salt prints - coating fixing & role of citric acid

I've been reading around a bit on salt printing, and like all of these things there are all sorts of recipes with variations both large and small.

I can understand the rationale for quite a few of the variations, but so far I've failed to come up with a satisfactory explanation as to why, in some recipes, Citric acid is added to the Silver nitrate sensitising solution.

In my copy of "Keepers of Light" it is suggested that it can inhibit loss of sensitivity if the paper is sensitised and not used immediately.

I'm also wondering about the inclusion of Sodium citrate in some of the recipes for the salting solution

(When I can track down a properly inexpensive copy of James or Kendall, I will )

any illumination gratefully received ....

If you can find the the book by Eleanor D. Young MECHANISMS OF CONTROLLING
COLOUR AND AESTHETIC APPEARANCE OF THE PHOTOGRAPHIC SALT PRINT you will find her answers there. she does discuss in length about your topic. I think for a while it ( master thesis- which turned into the book) was on the internet as a free download, part of RMIT, grad paper dissertation. I found that link here on APUG. If you do a search on APUG you still might find it. cheers

gzinsel, BrianShaw thank you very much indeed

Christopher James has a very helpful article online, which is actually a chapter from the The Book of Alternative Photographic Processes:

Standard 10% Silver Nitrate & Citric Acid Sensitizer Formula: I prefer this solution formula to the standard mix above, especially if I am
experiencing highlight problems or do not intend to print immediately… the citric acid
makes the solution more acidic, lowers the pH of the sensitizer, and acts as a
preservative.

I've read about a third of young's thesis and she rather demolishes what James has to say

Well on one thing, E. Young says in her thesis that acid additives have no significant effect but they do. James also point out that acid additives stop premature darkening in humid environment. It is very likely Young might have changed it in her book but the point is both have relevant information. I use both sources for salt printing.

I will recommend another source that explains the working mechanisms of citric acid and sodium citrate in salt print. http://unblinkingeye.com/Articles/POP/pop.html

Briefly, adding acid stops the premature darkening of silver nitrate, not completely but enough to prevent problems. Citric acid works well but I have used acetic acid as well. And if I recall correctly it was mentiioned that Mark Ostermann uses nitric acid. All these acids have subtle differences in the print as well, may be you should contact him. You can read more in the article. IMO acid additive is a must, but I add acid before coating not directly mix it in the SN bottle. E.g. I add one drop of %50 citric acid per 2ml of %12 SN before coating.

Sodium citrate increases the reduction of silver, regardless of the process. You can use it with other silver processes too. So more sodium citrate in the gelatin you get faster exposure times, higher contrast, lesser dynamic range. It also effects the color as you read in Young's thesis. I prefer the color of the prints with sodium citrate rather than the ones without it. Depending on the tonal range you require you can adjust sodium citrate content. In the article you will find more about it. I prefer to work with the formula in James's book, but it demands very dense negatives aroung logD3.0

Regards
Serdar

Well Fox Talbot didn't use citric acid in his photogenic drawings and he discovered it.

I'll leave the technical and historical debate to those who have actually made salt prints (I haven't even uncapped my Silver nitrate yet), but I'll follow this thread with interest if it continues.

Citric acid serves as a preservative (silver solution) and results in change of colour the latter is my personal observation. Have both the James book and Youngs thesis. Young has a more scientific approach and James often uses second hand information both are great sources though. If you gold tone the print the color shift caused by using citric acid is irrelevant. The choice of paper or wether one uses arrowroot or gelatine sizing is much more important than the choice between citric acid or non citric acid silver solution.

It is important to get the work of others into perspective. The James book is a useful source of reference, but only as a starting point, because as already said it often uses second hand information. If you write a book about alternative processes, it doesn’t mean you are an expert on these processes, but just good at compiling information sourced from others. With regard to Young, this like many other university thesis, is a regurgitation from many other sources and often lacks practical experimentation with what is stated. Never believe what you read, including what I write here. If you want to have a better understanding about the colour of salt prints, experiment for yourself, again and again and again.

cliveh said:

Never believe what you read, including what I write here. .

Click to expand...

I am the least credulous person of my acquaintance, Clive ... But are you a Cretan by any chance ?

pdeeh said:

I am the least credulous person of my acquaintance, Clive ... But are you a Cretan by any chance ?

Click to expand...

I was born in England, but have visited Crete.

Helau hello... I am glad I found that information. Ok after reading a lot about salt printing and spending a lot of money on silver nitrate and trying out different formulas... I have now a few questions regarding citric acid using with silver nitrate. Yes I need the citric acid and I use a 10% solution in a combination with the 12% Silver Nitrate solution. I mix them 1:1 and contrasting color are amazing. The only problem is the coating. I sometimes end up with kind of strange coating marks (see picture)... I don't have that when I don't use the citric acid at all. For salting solution I use 20g Ammonium Chloride with 20g sodium citrate and 7g gelatine and 1 Later of water. Any suggestion? Thank you, Jan

Hello Jan,
Welcome to APUG!

