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Another idea - do the alkali treatment that reduces the blue but adds yellow ferric hydroxide. Then wash thoroughly to remove any ferrocyanide ions formed as a result. Then immediately treat with oxalic acid (don’t let the paper dry) which will form soluble ferric oxalate with ferric hydroxide. Wash and now you don’t have the yellow in the paper and original cyanotype blue will be back. The highlights will also go back to paper white. It is important to wash the paper before oxalic acid because in presence of ferrocyanide it will convert ferric hydroxide back to Prussian blue.

:Niranjan.
 

Great idea. Would Citric Acid do the same job as Oxalic Acid in your idea? Thinking about other less toxic options, would using Ascorbic Acid instead of Oxalic Acid followed by Peroxide treatment work?
 
As far as the video with the bleaching back that was posted, seems it would just be easier to do it right in the first place. The print in the end looked ok though so whatever works I guess.

I've used Sodium Sulfite to bleach cyanotypes. Works great when you have overdone the exposure a little or if the coating is older so highlights aren't as clean. IIRC I've tried it on heavier prints and past a certain amount of bleaching things start to look off.

Never noticed humidity affecting cyanotype myself but I live where there is almost always humidity. I doubt there is that much difference between low and high for me.
 
Raghu Kuvempunagar said:
When you get a chance, would you mind sharing a pic of this apparatus?
Click to expand...

Raghu, mine is just a length of 1/2" PVC irrigation pipe with 1 inch wide blue painter's tape "shims" set a few inches wider than the paper. The number of wraps of painter's tape can be adjusted for different paper thicknesses and keeps the pipe maybe 1 or 2 mm above the surface of the paper. The pipe never touches the paper, and the PVC is hydrophobic and easy to clean. Easy to move the tape for wider paper or replace if it gets contaminated. I use it with the paper on a sheet of glass. I think people also use something like this for coating emulsions -- it proabably has another name!

Here is Niranjan's description. I think his version has fixed rails as the shims, but it's the same idea. Only liquid ever touches the paper.

I first tried it when I was experimenting with "developing" cyanotypes with pot ferri, but I also tried it on your ferro-blend when I had some smearing. I still got a little smearing just from the motion of the liquid moving across the paper. That was solved by dampening the paper a little before applying the "developer" and after that, a brush worked fine.
 
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Will do. Need to order oxalic acid before it is banned in EU.
Possibly how crucial is humidity control depends on the adopted procedure. I had produced inkjet negatives using EDN (Easy Digital Negative) and was really pleased to see that, as expected, exposing to UV for the same time as the EDN calibration chart resulted in "perfect" cyanotypes. So far I had been drying the sheets (after coating) with a hair dryer. The next day I made duplicate prints, but air-dried instead.
In other words, possibly the various statements about humidity control are all true, but strict control is needed if one relies on a calibrated exposure --instead of test strip just before the print. Just a guess.
 
Raghu Kuvempunagar said:
Great idea. Would Citric Acid do the same job as Oxalic Acid in your idea? Thinking about other less toxic options, would using Ascorbic Acid instead of Oxalic Acid followed by Peroxide treatment work?
Click to expand...

Citric acid will form ferric citrate which is less soluble in water than freshly made ferric oxalate so it will be harder to get rid of. But in principle, yes, it could work. Might have to wash longer. Ferric citrate is orange/red in color so if all of it does not come out, it would probably make the matter worse - colorwise.

Ascorbic acid might work too. Ferric ascorbate is apparently readily soluble in water so is ferrous ascobate. It will reduce ferric ferrocynide of Prussian blue as well. Afterwards, reduced Prussian blue can be oxidized back to Prussian blue with hydrogen peroxide. Or it might revert on its own in the ambient. That's what I observed when doing cyanotype toning of silver. Worth the experiment.

:Niranjan.
 
bernard_L said:
Will do. Need to order oxalic acid before it is banned in EU.
Click to expand...

oxalic acid is a common ingredient in engine flush/radiator cleaner here in the states. You might check around and see if its available as such near you. Its also used as a wood bleach in the fine woodworking trade.
 

