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[fgorga]

Just an FYI regarding paper for Van Dyke Brown printing...

In his book Kallitype, Vandyke Brown and Argyrotype, Don Nelson has a table of 42 papers suitable for VDB printing, only two of these papers require acid pre-treatment before coating.

 

[Raghu Kuvempunagar]

Just an FYI regarding paper for Van Dyke Brown printing...

In his book Kallitype, Vandyke Brown and Argyrotype, Don Nelson has a table of 42 papers suitable for VDB printing, only two of these papers require acid pre-treatment before coating.

Just curious, has this got something to do with the fact that VDB is FAC based whereas the other two processes are not (i.e. citrate vs oxalate)?

Interestingly, Legion Revere Platinum 300 gsm, though a paper made for alt processes and doesn't have buffer, gives better DMax when treated with Sulfamic for all three processes including VDB according to the book.

 

[glbeas]

Is this a soak in a tray of dilute acid or can it be applied like the sensitizer and let dry?

 

[fgorga]

Just curious, has this got something to do with the fact that VDB is FAC based whereas the other two processes are not (i.e. citrate vs oxalate)?

I do not know the answer to this question.

Interestingly, Legion Revere Platinum 300 gsm, though a paper made for alt processes and doesn't have buffer, gives better DMax when treated with Sulfamic for all three processes including VDB according to the book.

My thoughts... even a paper lacking calcium carbonate contains additives (whose identity is proprietary information). Some of these additives might be washed out of the paper upon soaking just in water, especially hot water. Additives, other than carbonate, might also react with acids.

There is no way of knowing what might be going on since we do not know anything about the specific compounds involved.

Just another example where empirical knowledge (aka experiments) play a large role in alternative process printing.

 

[fgorga]

Is this a soak in a tray of dilute acid or can it be applied like the sensitizer and let dry?

Removing carbonate buffer with dilute acid is generally (universally? I don't know anyone who does otherwise) done in a tray followed by washing in water to remove excess acid and the products of neutralization.

Personally, the only exception I make for this is when I treat paper for salt printing with citric acid. I include citric acid in my sensitizer so I just briefly rinse the paper after removing from the citric acid tray. I figure that a little extra citric acid / citrate doesn't make a difference.

My bottom line, these days, is that I use either HPR or Revere Pt for the large majority of my salted-paper or Pt/Pd printing. I don't bother messing with other papers that need acid pre-treatment except if I need/want a special look (most often a warm white paper) for a print. Life is too short.

The exception to the above is cyanotype. In this case I never acid pre-treat any paper. Rather, I 'develop' cyanotypes in a tray of 10-15% vinegar for several minutes before washing them with water. My guess is the the vinegar neutralizes the carbonate before there is significant hydrolysis of the Prussian blue.

 

[Raghu Kuvempunagar]

Additives, other than carbonate, might also react with acids.

Quite possible. If we look at the table of suitable papers in the book Kallitype, Vandyke Brown and Argyrotype, Don Nelson, several papers give poorer DMax after Sulphamic acid treatment (e.g. Bergger Cot 160). In other words, acid pre-soak is not universally beneficial. I guess this is due to some additives reacting with the acid and causing changes that affect DMax in a negative way and also in a process-specific way.

Just another example where empirical knowledge (aka experiments) play a large role in alternative process printing.

Agree.

 

[nmp]

I think one of the things that is underappreciated is what the acid treatment physically does to the paper. Depending on the pH of the acid and the method (dip vs coat) the treatment can also remove the sizing, for example, like gelatin, rendering the paper much more porous. This will change the absorbance of the paper which will affect the Dmax as well, in addition to whatever the difference the chemical change might make.

:Niranjan

 

[NedL]

I think one of the things that is underappreciated is what the acid treatment physically does to the paper. Depending on the pH of the acid and the method (dip vs coat) the treatment can also remove the sizing, for example, like gelatin, rendering the paper much more porous. This will change the absorbance of the paper which will affect the Dmax as well, in addition to whatever the difference the chemical change might make.

