Salt print fogging tests

I'm back in test mode for a few days instead of printing mode with salt prints.

I'm putting this here in case anyone is interested. If you want to suggest a different combination, or want me to try a different kind of paper, let me know.

Background:

My impression is that not very many people making salt prints these days try to get clean borders. Many people like to print with “dirty” black borders, or have brush strokes show. Other people cut out the finished print and mount it. Since not many prints have perfectly paper-white highlights, this means that if there is subtle fogging in the areas coated with silver nitrate, it could go unnoticed. My guess is that as long as the highlights are bright, most people are happy and would not notice very slight overall fogging... they'd assume the highlights were slightly printed in – which is a common way to know the print is done exposing. Subtle fogging becomes a problem if you want to print clean borders.

Some months ago Pdeeh made a salt print with a nicely masked border, and the white area around the print where the silver had been coated eventually fogged – well after the print was washed and dried. Recently I've been making prints with rubylith masking and paying close attention to the borders, and while they are mostly clean enough to look nice, I have not made any prints where the unexposed border area -- coated with silver nitrate but not exposed to light – is perfectly paper white upon close examination. Fortunately, with my favorite paper and salting it is a very subtle problem, but it would be nice to know more about it.

The other day I made this print which has egregious fogging. The highlights are obviously ruined. I'm sure any salt printer who made this print not be happy with it. It was on a paper and with a salting formula I hadn't tried before. It was on Magnani Mills Revere Platinum, used ½% sodium citrate, and used pigskin gelatin – all things I don't normally use. The stain increased throughout the process, visibly getting worse during washing. You can also see a known problem with this paper: the sizing caused blotches to appear during the wash stage.



With such an extreme example of fogging, I decided to try a series of tests to see what caused it, and maybe to learn more about fog in general.

The tests:

This morning I cut 2x2 inch pieces from each of 3 kinds of paper. I just finished salting each kind of paper 6 ways:

• 2% salt
• 2% salt + ½% sodium citrate
• 2% salt + 1% ossein gelatin
• 2% salt + ½% sodium citrate + 1% ossein gelatin
• 2% salt + 1% pig skin gelatin
• 2% salt + ½% sodium citrate + 1% pig skin gelatin

I'll coat each piece with 12% AgNO3 + 6% citric acid, leaving an uncoated area on each.
I'll expose each for about 5 minutes in the sun, so that there is:

• an uncovered area
• an area coved by red rubylith ( in case sunlight getting through it is a factor )
• an area covered by black plastic

I have a guess about what caused the extreme fogging, but we'll see. Feel free to chime in with your guess! I'll coat the paper with silver and expose sometime in the next few days.

One thing I don't have enough samples to control is temperature. The printing frame can get warm on a sunny day.... but I've made lots of prints with very little fog so at least that's not the cause of this extreme version of fogging. But it wouldn't surprise me if it is a factor in more subtle fogging.

BTW, it did occur to me that I can't dip my brush into silver nitrate between coating these, because some of the salt/gelatin coatings would carry over. So yesterday I bought a dozen inexpensive foam brushes. I'll coat a dozen at a time, without re-dipping into the silver nitrate, and then wash the brushes very carefully before coating more.

There is also a bit of a lesson here about alt processes. I know I've “preached” a little about using enough citric acid in salt prints to avoid fog. I did a series of careful tests with citric acid when I first started, and it made a big difference. But there are so many variables! Everyone who prints has different water, uses different salts and chemicals and papers, different humidity and temperature and source of UV... that's why reading about what others do is sometimes not very helpful; or what works for one person doesn't work for another. The only reliable way to learn is to try things yourself!

good stuff Ned!

important to note that the print of mine referred to had been stored for about 6 months in total darkness when the fogging was noticed.

Right! That's an important point and is what got me worrying about this in the first place. I will save these tests to look at again in 6 months and a year.

