Salt Printing: Dark Stain

[nmp]

I was doing some initial tests for salt printing process I am trying to learn/develop and came across staining in the highlight areas, as I guess anyone new to this does. What I noticed was my test prints were slightly off-color already as they came out of drying post-AgNo3 application. That got me doing an experiment to see what the source of this is. I also noticed that in some areas on the edge where there had been no salt had also browned. Clearly it seemed that AgNo3 is interacting with the bare paper. Does this depend on the type of paper?

So I rounded up some of the various papers I had, cut them in to strips and dipped the ends in AgNo3 (10% solution with 2% citric acid) and dried them in dark. The results are showed in the attachment. As you can see a couple of them are like a mid-tone of fully exposed print. Only Bergger Cot 320 did not show any of this “dark stain.” Luckily that is paper I envisioned ultimately to develop my process on.

Just thought I will share this. Not sure if this is reinventing the wheel or not. But I was surprised.

:Niranjan.

 

[NedL]

Finally a salt print question that probably has a straightforward answer!

Yes, if the tone changes on the paper after the AgNO3 dries, it is the 1st sign of a possible problem. Definitely different papers are different ( as you yourself have proved nicely! ). That COT 320 looks nice. I have some here and still have not tried it.

It's possible that your test could have come out a little differently on some of the lighter stained ones if you'd painted on the AgNO3 on the front side of the paper instead of dipping. Also, adding a little citric acid ( up to about 6% ) to the AgNO3 might make some of them very acceptable. Also, acidifying the paper ahead of time in a weak 2% solution of sulfamic, acetic or citric acid might make some of them work. Also adding a little citric acid ( 0.5 % ) to the salting solution might help a lot. Some people say adding sodium or ammonium citrate to the salting solution can help, and I believe that it worked for them, but I have not seen that myself. If none of those things work, and you can still see a tone change after the AgNO3 dries, it's probably not going to work on that paper.

The paper I'm working with right now (strathmore 500 single ply drawing paper ) does have a visible area where the AgNO3 was coated... almost like it is slightly wet, but it is very subtle and it DOES go away during processing. So a very tiny amount of difference can be okay, but nothing like what is in your test photo.

Have fun ( I've got one washing right now and am about to go tone it )

Cheers!
Ned

 

[Herzeleid]

As far as I know, the only paper without alkaline buffering among the papers you have tested is bergger cot 320. So Ph is the culprit.

As Ned mentioned neutralizing the alkaline buffer with an acid prior to coating, and adding small amount of acid to salting/sizing helps with buffered papers.
I would suggest to use silver nitrate and citric acid separately and mixing them before coating.
Increasing the amount of acid for specific papers stops the the darkening of silver nitrate before exposure.

Regards
Serdar

 

[pschwart]

Silver nitrate on the back of the paper will result in stains, so the first order of business is to retest coating only the front. You will also want to use only unbuffered papers, or use an acid presoak to neutralize buffered papers. Sulfamic or oxalic acid work well.

I was doing some initial tests for salt printing process I am trying to learn/develop and came across staining in the highlight areas, as I guess anyone new to this does. What I noticed was my test prints were slightly off-color already as they came out of drying post-AgNo3 application. That got me doing an experiment to see what the source of this is. I also noticed that in some areas on the edge where there had been no salt had also browned. Clearly it seemed that AgNo3 is interacting with the bare paper. Does this depend on the type of paper?

So I rounded up some of the various papers I had, cut them in to strips and dipped the ends in AgNo3 (10% solution with 2% citric acid) and dried them in dark. The results are showed in the attachment. As you can see a couple of them are like a mid-tone of fully exposed print. Only Bergger Cot 320 did not show any of this “dark stain.” Luckily that is paper I envisioned ultimately to develop my process on.

Just thought I will share this. Not sure if this is reinventing the wheel or not. But I was surprised.

:Niranjan.

 

[nmp]

Thanks to all for the responses.

To summarize:

1. Not all papers are created equal. Alkali buffers used for archival purposes can make the papers react with the AgNo3 in dark even in absence of external salt, causing them to stain. From that perspective, Cot 320 is virtually non-active – as might be expected for being un-buffered.