:Niranjan

Agree! I've often been unhappy with how the paper texture feels after it dries, even with 2% sulfamic or other acids. With thin papers the corners can become fragile and easier to tear in wet processing. In some of my early paper testing for salt printing, some papers got worse after acid treatment because it allowed the silver to sink into the paper and contact internal sizing... grey blotches visible inside the paper when held up to the light...... I definitely feel like acidification is a 2-edged sword. There was even one canson paper ( I think it was "Canson Edition" ) that got internal grey blotches from the acidification itself! As always, it pays to test first....

 

[fgorga]

I think one of the things that is underappreciated is what the acid treatment physically does to the paper. Depending on the pH of the acid and the method (dip vs coat) the treatment can also remove the sizing, for example, like gelatin, rendering the paper much more porous. This will change the absorbance of the paper which will affect the Dmax as well, in addition to whatever the difference the chemical change might make.

:Niranjan

@nmp ... absolutely!

Agree! I've often been unhappy with how the paper texture feels after it dries, even with 2% sulfamic or other acids. With thin papers the corners can become fragile and easier to tear in wet processing. In some of my early paper testing for salt printing, some papers got worse after acid treatment because it allowed the silver to sink into the paper and contact internal sizing... grey blotches visible inside the paper when held up to the light...... I definitely feel like acidification is a 2-edged sword. There was even one canson paper ( I think it was "Canson Edition" ) that got internal grey blotches from the acidification itself! As always, it pays to test first....

@NedL ... agreed.

My guess/feeling is that strong acids (e.g. sulfamic, hydrochloride, etc.) are more problematic in this regard than weak acids (e.g. citric, acetic, etc.).

The time that paper spends in the acidic solution also probably plays a role. The shorter the exposure the less likely that problems arise.

When I acidify paper, I carefully watch the fizzing on the paper's surface and move the sheets to a tray of water as soon as the fizzing strops.

 

[Raghu Kuvempunagar]

My guess/feeling is that strong acids (e.g. sulfamic, hydrochloride, etc.) are more problematic in this regard than weak acids (e.g. citric, acetic, etc.).

The time that paper spends in the acidic solution also probably plays a role. The shorter the exposure the less likely that problems arise.

In the tests done for the book, Kallitype, Vandyke Brown and Argyrotype, Don Nelson, acidification was done using 10% sulfamic acid for a duration of 10 minutes which was followed by a 30 minutes wash.

In some of my early paper testing for salt printing, some papers got worse after acid treatment because it allowed the silver to sink into the paper and contact internal sizing..

Have you tried starch sizing the paper after acidification as is sometimes recommended for salt printing ? Does it help in preventing some of these troublesome issues?

I think one of the things that is underappreciated is what the acid treatment physically does to the paper. Depending on the pH of the acid and the method (dip vs coat) the treatment can also remove the sizing, for example, like gelatin, rendering the paper much more porous. This will change the absorbance of the paper which will affect the Dmax as well, in addition to whatever the difference the chemical change might make.

Detrimental effect of acidification on sizing is interesting because many papers don't use gelatin size but vegan size like AKD. Is there a significant difference between dip vs coat wrt detrimental effects of acidification?

Some papers are a sorry sight immediately after acidification. Apart from the pores and unevenness, the surface appears less white after acid treatment. One of the Schut papers I tested gave me a heartattack when I acidified it. But after drying it seemed to have healed itself mostly.

 

[nmp]

Detrimental effect of acidification on sizing is interesting because many papers don't use gelatin size but vegan size like AKD. Is there a significant difference between dip vs coat wrt detrimental effects of acidification?

Some papers are a sorry sight immediately after acidification. Apart from the pores and unevenness, the surface appears less white after acid treatment. One of the Schut papers I tested gave me a heartattack when I acidified it. But after drying it seemed to have healed itself mostly.

