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.
Is this a soak in a tray of dilute acid or can it be applied like the sensitizer and let dry?
Additives, other than carbonate, might also react with acids.
Just another example where empirical knowledge (aka experiments) play a large role in alternative process printing.
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!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 ... agreed.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....
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 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..
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.
...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?
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.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.
All in all, my thinking has always been to avoid acid pre-treament as much as posssible.
:Niranjan.
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.
That's beautiful!Coffee toned cyanotype made with my UV projector,
I was working on printing some Photogravure Intaglios, over the weekend - I have been following Ray Bidegain, a well known photographer/printmaker, and picked up some ideas about ink mixtures - who wants to stay with just plain back. Two from this weekend - not as big as Andrew's - only 7"X9". On Hahnemuhle Durer printed with portland black, sanguine and a touch of umber. The second straight black....
View attachment 407210View attachment 407213
but I'm getting a little tired of the fairly low dmax I'm getting with the process.
The paper definitely stains
- Can you rule out that a negative with a larger density range might not improve this?
- Did you try tannic acid toning?
I wonder if rubbing in wax or something similar onto the print surface to give a bit of gloss to deepen the blacks would work for you.
I'm using a digital UV projector to make these prints and it has way higher dynamic range than needed, I'm also exposing for long enough that the shadows aren't getting any denser. I haven't tried tannic acid toning. What I need to try is either pre-acidifying the paper or using an unbuffered paper like HPR.
I'm currently using Hahnemuhle harmony watercolour paper which I believe is heavily buffered. I'm also using a different cyanotype formula which exposes much faster (important when using a projector) but which produces lower maximum density.
Edit: I'm brushing my toner onto only the image surface, which is why the paper around the perimeter remains properly white. If I bathed the paper it would all end up being the same colour as the highlights. If if didn't done the highlights could easily be paper-white.
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