CD-POP: Chemically Developed-out Salted Paper Printing Using Vitamin C Developer

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nmp

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The Background:

Developed-out salted paper prints go as far back as 1850’s, credited to Louis Désiré Blanquart-Evrard. Typically it involved a short exposure forming a hint of an image on salted paper followed by development with gallic acid and some silver nitrate to facilitate the physical development.

The main advantage of such a process as opposed to the POP salted paper is that an image can be printed with much lower UV exposure - so at the time there were no artificial sources of UV light, printing could be accomplished on the a cloudy day when it otherwise would take hours of exposure.

More recently, there is a renewed interest among some who would like to make a print directly from an enlarger fitted with a UV source where exposures for a POP salt can be very long. If somehow the times can be cut down, it would be much more viable to go straight from an analogue negative to an enlarged print. This can also perhaps be useful in making in-camera negatives in the same fashion as calotypes, which also involves physical development with gallic acid. Some of these issues were discussed in a thread started by @NedL. There I shared an idea using a Vitamin C developer after removing excess silver nitrate from the paper by washing with distilled water so the development is strictly of the chemical kind and not the physical kind or a combination of both.

Well, that was over 3 years ago and finally I had a chance to try that out. In this particular case, instead of washing out the silver nitrate remaining in the paper as I had suggested then (why waste perfectly good silver,) I treat the paper with 5% NaCl, the same way as one would do in the traditional salt process. What I found is that at that concentration of salt, practically all of the silver chloride formed stays in the paper. There is no wash-out (as confirmed by no action on the affluent with exposure to sunlight or on addition of selenium toner) of any silver chloride as one would see when tap water is used. So now we have a paper with 100% silver chloride, not unlike a silver gelatin paper and a faint image from a short exposure beforehand.

Next comes development with a suitable developer, in this case one containing ascorbic acid or Vitamin C, followed by plain water stop bath, fix, etc – essentially same steps as the salted paper process. As is typical with any new process or for that matter any alternative process one is trying to learn, the challenge is how to get darkest shadows without staining or fogging in the areas that received no exposure and all the tonal variations in-between. After some trial and error, I have found a starter set of exposure time, developer composition/time that gives good whites as well as decent Dmax.

The process is detailed in the next post.


:Niranjan.
 
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nmp

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….continued from Post #1

The Process:

Paper
: Bergger Cot 320

Sensitization:
Salt: 3% NaCl + 7.3% Citric Acid (anhy.) w/w, rod-coat, air dry
Silver: AgNO3 15% w/w, rod-coat, air dry

Exposure:
DIY UV Box using BLB spirals, 5 seconds (compare that with about 12 min required with classic POP salt print under identical chemical makeup)

Salt Treatment:
5% NaCl (Pickling Salt), 6 minutes

Wash:
Tap water, 2 min + 3 min + 4 min

Developer:
Dist water, 750 ml
Add/dissolve: Vitamin C, 10 gm + Sodium Sulfite, 10 gm
Add/Dissolve: Potassium Bicarbonate, 1 gm
Top off: Dist. water to 1000 ml

Working solution = Dilution 1:9, Tap water
Develop time = 10 mins with continuous agitation

Stop Bath and Rinse:
Tap water, 2 min + 3 min + 4 min

Fix:
15% Sod Thiosulfate + 0.2% Na2CO3 + 2% Sod Sulfite, 30 min, One shot

Rinse:
Tap water, 2 min + 5 min

Hypo-Clear:
2% Sod Sulfite + 0.2% Sod Metabisulfite, 10 min

Final Wash:
Static in tray, Tap water 10 min x 4

Next the print.

:Niranjan.
 
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nmp

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….continued from Post #2.

The Print:

CD-POP1.jpg

It’s same digital negative I have used for other processes – originally curve-corrected for commercial POP. The white border is created with ink, not by taping rubilyth or Al foil as a UV barrier so it represents the true level of base fog for the current process/negative combination, which in this case seems to be quite negligible.

The Dmax is quite good too – even better than what I normally get for the straight salt print using this the same initial chemistry and paper. The lighter tones could use some separation – which means this process will need its own optimized curve for the negative. This is one great benefit of digital negative as it can be tailored once the process is fixed not vice versa.

Finally the tone is more neutral than a more reddish untoned salt print.

Compare with the original digital copy of the same image.


Digital original.jpg


:Niranjan.
 
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Herzeleid

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That's quite interesting, it feels part salted paper part chloride emulsion.

What do you expect the shelf life of the developer?

I hope to try this method soon.

Thanks for sharing your experiments Niranjan.

Regards
Serdar
 
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nmp

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That's quite interesting, it feels part salted paper part chloride emulsion.

What do you expect the shelf life of the developer?

I hope to try this method soon.

Thanks for sharing your experiments Niranjan.

Regards
Serdar

Hi, Serdar, nice to hear from you.

About the developer - I initially used Na carbonate as the alkali, with a pH of about 11. That one started turning yellow (sign of oxidation) quite readily - within hours. As a developer, it was also too fast. So I tried to use NaCl as a restrainer to slow it down, with the hope of increasing the contrast as well. It probably would have worked too with the proper combination of dilution, salt concentration and exposure. Then I tried the K bicarbonate, which I happened to have on hand. With the pH just above neutral with that, the developing speed was quite manageable without the need of a restrainer (I generally like to shoot for 5 mins or more) and it seemed to do a much better job discriminating between shadows and unexposed areas. In any case, I am seeing no yellowing in that developer (stock solution) even after about 4 days - still water clear. I am guessing that is related is directly to the stability and efficacy as a reducing agent. Haven't done a time study on it though. Also, I am only using the working solution one shot.