Yeah, I don't know about AKD sizing. Gelatin solubility is maximum at pH between 4 and 5 (isoelectric point) which is where most of the acid treatments tend to be at. (EDIT: This is obviously wrong! Please see post by @fgorga below how it is so!) I didn't do any coated acid treatment, but in my experiments of weighing the paper before and after dip-treatment with sulfamic acid, it seemed to show far more weight loss than can be explained with just CaCO3 removal alone. Loss of the buffer from the paper by itself will also leave the paper less dense than before, in addition to the loss of other paper additives like sizing. Calcium oxalate is insoluble so oxalic acid treatment keeps the calcium in the paper but then some folks have observed that the paper surface becomes kind of gritty due to crystalline nature of the oxalate. Bill Schwab uses just a coat of oxalic acid, dries the paper and uses it as is without a wash before doing Pt/Pd for papers that are buffered - seeems to work for him. I think citric acid will also remove the buffer but I can't rememeber if I experimented with that.

All in all, my thinking has always been to avoid acid pre-treament as much as posssible. Also, as far as classic cyanotype (and later cuprotype) is concerned, I have never seen a problem with buffered papers. As a matter of fact, the best paper I have found is the Canson XL which is a cheap student paper used without any treatment at all that gave me better Dmax than the COT 320 while keeping the staining to a minimum. I think the buffer helps in FAC based processes acting as a restrainer, just as acid acts as a restrainer for salt prints. The idea of acid pretreatment really started when Mike Ware recommneded it for his New cyanotype which is extremely sensitive to the alkaline enviroment. almost making it unworkable.

:Niranjan.

 

[NedL]

...Have you tried starch sizing the paper after acidification as is sometimes recommended for salt printing ? Does it help in preventing some of these troublesome issues?

Hi Raghu... yes and yes! For salt prints, I tried starch from potato, tapioca, corn, rice, arrowroot, amaranth and some others I'm not remembering of right now. Amaranth has the smallest starch grains but I found it difficult to work with. The most luminous glowing highlights with nice deep darks I ever saw was on a print made with arrowroot starch on acidified paper. With arrowroot, getting the sizing perfectly even is tricky and critical because it just sucks up the salt solution, so any unevenness causes uneven silver chloride density visible on the final print. I always meant to get back to that ( now that I'm retired I don't have an excuse! ) Rice is amazing. Every kind of rice has a different ratio of amylose to amylopectin and they strongly affect the surface absorbancy and barrier characteristics. Strathmore 500 drawing paper is already starch-sized, and does not respond well to acidification, but an additional surface layer of rice starch works great for salt printing. I finally had success with that when I used basmati rice starch which has a lower proportion of amylopectin. All of this probably should be in its own thread somewhere!

 

[fgorga]

Yeah, I don't know about AKD sizing. Gelatin solubility is maximum at pH between 4 and 5 (isoelectric point) which is where most of the acid treatments tend to be at.

This statement is incorrect. Isoelectric point (pI) is the pH at which a protein has a zero net charge. Thus solubility is at a minimum when the pH is near the pI.

Additionally, the pI of gelatin depends on the method by which it is prepared. Gelatin is derived from collagen via hydrolysis. Type A gelatin is made by acid hydrolysis and has a pI of about 5. Type B gelatin is made by alkaline hydrolysis and has a pI of roughly 8.

All in all, my thinking has always been to avoid acid pre-treament as much as posssible.

:Niranjan.

Yes! This is also my thinking. No sense in adding an additional step to my practice when there are many papers that work just fine with out the pre-treatment.

I feel the same way about sizing paper. Early on in my alt process 'voyage' I experimented with starch sizing and decided that I could live with out the added complication.

 

[nmp]

This statement is incorrect. Isoelectric point (pI) is the pH at which a protein has a zero net charge. Thus solubility is at a minimum when the pH is near the pI.

Additionally, the pI of gelatin depends on the method by which it is prepared. Gelatin is derived from collagen via hydrolysis. Type A gelatin is made by acid hydrolysis and has a pI of about 5. Type B gelatin is made by alkaline hydrolysis and has a pI of roughly 8.

Thanks Frank, I stand corrected. You are right of course. (Did I have a brain f..t this morning?) Shouldn't try to sit and write something out of memory without checking. Most papers use the type A, I think. Anyway, what I should have said is sulfamic acid pH is around 1 at 1% concentration that people typically use and at that pH gelatin is very soluble, being quite a bit away from its isoelectric point (I remember seeing U shaped curve for solubility vs pH somewhere but can't find.)

:Niranjan.