A New Cuprotype?

vasya1945 said:

Hi everyone,

I just got chemicals to try this out. What proportions do you recommend to start with?

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I would go by what @fgorga has described in this article:


:Niranjan.

Do I get it right that some staining of whites is inevitable even with extensive washing? My printer is not producing very dense blacks so it is easy for me to blame the printer and transparencies.

vasya1945 said:

Do I get it right that some staining of whites is inevitable even with extensive washing? My printer is not producing very dense blacks so it is easy for me to blame the printer and transparencies.

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In general, yes. The process has an extremely long toe, may be even more than salt prints which has one of the longest out there - so it does require dense negatives. It will also depend on the paper so you could try different papers if you have some - just brush a strip, cover half of it with an opaque material and then process identically. Check the density in the covered up area - that would be the theoretical "chemical/process" staining. Pick the paper that has the lowest. Then test that paper again with a negative with a printed block of 0%B. Look at the density underneath the block. If it is higher than the first test, then the printer is not providing adequate UV opacity. If not then the limitation is chemistry/processing. In that case, you can try what I showed in an earlier post by increasing the thiosulfate content in the recipe.

Having said that, i wouldn't worry too much about staining at this point, particularly if you are not doing a torture test by printing a white border through ink. Within the image itself, if there is a good Dmax-Dmin range, you wouldn't notice it., I suggest you start with the baseline process with the paper of your choice and see where it leads to. Then decide whether it requires any tweaking.

Feel free to share what you come up with.

:Niranjan.

nmp said:

Feel free to share what you come up with.

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Sure, I think it is good to have statistics from inexperied guys. If exposure times won't be prohibitevely long I will do some test and post prints.

I tried exposing test strips and it seems that I cannot achieve good Dmax. Opposite of what I expected. Sensitizer washes away and what is left is very faint. So it is probably paper. I coated three types of paper I have with similair results. I also tested FAC for classical cyanotypes and it works. And papers sort of work for classic cyanotype.

vasya1945 said:

I tried exposing test strips and it seems that I cannot achieve good Dmax. Opposite of what I expected. Sensitizer washes away and what is left is very faint. So it is probably paper. I coated three types of paper I have with similair results. I also tested FAC for classical cyanotypes and it works. And papers sort of work for classic cyanotype.

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At what stage? Dmax at the first stage - expose and wash is not the ultimate Dmax. Cuprous thiosulfate image at that point is light brown. It will get darker red after ferricyanide toning which will further darken after acid treatment.

Please provide pictures.

:Niranjan.

I meant the stage after Ferricianide toning. But I bought other papers and one seems to sort of work. I exposed for 1.5 hours and still there is a difference between naked paper and covered with ohp. Burned area is moderately dark, maybe not as dark as on Frank Gorga's prints but workable. So it is time to do more experiments.

vasya1945 said:

I meant the stage after Ferricianide toning. But I bought other papers and one seems to sort of work. I exposed for 1.5 hours and still there is a difference between naked paper and covered with ohp. Burned area is moderately dark, maybe not as dark as on Frank Gorga's prints but workable. So it is time to do more experiments.

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One of the things about cuprotypes (and cyanotypes as well) that I have found is that for the amount of sensitizer - less is more. If there is too much sensitizer on the paper, most of it stays above the paper topography (if you allow it to puddle for example) forming a crust. Then most of the UV is absorbed by this crust and when developed, the byproduct, cuprous thiosulfate (Prussian blue in cyanotype,) still in colloidal state does not have an anchor to hang on to so it can simply float away. Little or no UV has reached below this crust so the result is a weak Dmax. The trick is to apply enough sensitizer so it fills up the paper fibers but not too much above it. This is going to be highly dependent on the paper - texture, sizing etc. The way I judge is by looking at how long it takes for the coating to dry to matte - a couple to may be 5 minutes are ideal. If it takes longer or if it dries to a shiny surface, good chance there is loss of density because of wash-off.

Tools to moderate this behavior - sensitizer concentration, use of Tween-20, pre-humidifying the paper, use of lower volume of sensitizer per sq inch, brushing off excess sensitizer, drip-dry paper, etc. etc.

:Niranjan.

Wash water is a bit yellow but the amount of sensitizer I apply is small. Less than for cynotypes - 1.5ml for a4 at most (half of which I thinks stays on a brush). I had serious wash off on the first tries but now(with different paper) it is much less. Still dmax is not good. I have two types of paper and one seems to give higher dmax. Also more tween-20 seems to help. But if dmax increases highlight stain increases too. I tried increasing hypo concentration to have 1/0.6 ratio but there is no difference.
On the curious side it looks like that correction curve is not needed. 0-50% zone might be corrected slightly but that's it.
I have attached stepwedge for paper with less staining. Toned in KFeCN an then in citric acid. Compared to cyanotype (right) it is quite pale.
I also had one particularly promising test strip in the beginning with minimal stain but I cannot reporduce it. Not sure what variables have changed.

vasya1945 said:

Wash water is a bit yellow but the amount of sensitizer I apply is small. Less than for cynotypes - 1.5ml for a4 at most (half of which I thinks stays on a brush). I had serious wash off on the first tries but now(with different paper) it is much less. Still dmax is not good. I have two types of paper and one seems to give higher dmax. Also more tween-20 seems to help. But if dmax increases highlight stain increases too. I tried increasing hypo concentration to have 1/0.6 ratio but there is no difference.
On the curious side it looks like that correction curve is not needed. 0-50% zone might be corrected slightly but that's it.
I have attached stepwedge for paper with less staining. Toned in KFeCN an then in citric acid. Compared to cyanotype (right) it is quite pale.
I also had one particularly promising test strip in the beginning with minimal stain but I cannot reporduce it. Not sure what variables have changed.