Reporting back.
  • Ascorbic acid works. Well. First pic below shows result of 1% ascorbic acid for 30 seconds.
  • That was too strong, too fast. Next time 0.5% or less.
  • A big plus: the color is preserved, in contrast with bleaching with carbonate.
Second stage: hydrogen peroxide. 0.3% solution (3% medical grade, aka "10 volumes", diluted 1+9) for 30 seconds.
  • Just undoes the action of ascorbic acid and reverts to original state.
Thank you Niranjan, this looks like a better way to "reduce" an over-dense cyanotype, while preserving the tonality. Provided one can do just the ascorbic acid step, followed by proper washing. Calling chemists: is that alright?

 
bernard_L said:
Reporting back.
  • Ascorbic acid works. Well. First pic below shows result of 1% ascorbic acid for 30 seconds.
  • That was too strong, too fast. Next time 0.5% or less.
  • A big plus: the color is preserved, in contrast with bleaching with carbonate.
Click to expand...
Good stuff!

I pretty much gave up on toning cyanotypes a long time ago because it seems inevitable to lose paper white highlights. I wonder if this might be a way forward for that problem too. ( I'm wondering if it might regain white highlights after "bleaching" with sodium carbonate, ammonia, or borax. )
 
I am not a chemist by any yardstick, but I think your use of Ascorbic Acid might not be correct. It was meant to be used after a light bleaching with Sodium Carbonate and not by itself. The idea being, you convert some Prussian Blue to yellow Ferric Hydroxide by Carbonate treatment and then remove Ferric Hydroxide by further treatment with Ascorbic Acid. Done this way, you get a print with some density removed while not dulling the print. By skipping Carbonate treatment, you converted Prussian Blue to Prussian White which will no doubt give the appearance of bleaching, but this conversion is temporary. Eventually, or with a Peroxide treatment immediately, all PW will be oxidised to PB and the print gets back its original density.
 
glbeas said:
Can you still get washing borax powder?
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koraks said:
I don't think that was as common in the EU as it was/is in the US. At least not in recent decades. I've never seen it.
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Indeed borax was not a household product here as it may have been in the USA (20-mule team...). More significant, at one of my usual suppliers, I can buy (e.g.) ascorbic acid, tannic acid, polysorbate-20, etc, that were never seen on supermarket shelves; but borax requires proof of professional status. However, a little searching shows that it can be bought from some places as flux for soldering.
 
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Clearly I am much less of a chemist than you. I'm ready to perform more tests.
But, from what I've seen, ascorbic acid will not content itself with just removing (converting to a soluble molecule?) the ferric hydroxide; my simplistic experiment showed it can "reduce" (as in Farmer's reducer, just from the appearance, not presuming the chemical details) directly the blue color of the cyanotype.

Again, what would be wrong with using ascorbic acid by itself as I did? From the visual result, it was effective.
 
bernard_L said:
what would be wrong with using ascorbic acid by itself as I did?
Click to expand...

You found out yourself here.

bernard_L said:
Second stage: hydrogen peroxide. 0.3% solution (3% medical grade, aka "10 volumes", diluted 1+9) for 30 seconds.
  • Just undoes the action of ascorbic acid and reverts to original state.
Click to expand...


bernard_L said:
From the visual result, it was effective.
Click to expand...

I explained what happened and what might happen subsequently.


But if it worked for you, no issues.
 
Raghu Kuvempunagar said:
Eventually, or with a Peroxide treatment immediately, all PW will be oxidised to PB and the print gets back its original density.
Click to expand...
So I missed that part. Sorry about that.

Will make another test during the weekend, and report.

After more careful reading, my understanding is that ascorbic acid has a desired action --to dispose of ferric hydroxide-- and an unwanted side effect --to convert Prussian Blue to Prussian White. The latter --but not the former-- is undone by hydrogen peroxide.
 
Finally starting to get some reasonable results from my PVA-SbQ photopolymer process. Still a lot of work to be done but I appreciate the gritty feel of the current print, at least it works for this subject. 4 layers of pigmented PVA-SbQ (variable pigment load per layer), coated and exposed one-at-a-time and then developed once at the end. Coated on hardened gelatine sized HPR. It's a small print, about 8x10, and I think it would look really nice printed bigger.



This stuff is perfectly suited to exposure via projection. A cyanotype of this size would be about a 30 minute exposure, and this was about 18 seconds (cumulative across all 4 layers). So something like 100 times faster than classic cyanotype. I bet that you could do in-camera exposures with it, but then I don't know how you'd get a good tonal range.
 