I always mask with rubylith and/or goldenrod (and not just for salt printing) precisely because it will immediately show you if your highlights are degraded. I'd have to check my notes, but I recollect that I was not happy with Revere Platinum when I tried it. I had paper from three different iterations of this paper, and the latest may behave completely differently. You might try an acid soak for the paper -- oxalic or sulfamic.
I brush platinum/palladium, but I prefer a glass rod for salt printing -- perfect coating and no chance of contamination.

Thanks Philip, no need to check your notes. I saw some of your old comments on the B&S forums and indeed you noticed blotching and some black spots with this paper. Other people noted that it seemed to get worse near the end and my batch is from some of the last made. If I try it again for salt, I'll try the sulfamic ( although it is supposed to be unbuffered! ) and also pre-size.

The recent reintroduction of Revere Platinum is made by different mill, I'd love to know which one. I haven't ordered any yet.

Um. . . . the paper is where the foggent is. manufactures put in a lot of B>S into their paper. what you want to buy is 100% rag, NOT 100% acid free. there is a difference. acid free paper may or may not be 100% rag, but it will contain buffing agents like calcium carbonate or other fillers that interact with the salt solution, creating fog. I think Mike W. talks about this somewhere, and also on unblinkng eye , I thought i read an article. Also in your tests, you need to test whats in your paper. THE PAPER IS THE KEY!!!!!!!I have always had good success with Twin Rocker hand made paper out of indiana. they are expensive

greg zinselmeier said:

Um. . . . the paper is where the foggent is. manufactures put in a lot of B>S into their paper. what you want to buy is 100% rag, NOT 100% acid free. there is a difference. acid free paper may or may not be 100% rag, but it will contain buffing agents like calcium carbonate or other fillers that interact with the salt solution, creating fog. I think Mike W. talks about this somewhere, and also on unblinkng eye , I thought i read an article. Also in your tests, you need to test whats in your paper. THE PAPER IS THE KEY!!!!!!!I have always had good success with Twin Rocker hand made paper out of indiana. they are expensive

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Revere Platinum was designed for platinum printing -- unbuffered 100% cotton. Even this does not guarantee success. Ned is right -- there are a huge number of variables, including environment, materials, and workflow.

Oh I wish I wish I wish there was only a single variable affecting salt prints

Hi Ned,
Have you ever tried Fabriano Artistico aquarel paper (cold pressed, fine grain)? I had good results with this paper. There are two versions:
- white (a bit off-white/yellow, like slightly toned paper, not suitable for all kinds of images)
- extra white (= really white, I like this one best).
Bert from Holland

I think my fogged print was made on natural white Artistico,

that is true, there are other variables besides paper that cause fogging, IMO, paper is usually the first culprit, second is contamination. I use a push rod, not a brush. yes you are correct, your work flow needs to be sterile like, and efficient. If you have correct paper and a clinical work flow, starting out with non contaminated materials and space, then with proper execution, you should ( in theory)be able to make a non fogged print, with clean highlights. now, that always doesn't happen for me either, but I do have some prints that are perfect ( look as I printed them 15 years ago) no degrading! although others/some haven't been so kind

In your new experiment, I would expect fogging under the black plastic. Most of this material is not truly impervious to the UV spectrum.

I agree that paper is one of the most important factors in salt printing. Not only for clear highlights, but for everything about how the print will look including color and how the print will respond to different toners. I suspect this test might show that the kind of gelatin matters, but we'll see!

Meaning to try the Fabriano Artistico papers for a long time.

Jim Noel said:

In your new experiment, I would expect fogging under the black plastic. Most of this material is not truly impervious to the UV spectrum.

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Thanks Jim... I haven't exposed yet. I'll think of something better to completely block light on a portion of the paper.

aluminium foil would do the trick I think

NedL said:

I agree that paper is one of the most important factors in salt printing. Not only for clear highlights, but for everything about how the print will look including color and how the print will respond to different toners. I suspect this test might show that the kind of gelatin matters, but we'll see!

Meaning to try the Fabriano Artistico papers for a long time.



Thanks Jim... I haven't exposed yet. I'll think of something better to completely block light on a portion of the paper.

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Artistico is buffered, so best to give this paper an acid soak.