2. Which side is coated matters. Is this because there may be different amounts of the buffering compound on one side vs other, the result of the manufacturing process (felt vs wire side.)

3. Each paper might have its own optimum citric acid level in the sensitizer and/or salt. One formulation won't work for every paper. Also better to add acid just prior to coating.

4. Pre-acidify the paper. Preferably with sulfamic acid (came across Serder's extensive work on its efficacy and advantages.)

New Experiments:

A: Brush-coated on one side based on the suggestions. The results were fairly close to those dip-coated. Unfortunately I did not scan them in time so no images to show (see B.)

B: The above test-strips were left out in the daylight for some time and I noticed every one of them had turned significantly darker, including COT 320. So I let them sit the Sun for some more time which darkened them even more. Some of them looked like having achieved a fully exposed Dmax - particularly the Arches Aquarelle (which had second least “dark stain” after Cot 320) turned darkest of them all to a deep red. Sure looks like a candidate for salt-free (diet) printing.

(See image -0001)

I am taking these thru fixing and selenium toning and see how they hold up.

C: Finally for acidification, I took strips of 3 papers (x2 for top and bottom sides) :

-Cot 320, for reference
-Strathmore CP which had the most egregious dark stain, and
-Arches Aquarelle which was on the borderline. I like that paper so I want to try and make it work.

Treated them with 3% citric acid (unfortunately I do not have the others mentioned at hand) for about an hour and then washed in tap water, dried. Repeated #1 and #2 on them gave the following results:

Dark Stain: None. All unchanged after AgNo3 coating and drying in dark.
UV Exposure: 20 mins, All POP'ed nicely. There is a slight difference between the two sides of the same paper, although that could be because of the texture.

(See image -0002)


:Niranjan.

 

[Gerald C Koch]

I would suggest using a pH neutral 100% rag bond paper. Papers made from wood pulp can cause problems as they often contain compounds that act as reducing agents which will cause staining. In Fox-Talbot's day paper were made from rags not wood pulp which is a more modern innovation. Such wood pulp papers are the bane of museum conservators like the Library of Congress. They require special treatment in order to make them archival.

 

[nmp]

I would suggest using a pH neutral 100% rag bond paper. Papers made from wood pulp can cause problems as they often contain compounds that act as reducing agents which will cause staining. In Fox-Talbot's day writing papers were made from rags not wood pulp which is a more modern innovation. Such wood pulp papers are the bane of museum conservators like the Library of Congress. They require special treatment in order to make them archival.

I am pretty sure most of the papers I am using are made from 100% cotton and are acid-free etc. The Strathmores I am not sure as I can't find the specs for them, but Arches, Fabraino and Bergger are all made of 100% cotton.

 

[pschwart]

To summarize:

1. Not all papers are created equal. Alkali buffers used for archival purposes can make the papers react with the AgNo3 in dark even in absence of external salt, causing them to stain. From that perspective, Cot 320 is virtually non-active – as might be expected for being un-buffered.

>> The most obvious result of using buffered papers is a weak image

2. Which side is coated matters. Is this because there may be different amounts of the buffering compound on one side vs other, the result of the manufacturing process (felt vs wire side.)

>> If you are seeing a difference it is most likely caused by one side exhibiting more texture which can be more troublesome to sensitize, especially
>> when using a puddle pusher (which work great on a smooth paper like COT320).

3. Each paper might have its own optimum citric acid level in the sensitizer and/or salt. One formulation won't work for every paper. Also better to add acid just prior to coating.

4. Pre-acidify the paper. Preferably with sulfamic acid (came across Serder's extensive work on its efficacy and advantages.)

>> Oxalic acid also work very well (try 1.5% for 3 minutes). I never got good results using acetic or citric, but I didn't do much testing. Sulfamic is
>> a good choice because it's effective, and cheaply available as a tile/grout cleaner.

New Experiments:

A: Brush-coated on one side based on the suggestions. The results were fairly close to those dip-coated. Unfortunately I did not scan them in time so no images to show (see B.)