Test result below. Left-to-right 1-2-3-4.



  1. New cyanotype sensitizer, 0.8cm3 + 1 drop citric acid 20% + 1 drop PhotoFlo600 1/30. Developed in 1% HCl 2 mins with agitation. Wash ~10min with agitation.
  2. Ditto + 30 s in 1% w/v sodium carbonate. (overcooked?). Wash ~10min with agitation.
  3. Ditto + 30 in 1% w/v ascorbic acid. Wash ~10min with agitation.
  4. Ditto + 3mins in 0.3% hydrogen peroxide.
Notes.
  • Carbonate 1% is too fast acting. Should reduce to 0.5% or 0.2%.
  • Ascorbic acid. I did not reduce the concentration, with the thought that Prussian white must be eliminated and any fading of Prussian blue should be reversed in the next stage. Still difficult to know:
    • How much/long is enough
    • Any adverse effects from doing that stage more than enough
  • Hydrogen peroxide restores (qualitatively) the density resulting from step 2. Also restores some, but not all of the blue color that was present at stage 1.
More work is needed IMO to make this a tool. And, anyone is free to find the tone at stage 2 or 4 (not 3, which I understand is not stable in the presence of atmospheric oxygen) interesting/pleasing.
 

I understand what you are trying to do (I went through a similar excercise some time ago.) However, it is far better to get it right the first time. As you can see, the treatment renders density reduction over the whole range so you are ending up up lower contrast with lower Dmax. That is a tough compromise to make, at least for me.

:Niranjan.
 
nmp said:
However, it is far better to get it right the first time.
Click to expand...
That is also my conclusion. That, or (at least) a test strip for maximum density, assuming the digital negatives themselves are calibrated to a set density range.
Raghu Kuvempunagar said:
That's also what @bernard_L would want to do, but New Cyanotype behaved inconsistently across sessions and hence this exercise.
Click to expand...
I'll strive to be more consistent myself. I must pay more attention to hygrometry. And it seems that the addition of one drop /cm3 of 20% citric, with the paper I use, is adequate only for immediate exposure; otherwise, I may have to look into acidification (sulfamic? I have some left over from the time it was supplied as a de-scaler for kettles).
 
What's the reason behind going with the new cyanotype formula? I haven't tried it myself but also didn't feel it was worth it when I looked at how it's made and read about how picky it is about paper.

Personally I'm still kinda surprised that nobody seems to use the 'blue sheet' formula I found online, as far as I can tell it has a lot of the advantages people are looking for and not many disadvantages. It's simple (exactly the same as classic cyanotype except with potassium ferrocyanide rather than ferricyanide), it exposes 3X faster than classic cyanotype, it gives a really long tonal scale and it doesn't seem to care about buffered paper.

The only downsides are that the print is apparently initially mostly prussian white and it takes a while to oxidise to full density (I assume peroxide could make this happen instantly, but I haven't tried) and possibly the dmax is lower but I don't think by a lot.

When you mix parts A and B together before coating they immediately react and some prussian blue is formed which stains the paper blue as you brush it on (thus 'blue sheet'), however it still works and the blue washes off during development. I've read that with very rough paper the blue coating might not wash out and leave a stain, however I only use hot-press paper anyway which has always cleared fine. I've found the addition of a small amount of citric acid in the first wash water can make the shadows a bit darker, although too much causes bad staining of the highlights. I also add a few drops of tween 20 into the mix before coating to try to get a bit more loading on the paper, but I don't know if this actually helps.

I've even had really good results toning my prints immediately after developing and partial drying without bleaching and without waiting for the pigment to oxidise.
 
AndrewBurns said:
What's the reason behind going with the new cyanotype formula?
Click to expand...
Speaking for myself. When I went into cyanotypes, I had to choose classical or new. Since Mike Ware had apparently a significant expertise on the topic, I followed his recommendation. And, I like the deep blue of New Cyanotype. My sensitizing solution of ten years ago was still OK when I used the last cm3 in the tests posted above.

AndrewBurns said:
Personally I'm still kinda surprised that nobody seems to use the 'blue sheet' formula I found online, as far as I can tell it has a lot of the advantages people are looking for and not many disadvantages.
Click to expand...
Classical, New, Simple; as if that were not enough. How about sharing the make-up, procedure, and results of that "blue sheet" formula?
 
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