Looking forward to what you can come up with...

:Niranjan.
 

NedL

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Wow, that's fantastic! Well done!
Thanks for following through on this idea.

Agree there should be no excess silver with that much salt.
The long fix is interesting and uses a pretty high concentration of hypo.. the silver particles must be pretty robust ( which would go along with the more neutral color probably? )

Was any faint image visible before development?

I need to pick up some vitamin C and give this a try.
I wonder if we can use sodium bicarbonate as the alkali?
 
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nmp

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Wow, that's fantastic! Well done!
Thanks for following through on this idea.
This is an exception. Usually my follow-throughs are quite lacking....🙂

Agree there should be no excess silver with that much salt.

If there was any silver nitrate left, it would make a stain with a drop of the fixer - which it does not. Kind of like reverse of residual hypo test.

Was any faint image visible before development?

Yes, very faint. First I thought I wasn't going to get anything. Only thing you could see in safe-light was the outer border and very light rocks in the foreground. Development is very slow in the first few minutes visually and then picks up speed halfway. I should have done half regular and half CD-POP, that would have made a nice comparison.

I wonder if we can use sodium bicarbonate as the alkali?

Don't see any reason why it won't. pH's are close. I think the advantage of K is that it is much more soluble, but at the level that is used here, it is well within the limit of Na solubility.


:Niranjan.
 

gone

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Thank you for all the work you put into this, and the detailed and concise way you have spelled everything out.

I prefer the look of the 2nd pic, but they both have their merits. However, I don't actually understand what a digital copy means in this case. Forgive me if I sound dense, I'm actually not, but do you mean that it was a darkroom print that you made a pic of w/ a digital camera? Or a darkroom print that was scanned? Or is it a negative that was inverted in software, and uploaded to the web?

As for liking the 2nd one better, all I have to go by is the image on my laptop. In person it may be a different story.
 
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nmp

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Thank you for all the work you put into this, and the detailed and concise way you have spelled everything out.

I prefer the look of the 2nd pic, but they both have their merits. However, I don't actually understand what a digital copy means in this case. Forgive me if I sound dense, I'm actually not, but do you mean that it was a darkroom print that you made a pic of w/ a digital camera? Or a darkroom print that was scanned? Or is it a negative that was inverted in software, and uploaded to the web?

As for liking the 2nd one better, all I have to go by is the image on my laptop. In person it may be a different story.

Sorry for the confusion...my mistake in not properly clarifying what it was. No wonder you like it better...🙂 - it is original digital picture (actually an old Kodachrome slide I had from the 80's, scanned and Photoshop'd) from which the digital negative was created. I only added it so a comparison could be make in terms of tonal reproduction.

I actually might have a darkroom print from this slide from that time...let me see if I can find a scan of it.

:Niranjan.
 
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nmp

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The long fix is interesting and uses a pretty high concentration of hypo.. the silver particles must be pretty robust ( which would go along with the more neutral color probably? )

The concentration is from O'Reilley's book, except that I added sodium sulfite which supposedly improves its keeping quality.

Earlier when I started back doing some tests on straight salt prints, I wasn't very careful with fixing time (lacking patience) and noticed all of those test strips were brown after a few days in the unexposed areas. Right around that time, Marek Matusz showed data that a long fixing is required to completely remove silver chloride from thicker papers (like 300 gsm or more) which would otherwise stain the paper - particularly accelerated if left out in the Sun. So I did my own study and found that it was indeed true for my process too. My data also corroborated Marek's in that no bleaching occurred with this extended fixing. 30 minutes might be a little bit of an over-kill, but since there is no penalty of any loss of Dmax, I figured it was a safe choice.
Salt Paper Fixing TIme.png

Regarding the more neutral color, yes it is likely related to larger grains, grown as a result of developer action, than in an all-POP process. That would be my first guess, anyway. Although, in the POP process also I have encountered variations - I think moisture plays a big role in the color, among other things.

Speaking of grains, I have a suspicion that this CD-POP process may be more grainy than the straight salt - might be one of its pitfalls, like graininess in a high-speed film. It will be interesting to do a side by side test (within the same coated paper) with a straight salt paper. Exposures times can be another variable playing a role with respect to grain size and tone.

Oh, good....more work!


:Niranjan.
 

NedL

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Hi Niranjan,

That makes sense. I've never used paper as thick as 300gsm and stopped using the "medium" weight paper ( 140 or 160 gsm ) a long time ago. I like thinner papers 90 to about 125 gsm. I can imagine thicker paper would need longer fixing.

I'm looking forward to trying this. I wonder if longer exposure to weaker light would alter the contrast ( that might be something that only happens when there is self-masking in printing out ), or if speed of development matters? I suspect adding some KBr might make it even faster and more neutral.

Cheers!
-Ned
 
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nmp

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I'm looking forward to trying this. I wonder if longer exposure to weaker light would alter the contrast ( that might be something that only happens when there is self-masking in printing out ), or if speed of development matters? I suspect adding some KBr might make it even faster and more neutral.

Cheers!
-Ned

Ball's in your court....🙂
 
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