B: The above test-strips were left out in the daylight for some time and I noticed every one of them had turned significantly darker, including COT 320. So I let them sit the Sun for some more time which darkened them even more. Some of them looked like having achieved a fully exposed Dmax - particularly the Arches Aquarelle (which had second least “dark stain” after Cot 320) turned darkest of them all to a deep red. Sure looks like a candidate for salt-free (diet) printing.

(See image -0001)

I am taking these thru fixing and selenium toning and see how they hold up.

C: Finally for acidification, I took strips of 3 papers (x2 for top and bottom sides) :

-Cot 320, for reference
-Strathmore CP which had the most egregious dark stain, and
-Arches Aquarelle which was on the borderline. I like that paper so I want to try and make it work.

Treated them with 3% citric acid (unfortunately I do not have the others mentioned at hand) for about an hour and then washed in tap water, dried. Repeated #1 and #2 on them gave the following results:

Dark Stain: None. All unchanged after AgNo3 coating and drying in dark.
UV Exposure: 20 mins, All POP'ed nicely. There is a slight difference between the two sides of the same paper, although that could be because of the texture.

(See image -0002)


:Niranjan.[/QUOTE]

 

[Gerald C Koch]

Another possibility would be if the paper contains sizing chemicals. For example watercolor paper uses gelatin as a sizing material. Kodak found that whether a batch of gelatin was suitable depended on what time of the year the cow was slaughtered. Gelatin from cows that eaten wild onions in the Spring could not be used for emulsion making as the gelatin contained too many sulfur compounds which caused fog.

 

[NedL]

That's pretty wild! Maybe if the cows ate shallots we'd get reversal paper

The last two papers that worked when acidified might also work if you just add some citric acid to the AgNO3 prior to sensitizing.

It's interesting how different papers produce different colors. They do that when salted too.

 

[Peter Schrager]

thanks for a great thread. I appreciate your research as good salt prints are hardest to make

 

[nmp]

Another possibility would be if the paper contains sizing chemicals. For example watercolor paper uses gelatin as a sizing material. Kodak found that whether a batch of gelatin was suitable depended on what time of the year the cow was slaughtered. Gelatin from cows that eaten wild onions in the Spring could not be used for emulsion making as the gelatin contained too many sulfur compounds which caused fog.

Yep...my money will be on the sizing. Sulfur compounds will make sense for the dark stain - that would be akin to toning where you get silver sulfide (or some other variations) as a result. Most paper makers have their own proprietary brew for sizing so the paper dependence is not a surprise. Additionally this reaction of silver nitrate with sizing compounds must like alkaline environment. Hence acidifying the sensitizer and/or pre-acidifying the paper seem to eliminate or reduce it.

As far as I know Cot 320 is gelatin sized, but designed for alt processes as it is, they must use a good quality low-sulfur gelatin.

Edit: No I was wrong about Cot 320. It is not sized with gelatin, but gum arabic - per Christopher James' book. Perhaps that makes the difference.

 

[Jim Noel]

I use only 100% linen paper for salt printing and do not have this staining problem.

 

[nmp]

I use only 100% linen paper for salt printing and do not have this staining problem.

Hi, Jim:

I am not familiar with linen paper. Can you please point to a particular brand or type that you are using?

Thanks.

:Niranjan.

 

[nmp]

B: The above test-strips were left out in the daylight for some time and I noticed every one of them had turned significantly darker, including COT 320. So I let them sit the Sun for some more time which darkened them even more. Some of them looked like having achieved a fully exposed Dmax - particularly the Arches Aquarelle (which had second least “dark stain” after Cot 320) turned darkest of them all to a deep red. Sure looks like a candidate for salt-free (diet) printing.

(See image -0001)

I am taking these thru fixing and selenium toning and see how they hold up.

After fixing, the there was the obligatory color change and some bleaching or fading of the intensity of the color. Here is the comparison of before and after fixing. In particular the Arches paper looks like held up pretty good. I guess I will let the pictures speak for themselves.

Next stop - selenium toning.


:Niranjan.

 

[Herzeleid]

Niranjan,

I am using alkaline sodium thiosulfate fixer. Specifically I switched to TF-2 formula. I have tested 2-4-8 and 10 mins of fixing, no bleaching occurs even with extended fixing times.