Update

I exposed the first 9 tests today. Here they are being exposed:



Processed as per normal, but without any toning:

• 3 minutes wash in water w/ a pinch of salt
• 2 x 5 minutes wash in distilled water
• 2 x 3 minutes fix in hypo
• brief rinse
• 3 minutes in 1% sodium sulfite
• wash for 1 hour in many changes of RO water

Right now they are drying.

I'm already glad I did this because there is already a result I didn't expect.

1st result:
Rubylith works great, as expected. But nice to be reassured it is not a factor.

2nd result:
2% salt with 1/2% sodium citrate and 1% pigskin gelatin on Magnani Revere Platinum fogs badly and it gets even worse during the wash. This is the same combination that prompted me to do these tests and it was expected to fog horribly.

Results that surprised me:
2% salt with 1% ossein gelatin on Magnani Revere Platinum also fogged horribly, getting worse during wash.
but
2% salt with 1% pigskin gelatin and no sodium cittrate on Magnani Revere Platinum does not appear to have any fog at all!

Here they are washing:



Numbered samples are Magnani Mill Revere Platinum. You can see the awful fog on numbers 1 and 2.
1= salt with pigskin gelatin and sodium citrate
2= salt with ossein gelatin
3 = salt with pigskin gelatin

There are going to be some interesting results with the more subtle fog, but I'll wait until they dry to evaluate.
There are also 9 more samples to expose with other combinations... hopefully tomorrow.

So... already interesting!

When they are all done, I'll summarize results here. Maybe I'll try to scan them, but I'm not very good at that... we'll see.

P.S. If you want a mystery to ponder, I just checked and that stain/fog on #1 is what it looks like in the photo...it does not have a straight edge and it does not reach the edge of the brushed on silver ( like #2 does ). When I brushed on the AgNO3, the left side of each sample was masked with tape. So the area covered with silver nitrate has more or less a straight edge on each sample. The dark areas on sample number 1 clearly show that the brushed on silver nitrate extended beyond the area that fogged. Something to do with the paper sizing perhaps?...

thanks for sharing all your hard work. I will be following your results!! thanks again for taking the time to share. your examples are great.

Thanks! I did finish the exposure and processing on Wednesday... need to find time to write or display the results. The really awful fog only appeared with some combinations on the old Revere Platinum ( which is no longer made ), but more subtle fog appeared on most of the samples.

Here are the results. All in all pretty disappointing I think. Greg was right that the main factor in the really awful fogging was the paper, but there is a lot of variation in the more subtle fogging.

I made up a subjective scale to grade them:

0 = no visible difference from paper white, regardless of light and angle, no matter how hard you look.
1 = very slight, need to look carefully in good light to notice
2 = mild, but noticeable if you look for it
---
3 = noticeable fog, not hard to see
4 = bad fog
5 = awful fog/stain.

0 and 1 are probably okay for printing, 2 is marginal, and 3 or higher would certainly damage highlights and prevent clean white borders.

All have 2% salt and were sensitized with 12% AgNO3 and 6% citric acid. When sodium citrate was added to the salting solution it was 0.5%. When gelatin was added it was 1%. Each sample was floated on salting solution for 3 minutes. The left side of each sample was not sensitized with silver nitrate.



First set on Magnani Mills Revere Platinum ( this paper mill closed. The new Revere Platinum is a different paper, not the one tested here. )

1. Salt only. Fog: 5
2. With sodium citrate Fog: 5 ( ran out of AgNO3 when coated )
3. With ossein gelatine Fog: 5
4. With sodium citrate and ossein Fog: 5
5. With pigskin gelatin Fog: 3 (see note 1 )
6. With sodium citrate and pigskin gelatin Fog: 5

Next set on Lana Aquarelle hot press 300gsm

7. Salt only. Fog: 4
8. With sodium citrate Fog: 1
9. With ossein Fog: 3 (see note 2 )
10. With sodium citrate and ossein Fog: 4
11. With pigskin gelatin Fog: 0
12. With sodium citrate and pigskin gelatin Fog: 1

Next set on Canson Universal Sketch ( see note 3 )