I've seen this problem many times when working with arrowroot sizing, but not as often when working with gelatin.
It is caused by too little silver nitrate in relation to the amount of salt in the paper. The light areas ( nearly white ) are areas where all the silver nitrate reacted with the salt, leaving no excess. There must be excess silver nitrate for the process to work.

Note that when you mix 12% silver nitrate with 10% citric acid, you end with 6% silver nitrate and 5% citric. 6% silver nitrate is pretty weak for a salt print sensitizer.

Here are some possible solutions:

1) start with 24% silver nitrate and mix it 1:1 with your 10% citric acid. ( I recommend this, it is what I usually do )
This will be 12% AgNO3 and 5% citric acid coated on the paper.

If you do not want to mix stronger AgNO3 ( maybe you used all your AgNO3 to make your 12% solution, or maybe you purchased 12% solution, ), here are some options:

1b) use stronger citric acid solution and add less of it. if you make 40% citric acid, then you can mix 7 parts 12% AgNO3 with 1 part 40% citric. This will dilute the AgNO3 less and still have 5% citric in the result.

2) after coating your 6% silver nitrate, let the paper dry in the dark for about 20-30 minutes, then apply a 2nd coat ( or increase to 3 coats if this is not enough ).

3) after coating your 6% silver nitrate, let the paper sit in dark for 20 minutes, and then WASH it in several changes of water. This will remove any excess salt. Then let the paper dry completely ( I usually wait at least 6 hours, and have never tried to hurry it with a hair drier ), then coat again with a 1% solution of silver nitrate, let dry again, and print.

The 3rd option takes longer because you have to dry the paper twice. The second coat of silver nitrate assures there will be excess. It often works in situations where everything else fails, but I've found it can also be difficult to get the strongest possible darks with this method.

Good luck and have fun!

Ned

Dear Ned,

thank you for your long answer! I mixed new silver nitrate as 24% solution and my problem is gone!! Thank you so much for your help on that. Another APUG user had a similar idea about my coating problem.
I have one more question and that is about fixing the print. I make pretty big salt prints about 22 x28 inches in size. I use Sodium Thiosulfat to gather with Sodium Carbonate for fixing (about 1 gallon). I use two fixing baths each 5 minutes. How meany pictures do you think I can fix in that solution? Would Ammonium Thiosulfat together with a few ml Ammonia better? Is there any way to see when a picture is completely fixed?
Thank you for your help.
Jan

Ok my salt prints have improved big way. I have one more question. It seems like my pictures are yellowing in the washing bath quite a bit... what causes that? How could I prevent it? Any suggestion? Thank you, Jan

Jan Schlegel said:

Dear Ned,

thank you for your long answer! I mixed new silver nitrate as 24% solution and my problem is gone!! Thank you so much for your help on that. Another APUG user had a similar idea about my coating problem.
I have one more question and that is about fixing the print. I make pretty big salt prints about 22 x28 inches in size. I use Sodium Thiosulfat to gather with Sodium Carbonate for fixing (about 1 gallon). I use two fixing baths each 5 minutes. How meany pictures do you think I can fix in that solution? Would Ammonium Thiosulfat together with a few ml Ammonia better? Is there any way to see when a picture is completely fixed?
Thank you for your help.
Jan

Click to expand...

Instead of trying to fix it, which will destroy all colour, why not just stabilise with a super saturated solution of salt.

Jan Schlegel said:

Helau hello... I am glad I found that information. Ok after reading a lot about salt printing and spending a lot of money on silver nitrate and trying out different formulas... I have now a few questions regarding citric acid using with silver nitrate. Yes I need the citric acid and I use a 10% solution in a combination with the 12% Silver Nitrate solution. I mix them 1:1 and contrasting color are amazing. The only problem is the coating. I sometimes end up with kind of strange coating marks (see picture)... I don't have that when I don't use the citric acid at all. For salting solution I use 20g Ammonium Chloride with 20g sodium citrate and 7g gelatine and 1 Later of water. Any suggestion? Thank you, Jan View attachment 178703View attachment 178704 View attachment 178703View attachment 178704

Click to expand...

Wow! I saw you and some of your work when you were in Norway Jan, it was excellent it would be great to see you and your salt prints here soon!

I would love to see some of these 22x28 inch salt prints.... and it would be a lot of fun to see the printing process.

Warning: this long post is not going to answer your question about how many prints a gallon of hypo can fix. I don't know the answer. My guess is that it might fix quite a few prints because there is not much silver left to be fixed on a salt print. But I always use hypo as 1-shot and have never tried to reuse it. And I don't know the answer about yellow stains appearing in the wash, and can only say that stains appearing in the wash is a common problem. When I first started salt printing, I was surprised to see stains appear when I washed with well-water... I thought there would be nothing left to react after fixing. Washing with RO (reverse-osmosis) filtered water made a very big difference in staining during the wash.. so you can try that or try washing in distilled water.