But if I may add to that, I feel like the dmax is problematic in these samples. Especially fixed Cot 320 sample after fixing, the dmax does not look acceptable for printing, or may be the strip lacks silver.
Since you cannot control the amount of silver nitrate on each strip, I am not sure how this test will give you definitive results. Usually with salt prints I get much deeper blacks.

Regards
Serdar

 

[nmp]

Niranjan,

I am using alkaline sodium thiosulfate fixer. Specifically I switched to TF-2 formula. I have tested 2-4-8 and 10 mins of fixing, no bleaching occurs even with extended fixing times.

But if I may add to that, I feel like the dmax is problematic in these samples. Especially fixed Cot 320 sample after fixing, the dmax does not look acceptable for printing, or may be the strip lacks silver.
Since you cannot control the amount of silver nitrate on each strip, I am not sure how this test will give you definitive results. Usually with salt prints I get much deeper blacks.

Regards
Serdar

Serder,

Mine is 15% sodium thio with 2% sodium carbonate, your basic alkaline fixer from Reilley's book.. TF-2 sounds interesting. I will acquire it or make it (looks like sodium metaborate is the only additional chemical I will need) and be sure to try it. Thanks for the suggestion.

With regards to the Dmax, I agree that these are weak for actual salt printing. However, I want to point out that these tests are based on fairly uncontrolled conditions where none of the variables are optimized. They do not even have external salt applied. Toning will hopefully add some density as well. Looks like I have stumbled upon the so-called "non-salt salt print" as coined by Liam Lawless (Post-Factory Issue 8.) I intend to take a couple of these, most likely the Arches and the COT 320, and optimize them without (first) or with salt (later) and see where they go. Along the way, if I develop a better understanding of the various aspects of the process, that would be icing on the cake.

:Niranjan.

 

[NedL]

Right... it's important to realize that Niranjan's tests were done without salting! Which I think is really pretty neat, and I didn't know that Liam Lawless had coined that term. I need to find a copy of P-F issue 8! Coincidentally, Pdeeh and I have just been discussing 'salt-less" prints with a different sensitizer.

 

[Herzeleid]

Niranjan,

I didn't realize there was no salt, well that explains a lot. Since the topic was salt printing I assumed that there was salt in them. So this is just silver and cellulose, quite interesting.

For TF-2 fixer, 10 gr of sodium metaborate can be substituted with 5,9 gr of sodium carbonate. Making sodium metaborate posts can be found on the forum.

Regards
Serdar

 

[nmp]

Niranjan,

I didn't realize there was no salt, well that explains a lot. Since the topic was salt printing I assumed that there was salt in them. So this is just silver and cellulose, quite interesting.

For TF-2 fixer, 10 gr of sodium metaborate can be substituted with 5,9 gr of sodium carbonate. Making sodium metaborate posts can be found on the forum.

Regards
Serdar

No problems. I did bait and switch. Wonder how one can modify the thread title. It won't let me edit the post anymore.

By the way, if you replace the metaborate with sod carbonate, this becomes similar to what I am using except the sulfite which is same as the hypo clear. Does it help in clearing out the thiosulfate post-fixing better thereby allowing one to skip the hypo clear step, I wonder.

 

[nmp]

Yep...my money will be on the sizing. Sulfur compounds will make sense for the dark stain - that would be akin to toning where you get silver sulfide (or some other variations) as a result. Most paper makers have their own proprietary brew for sizing so the paper dependence is not a surprise. Additionally this reaction of silver nitrate with sizing compounds must like alkaline environment. Hence acidifying the sensitizer and/or pre-acidifying the paper seem to eliminate or reduce it.

As far as I know Cot 320 is gelatin sized, but designed for alt processes as it is, they must use a good quality low-sulfur gelatin.

Edit: No I was wrong about Cot 320. It is not sized with gelatin, but gum arabic - per Christopher James' book. Perhaps that makes the difference.

Someone could have made some money off my bet.