13. Salt only. Fog: 2 ( but paper has internal fog not visible on surface )
14. With sodium citrate Fog: 1
15. With ossein Fog: 2
16. With sodium citrate and ossein Fog: 1
17. With pigskin gelatin Fog: 2
18. With sodium citrate and pigskin gelatin Fog: 1

Some notes:

1The stain/fog on the Revere Platinum “blooms” from blotches...you can even see the stain spread as the print is washing. Even though #5 looks relatively clean, there are clean areas on other samples as well, and there is a hint of a blotch starting to form. I don't trust that this combination would be trouble-free. Some of these were not visible at all until the wash, and all of them got worse during the wash.

2My normal "recipe" for this paper is 2% salt, 0.5% citric acid and 0.6% ossein gelatin. It's probably a 1 or 2.

3I know from earlier tests that the canson universal sketch will fog without citric acid in the sensitizer.

The addition of sodium citrate does matter. pH buffer solutions are made by mixing citric acid with sodium citrate. These tests used 0.5% sodium citrate and it is likely that the results would vary if we changed the ratio of sodium citrate to citric acid in various ways. It might be a good way to home in on a fog-free print for a particular combination of paper and gelatin.

These tests could be done again after acidifying or pre-sizing the papers or both.

I'll put these away and see what they look like in 6 months and a year.

What I learned from all this is that subtle fog is more of a problem than I realized.

Thanks for doing this. When you say pigskin gelatin are your referring to simple Knox gelatin from the super market or a more refined form like that available from Dass? What is your source for this?

GregW said:

Thanks for doing this. When you say pigskin gelatin are your referring to simple Knox gelatin from the super market or a more refined form like that available from Dass? What is your source for this?

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Hi Greg,

I used "Superclear" gelatin from Custom Collagen. It dries perfectly water clear. However, if you use a brush to sensitize the paper after it has been coated with this gelatin and dried, there is a tendency for it to foam a little. I haven't decided yet if this is a problem. The ossein gelatin was photo grade from B&S.

Thanks Ned, Going to give #11 a try. My last attempt at SP ended with badly fogged images. PS I coat with a glass rod.
greg

Some additional information that might or might not be of use to future readers of this thread.

I have continued some tests:

On a sheet of Lana Aquarelle from the original batch of salting that led to this thread ( 2% salt, 0.5% citric acid, 0.5% sodium citrate and 1% pigskin gelatin ), I managed to make a print with zero fog by increasing the citric acid to 10% in the sensitizing solution. The speed of printing was noticeably slower, and toning was a little difficult because there was not quite the depth of printing that would be best. Still, it made a good print.

On the very next day, I repeated this exactly with another piece of Lana Aquarelle and got some awful blotches ( some extending beyond the area that was sensitized! The blotches are largely internal rather than on the surface ) and there was fogging along one edge only ( the edge that was outermost on the original sheet ).

The weather was hot both days, although it was a little hotter and I started the print a little nearer noon on the second day.

So that's pretty frustrating, because this kind of inconsistency can't be solved by careful testing. There are rumors that another company has purchased the mill that makes Lana Aquarelle, and that production of the paper has stopped due to complaints about quality. I did not see any blotches on a batch purchased in 2013, and really liked the paper, so I bought this larger batch last year, and am having problems with it.

Yesterday I cut up some 5x7 pieces to see if arrowroot sizing might keep the sensitizer far enough off the paper to avoid some of these problems. Two of these were acidifed in 10% sulfamic acid and the produced quite a few bubbles for the first minute or two, so even if there is not a heavy carbonate buffer, there appears to be some alkaline component. I think what's happening is that the sizing is inconsistent and sometimes the sensitizer is getting wicked down into areas that are alkaline. The strong 10% sulfamic acid really changed the surface characteristics of the paper, making it more absorbent and making the paper fragile and prone to damage. I'll update more later about the arrowroot after I've made some more prints. I kept the arrowroot salting/sizing solution on the acid side ( some old recipes have an excess of sodium carbonate, put in to form citrate from citric acid.... I didn't do that ).