Citrates for salt printing

Hello. Can anyone tell me the difference between using sodium citrate versus potassium citrate in the salting solution? I've read the manuals from both Young and Anderson and find no reference to potassium citrate. Young covers different chlorides but only refers to sodium citrate as an additive.

thanks,
ole squint

Probably very little difference. Wynn White has suggested KCit.

Agree with the above answer... little if any difference, especially if you adjust for the greater mass of the potassium salt compared to the sodium salt in order to keep the molar concentration of citrate constant.

The molar mass of Na Citrate is 258.1 g/mol and that of K Citrate is 306.4. Since 306.4/258.1 = 1.19, you would want to use 1.19 g of the potassium salt for each gram of the sodium salt called for in a recipe.

I suspect Na or K citrate will make somewhat different colors, but not a big difference.

NedL said:

I suspect Na or K citrate will make somewhat different colors, but not a big difference.

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My educated guess is that if there is a difference it would be due to using the same weight of the two different compounds thereby changing the concentration of citrate not because the cations are different.

I am not interested enough to do the experiment though.

fgorga said:

My educated guess is that if there is a difference it would be due to using the same weight of the two different compounds thereby changing the concentration of citrate not because the cations are different.

I am not interested enough to do the experiment though.

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Hi Frank, I'm not either My guess was based on experimenting with chlorides.

In my experience, equal molar concentrations of Cl with sodium, potassium or ammonium cations produce different hues of brown when keeping all else the same. My hypothesis is that the cations affect the absorption into paper/sizing in some minor way. I remember that on most papers I tried, KCl produced a less reddish more purplish and darker brown. Not any dramatic difference though.

I was imagining a change in Cl density after drying, but since I salt papers by floating for a fixed number of minutes, perhaps it could be a change in the total amount of Cl absorbed by the paper too, which would be close to your supposition!

Ned (@NedL),

Interesting result. And yet another alt process rabbit hole to disappear down if we are not careful.

I am trying hard not to go down these rabbit holes, but the scientist in me makes it difficult to resist the urge sometimes. At this point in my life I'm trying to concentrate on making art.

Regards,

fgorga said:

...
I am trying hard not to go down these rabbit holes, but the scientist in me makes it difficult to resist the urge sometimes. At this point in my life I'm trying to concentrate on making art.

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I'm the same ( scientific career/mindset ). I get caught up in testing because I get curious. But now I try to limit the testing to things I'll actually use to make prints! When I get back to salt prints -- soon I hope -- I'll be using materials I've already done extensive testing with

FotoD said:

Probably very little difference. Wynn White has suggested KCit.



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Right. That's what led me to ask the question. Citrates are mentioned as an aside in Young's and Anderson's manuals. Both advise adding 20gm/L. I'm adding the citric acid to the salting solution rather than the silver sensitizer. I've got sodium citrate, so I'll try that before ordering potassium citrate.

Thanks to all

ole-squint said:

Right. That's what led me to ask the question. Citrates are mentioned as an aside in Young's and Anderson's manuals. Both advise adding 20gm/L. I'm adding the citric acid to the salting solution rather than the silver sensitizer. I've got sodium citrate, so I'll try that before ordering potassium citrate.

Thanks to all

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Hold on a second!!!!

You say that you want to add citric acid to the salting solution and then you go on to talk about sodium or potassium citrate.

Citric acid and citrate are not the same thing.

These species are related but have they very different properties.

Citric acid is a tri-protic organic acid, i.e. it has three acidic hydrogens. Citrate is the conjugate base of citric acid. Citrate is citric acid with the three acidic hydrogens removed. Citrate is a tri-anion and is a weak base. Citric acid and citrate react with other materials in very different ways.

In this case, at least part of the reason to include citric acid in the salting solution is to remove (some) of the alkaline carbonate 'buffer' present in many modern papers. Neither of the citrate salts will perform this function.

I note that Wynn's recipe cited above calls for potassium citrate in the salting solution. I don't know who Wynn is nor what his rationale for this addition is.

However, I just went back and re-read Christina's book where she describes Marek's idea of including 50 g /L of citric acid in the salting solution. It is clear from the text that this addition is meant to remove carbonates from the paper.

That said, my practice is to remove the buffer from paper that needs this using dilute (1%) hydrochloric acid (HCl). I soak the paper in the dilute HCl until the bubbling stops (roughly 2 minutes, but it is paper dependent). Then I hang the paper to dry. (Note that I do not wash the paper in plain water before drying.) I then salt the paper separately using just salt.

I do it this way because I also need pre-acidified paper for Pt/Pd printing and this allows me to use the same stock of paper for both processes. Although I must admit that the bulk of my printing (for both salted paper and Pt/Pd) these days is done on paper made for alt processes (HPR or Revere Pt). I need a very good reason to stray these days.

Using a strong acid such as HCl allows one to confirm that the carbonate is completely removed; when the bubbling stops all of the carbonate is gone. With a weak acid such as citric acid, the bubbling is less vigorous and thus harder to observe. Furthermore, you are more likely reach the capacity of the solution for neutralizing the carbonate base without knowing it.

Concentrated HCl is inexpensive and readily available (at least in US). One does have to be careful when handling the concentrated acid (remember to add acid to water, and not the other way round) but it is not particularly dangerous.

All of that said, I do follow what Wynn says about mixing citric acid with silver nitrate just before using them. This avoids the precipitation often seen when these two components are premixed and the solution stored.

I think it's fine. I think ole-squint is mentioning addition of citric acid as an aside, as a separate topic from adding citrates. Citrates have sometimes been added to the salting solution since the earliest days of salt printing. Sometimes even formed in situ by adding sodium carbonate + citric acid. They cause changes the tone and scale ( I'm not a chemist, but suspect it makes silver citrate complexes ). I personally stopped using them early on, preferring the look of plain salt. Some people say that addition of citrates can reduce the need for such long-scale negatives ( I think it's a bit more complicated than that

NedL said:

I think it's fine. I think ole-squint is mentioning addition of citric acid as an aside, as a separate topic from adding citrates. Citrates have sometimes been added to the salting solution since the earliest days of salt printing. Sometimes even formed in situ by adding sodium carbonate + citric acid. They cause changes the tone and scale ( I'm not a chemist, but suspect it makes silver citrate complexes ). I personally stopped using them early on, preferring the look of plain salt. Some people say that addition of citrates can reduce the need for such long-scale negatives ( I think it's a bit more complicated than that

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You are correct, two different topics. Young states that adding sodium citrate results in a warmer color, a lower contrast, and a lower exposure time, hence my original question re potassium vs sodium citrates.

As for the article mentioned by fgorga, Matusz does state that he originally used citric acid on papers unsuitable for salt printing and ended up with his "universal salting recipe": 50 gm citric acid/25 gm salt/water to liter. He goes on to state that he found the treated papers to have a long shelf life before sensitizing, plus "higher shadow density and more pronounced highlights" by double coating with his silver solution (15gm silver/85 ml water).