After thinking that perhaps there was some sulfurous toning-like reaction going on between silver nitrate and components of the paper, I wondered if it can be tested if the stains were indeed some silver based compound or metallic silver. To do this I used 1% potassium ferricyanide solution to treat the paper (previously coated with AgNO3 and dried in dark.) If the stains were made of silver metal they should be bleached out by the typical reaction (a la Farmer's reducer):

Ag + K Ferricyanide = Ag Ferrocyanide (white solid)+ K Ferrocyanide (soluble)

But before that I had to remove the excess AgNo3 as it will also react with K ferricyanide to form orange-brown Ag ferricyanide, messing up the experiment. For that a couple of distilled water rinses followed by a 1% NaCl soak made sure that all of the AgNo3 was either removed or converted to silver chloride.


The results are shown on the attached jpeg for two papers, #5 = Arches Aquarelle and #6 = Strathmore Watercolor CP, the former showing faint dark staining and the latter very strong.

A's are control - untreated stains

C's are A's + (pre-rinses + bleach + hypo fix to remove Ag ferrocyanide + final wash) sequence

B's are A's + wash only


Observations:

1. C's are completely clear indicating that the stains are indeed metallic silver and not some AgSx like compounds, as they would be non-reactive towards potassium ferricyanide, as I had conjectured.

2. B's got a little darker for #5, but lighter for #6. Don't know what to conclude except just plain water treatment does something to the image.


Now the question is what is going on when silver nitrate meets the paper.

If there is indeed metallic silver in the paper without any UV exposure, it must be a result of spontaneous reduction of silver nitrate - leading to the possibility that the paper is acting like a reducing agent in the manner of a developer.

After some digging, I learned that cellulose can act as a reducing agent, particularly if it has been oxidized to form aldehydes, acids etc. - not an unlikely outcome of the paper making process. Incidentally, glucose, which is the repeating unit of cellulose, was used as a developer at some point in the early history. Furthermore, the reducing action is catalyzed or helped in alkaline conditions. This explains the greater propensity of the buffered papers for stains and elimination of the same by pre-acification.

The other reducing source could be the sizing agent. AgNo3 is a very prominently used as a "stain" for protein molecules as a way to boost the electron density of specimens for electron microscopy. There are plenty of proteins in the gelatin and other sizing agents.


Comments/observations/caveats welcome. Feel free to poke holes....there are bound to be some!

:Niranjan.

 

[NedL]

That's very interesting, thanks for posting these results.

I was recently thinking about ferricyanide reducer and if it could be useful for the margins of some prints. I have some prints where the border has slight fog because rubylith is not perfect at blocking UV ( i.e. the fog was actually caused by light! ) Maybe I can clean up the margins with a reducer.

Definitely it is the case that just plain water can go both ways. It can wash out soluble compounds ( E.g. AgNO3 ) that could later cause staining.... or it can make the paper environment ready for stain-producing reactions to happen. (there was a url link here which no longer exists) thread was like that... it was just on the verge of having horrible brown stains all over.... and all it took was putting it in some water for that to start happening. My first two tries turned dark brown all over immediately. Adding CA to the salt solution held that off while the paper was dry but as soon as it got wet the stains started to form. That was on plain paper w/o sizing or acidification.

It's pretty common with problematic papers for stains to start showing during the wash after processing. I think it's more than just that the wash is happening in light but also that the water finally gets down deep under the paper sizing and allows stain-forming reactions to take place there. ( I can't prove that is true, but I've seen those stains get worse while the print is drying, and I dry them in my closet to prevent dust... where it also happens to be dark. )

 

[nmp]

That's very interesting, thanks for posting these results.
I was recently thinking about ferricyanide reducer and if it could be useful for the margins of some prints. I have some prints where the border has slight fog because rubylith is not perfect at blocking UV ( i.e. the fog was actually caused by light! ) Maybe I can clean up the margins with a reducer.

Presumably Farmer's reducer is what is called "subtractive" reducer - meaning it will attack the highlights first and then the denser areas. So you can selectively clear up the fog if applied just right. I actually had acquired the chemical to do similar thing with my Centennial POPs where the whites were not coming out white enough because of inadequate opacity of my degatives. You probably have to use much more dilute solution than the 1% I tried with these experiments. I later solved the problem by optimizing the degative color so I never tried using the potassium ferricyanide. It came in handy for this set of experiments.

Thanks for recalling your experiences, by the way. They clearly reinforce the understanding I am developing of the process.