More than a year ago, I sat down and wrote a very long response to this original thread: "role of citric acid". It's much more complicated than just "it keeps the highlights clear" or "it acts as a restrainer" -- there are interesting questions, like whether the citrate ion plays a part in image formation or the effect is mostly hydrophilic. I deleted the post because it got too long and convoluted. Writing about fixing salt prints could end up like that!

If you read all the instructions that have been written about fixing salt prints, the one thing that is clear is that they are all over the map. Some use strong 10 or 15% solutions of hypo, some use 1 tablespoon per liter. Some go for 3 minutes and some for 10 minutes, two baths or one. Some report extreme bleaching so you must heavily overprint, and some report very little bleaching. ( Pdeeh - from the other thread - I'm pretty sure I've read of some people using dilute rapid fix successfully ). And on and on. And Clive will encourage you not to fix them at all, or use potassium bromide or iodide to stabilize the prints ( like Talbot! Even after Hershel told Talbot about sodium thiosulfate, he continued to use KBr and the fact that some of those prints exist today shows that it can work ).

Here are some thoughts:

• There are so many variables that everyone is probably correct for their own version of salt printing, and there is no "one size fits all" answer.
• If the paper is well-sized so that everything stays up on the surface, then 1 Tablespoon hypo / liter, two baths for 3 minutes each, is probably sufficient to remove all the residual silver chloride. ( This from Loris, who has made many successful prints. This is what I do too - but I don't pretend it solves all problems! )
• The importance of good washing at the end is probably underestimated. Many of the historical salt prints that have survived in best condition are from people who used extremely long washes ( sometime days! ).
• Toning the print greatly reduces the amount of fading in the fixing step.
• Amount of fading in the fixer depends on many factors, like sizing and depth of printing. I don't know if a pinch of sodium carbonate in the hypo really decreases fading. I've seen plain salt prints that hardly fade at all and others that fade badly. I'm not convinced that slightly acid or alkali hypo is the most important factor.
• Troubles come when silver nitrate, or silver chloride, or silver sulfamate byproducts of fixing get left in the paper. I think the worst problems happen when sizing is inconsistent, and silver nitrate seeps in underneath or deep inside the sizing and reacts with various things in the paper ( salt in the plain paper, the original paper sizing itself, or other compounds inside the paper ). The fixing step might have difficulty getting underneath the sizing to make these soluble, or it might even cause problems by making light-sensitive byproducts in/under the sizing that can't be washed out; or the damage might already be done prior to fixing, with insoluble silver compounds embedded underneath the sizing that will turn into stains during washing or into stains when exposed to light later.
• Many problems with staining and blotching can't be solved by longer or stronger fixing.
• Lots of problems show up during the washing stage.

Different people use different fixing regimes, and never seem to be shy about saying "what works" on the internet. But I wonder how many people mask the borders ( instead of letting them go black ) or do other testing, so that they'd really notice if there was subtle fogging/staining in the highlights. It's pretty hard to make a salt print without any stain or fog.

All of that and I don't know the answer to Jan's questions. What I know for sure is that there are so many variables that it's hard to generalize. Things that matter to fogging and fixing: type of paper, how much citric acid and/or citrate, type of sizing and how it is applied, how salt is applied ( soaking v floating v brushing on ), whether the paper is acidified, etc. The most important thing seems to be the original paper and the sizing that was applied at the paper mill.

Not sure if any of this is helpful. A long-winded way of saying "it depends"

I think it's such a helpful summary Ned that it deserves a thread of its own.

NedL said:

I would love to see some of these 22x28 inch salt prints.... and it would be a lot of fun to see the printing process.

Different people use different fixing regimes, and never seem to be shy about saying "what works" on the internet. But I wonder how many people mask the borders ( instead of letting them go black ) or do other testing, so that they'd really notice if there was subtle fogging/staining in the highlights. It's pretty hard to make a salt print without any stain or fog.

Click to expand...

Dear Ned,

Excellent point. Not many people mask the borders so they do not see the subtle fog. If you use TF-4 or similar alkali ammonium thiosulfate fixers, I believe there won't be any fog. But I cannot confirm this since I have no access to TF-4. So I had to solve the problem using sodium thiosulfate.

I have changed my workflow since I had problems with fogging even using hahnemühle platinum rag papers. You have done extensive testing on fogging with salted paper in the forums. You might try this too. I am confident this method works. I have also tested this with buffered and unbuffered papers.

