I’m not getting any obvious stain anywhere but my concern was long term effects from my process using salt baths – which now seem dubious. I have made test pieces of normal coated paper and then put them through varying processes - first washes with acid /without acid, 5 x 10 minute final sloshing trays /full ‘archival’ Nova washing, with/without salt.

Once dry I put spots of neat KRST from the bottle on the papers, left them for 10 minutes then washed them. To varying degrees they all have stains on them, one was very feint but it is still there. I have run out of thiocarbamide for sepia tone.

I know salt prints are notoriously difficult to get right but as this is likely to be a historical project for the long term, as close to archival is where I am aiming. I am binding the final prints into a book so in general, daylight will not get them but internal chemicals might/will.

Hi, Colin:

I am not a chemist either but (as a ChemE from long time ago) I pretend...

So we have 2 different issues here.

One is potential silver halide staying on the paper due to inadequate fixing - the result of of which would be print darkening over time as it gets exposed in the ambient. That is what you are dealing with here.

The second issue, related to the question as to why treat the paper with salt water prior to fixing, is if for some reason, the excess silver nitrate is not all removed (or converted to a halide) from the paper before fixing, it will form a stain of silver sulfide by reacting with sodium thiosulfate.

Na2S2O3 + 2AgNO3 --> Ag2S2O3 + NaNO3
Ag2S2O3 + H2O --> AgS + H2SO4

AgS, silver sulfide, is not soluble and sodium thiosulfate can not remove it like it can silver halide. So the stain will stay on the paper permanently. You can easily demonstrate it by taking some fixer and add to it a few drops of silver nitrate solution. Dark precipitates should follow. Incidentally, this is the basis of the residual fixer test - the testing solution contains silver nitrate.

The 2 fixer baths have something to do with complicated multi-step process of thiosulfate/silver halide complexation which ultimately results in a soluble form that can be washed out. Presumably the first bath goes part of the way which then is taken forward to completion by the 2nd fresher bath. It is unrelated to any silver nitrate that might be present.

Regarding testing of fixation with KRST, there is one complicating factor which is it will also darken any free sliver there might be. So you have to make sure there is not a hint of fog where you do the test. In my experiments with Centennial POP, I simply took a strip of bare unexposed paper thru my process without any exposure and then tested it with KRST. The advantage of an indirect sepia toner like sodium sulfide suggested by koraks is it will leave the silver largely alone and react only with the halide. But I think there would still be some form of discoloration so for judging, a good control is necessary for comparison.

Hope you are able to figure it all out...sounds like a great project!

:Niranjan.