• Salting/sizing solution - Choose whatever you like (I have tested 4 different chloride salts. K, Na, NH4, Zn and rock salt)
• For 8x10 print area I use 1,5 to 2ml %12 silver nitrate (depends on the paper) + 2 drops of %50 citric acid per ml + 1 drop of %1 Food coloring (brilliant blue, tartrazine, I even used bromocresol purple indicator) + I also use glycerin but it is not necessary
• Expose for normal duration. No bleach will occur in any steps.
• Wash in few changes of "tap" water, until the excess silver nitrate is turned to different salts and washed away. Preferably wash the print face down, since the silver salts will precipitate.
• Wash in still two changes of 20-25C tap water for 10 minutes face down, wash until the print turns to yellow-brown tones. Warmer the better, not hot enough to dissolve gelatin.
• Fix with salt. Not %1 percent not %3 percent with a pinch of citric acid. Wash the print in %20 Ammonium chloride for 3-5 mins. You will see a color change to lighter yellow-brown. (%20 Ammonium chloride is reusable for more than 10 prints. You can sun it filter the silver precipitate and add more amm. chloride and continue using it.)
• The reason is silver chloride is more soluble in the presence of ammonia ions. Sodium chloride only helps to convert excess silver nitrate. High concentration ammonium chloride converts excess silver nitrate to silver chloride and also dissolves unexposed silver chloride. http://www.saltlakemetals.com/Solubility_Of_Silver_Chloride.htm
• Rinse in water to remove ammonium chloride from the paper. Critical step for fixer longevity.
• Tone with alkali gold toners if you like. (Thiourea toners will stain at this stage)
• Fix in sodium thiosulfate. I am using undiluted TF-2 alkaline fixer. I have fixed for 2,4 and 8 minutes. All work adequately. There will be no bleaching.
• Wash and tone in thiourea-gold toners if you like.
• Since it is an alkaline fixer, hypo clear isn't essential, you can skip it or if you prefer do it.
• Wash 30 mins.

To test if there is visible fog, or some light sensitive silver left in the paper I have left the papers under the UV for 30 mins when they dried.
I am confident this is a fog free method.

Regards
Serdar

Serdar,

I'm happy to see you here, I have learned so much from your posts here and on the Alt.Photo mail list. Some of my normal habits came from your suggestions!

It is very interesting to see your washing sequence prior to fixing. In the past six months I also started using a long plain water wash prior to salted water... and I know that several printers over at the "Calotype Society" also do this. So I'm already convinced that it's best to wash as much AgNO3 out as possible prior to converting what is left to silver chloride. Your point about ammonium ion makes good sense. I will order some ammonium chloride and try your wash/fix instructions. I'm looking forward to trying it.

I've had a particularly difficult time with arrowroot size, because it tends to sink further into the paper and pulls a lot of salt down with it. So it needs more AgNO3 to sensitize (because there is more salt) and it's more prone to fog and staining problems because solutions are absorbed deeper into the paper. But the prints are so beautiful I hate to give up on it. I will try your sequence with that too. So far I have made many dozens of arrowroot-sized prints on many kinds of paper, some look very nice but none have been without problems. It's easier to get a clean print w/ gelatin, or with no added size if the paper is good to start with.

Does your tap water have any chlorine or chloramine in it?
Does the glycerin help with coating smoothly?

Thanks!
Ned

Ned,

I am also doing and testing what many others tell in their books and on the websites. A while back I noticed the fog with hahnemühle papers, then I exposed the paper to UV light. The fog got darker, I have applied farmer's bleach to test if it was silver, and it was silver. Although the prints looked clear, when left under UV for 30 mins the borders were exposed. So it clearly showed there was something wrong or inadequate in common practice. I have tested various washing, salt washing, multiple salt washing steps and the results were the same. Some silver was left behind. Sodium thiosulfate was not removing all the silver chloride even in two step fixing.
In terms of washing, if you put the print in salted water you instantly create silver chloride trapped in fibers. If you wash in tap water which is chlorinated but the concentration quite low, initially the silver nitrate on the surface is converted and precipitated. But still some silver chloride will be created and trapped in the fiber, which is not exposed to light . To remove that I decided to try fixing with salt like early Tablot's works, than fix in hypo and stabilize it. If you look at the amount of silver chloride soluble in various solutions, using sodium chloride for initial washes is not very effective, but higher concentration of ammonium chloride performs better.

I have tested the method with different amount gelatin sizing (%0,2 to %2,5), casein and no sizing. I hope it works with arrowroot too. I believe, it is not a problem of how much salt and sizing sinks in the paper but the method of removing.

Glycerin works as humectant and weak emulsifier. I have good result with high humidity, it also helps printing slightly faster. But in more humid environments it caused problems for some. When I used bromocresol purple to colorize the silver nitrate solution it was mixture of alcohol, silver and citric acid. Glycerin helped with the even coating, I use 1 to 2 drops. I still use it with food coloring.

Regards
Serdar