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That does look rather weak...don't know what to say. Paper is an obvious variable, with everything else being more or less the same. In my experience, the un-buffered papers seemed to give higher Dmax. If you have one of those, like COT320, or Hahnemuhle Platinum Rag, etc. you can try and see if there is improvement.

The other thing that helps with the Dmax is adding copper sulfate to the ferricyanide toner which gives greater density of copper ferricynide than using potassium ferricyanide alone (however the boost of density in the subsequent acid treatment is more muted, higher hypo formula works better in that case.)

You can also replace citric acid with sulfamic acid which in my experiments gave higher Dmax.

Finally, are you exposing it long enough? Is this Sun exposure or you are using an artificial source? You said after 1.5 hours, you still saw difference between OHP and non-OHP areas. Perhaps there is room for improvement there. 1.5 hours is already pretty long, though.

:Niranjan.

nmp said:

like COT320, or Hahnemuhle Platinum Rag

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Maybe you could name a couple more papers? And should I look for cold pressed or hot pressed?

vasya1945 said:

Maybe you could name a couple more papers? And should I look for cold pressed or hot pressed?

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I have not done any expansive paper testing - have only used initially COT 320 and then more thoroughly, Canson XL watercolor paper which is a cold-pressed student paper (as I have detailed in the latter posts in this thread.) Also not knowing what is available where you are, it is hard to make recommendations. Again, @fgorga has done much more work with different papers - see here.

:Niranjan.

The stepwedges I attached are on Canson XL.

vasya1945 said:

Maybe you could name a couple more papers?

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I never tried this particular process, but with other processes I've had good success with papers like Schut Salland 300gsm (50/50 cotton rag/a-cellulose). This is a paper that's available from several shops in The Netherlands (it's also made in NL) and it works well with excellent dmax for several alt. processes. Schut Laurier (100% rag) also works well, but the absorbency of particularly the backside of Salland is quite nice for brush-coated processes, I find. These papers are available per sheet from several art stores and in tubes of 10 sheets and big packs from polymetaal.nl

vasya1945 said:

The stepwedges I attached are on Canson XL.

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Then I am surprised. I used the coarse side of the paper - smoother side has slightly less Dmax, but not by much - not enough to explain your results anyway.

Did you do exposure time test to find minimum time to maximum density, by the way. What source?

Another difference: all my results here on XL were based on sulfamic acid toning, not citric acid. Again the the density boost with SA is not so much as to explain the discrepancy here. But you would get darker prints with it and also move the tone to more neutral. I don't know where you can get sulfamic acid in NL but here in the US, all hardware stores carry it.

If you detail you whole work flow, may be we can figure out better what is going on. Sometimes in alternative processes, small things we might or might not be doing can have an out-sized effect on the outcome.

:Niranjan.

I use @fgorga recipe which I tried both with 10% and 17% hypo solution. My exposure time is 1h15min. I use facial tanner. The exposure time is about when covered and uncovered darks are roughly the same. Tanner gives reasonable times for cyanotypes, something like 20 minutes depending on the distance. Exposure time for cuprotypes can probably be reduced to maybe 50 minutes if I move it closer to the negative.
Today I have tested the last paper I had. Canson Graduate. Unlike most other papers it soaked in sensitizer like crazy, it was wet not even for 20 seconds so I am not even sure I could coat it well. The test print for Graduate is the lowest one and a lower right corner of the frame looks reasonably dark. Upper two are Canson XL with and without citric acid (and I think different sides of paper). For the last one I used quite a bit of polysorbate - 3 drops of 10% solution per ml. If I can reproduce that level of blacks on Graduate I think it is workable. Also you can notice that difference between coverred and uncovered parts. This is because I calibrated exposure for other papers and not Graduate. And the sky is lighter again because I used correction curve for XL.
In reality darks are not extremely dark. Maybe slightly lighter than they look on pictures. I do not have a scanner, this a photo with automatic exposure metering. The stepwedge I posted before might have been slightly overexposed. But still it is clear that compared to cyanotype it is pale.
I use the same 2% solution of KFeCN for all test because I don't have much of it at the moment. I am thinking maybe concentration should be increased.
When doing citric acid toning I noticed that it does not make darks much darker, it is more of shifting hues.
Unwashed exposed prints look quite dense. Then during washing half of this density is washed off, even for Canson Graduate. If it wasn't I think darks would be very good. So maybe I should look for papers that soak more sensitizer.

vasya1945 said:

Unwashed exposed prints look quite dense. Then during washing half of this density is washed off, even for Canson Graduate. If it wasn't I think darks would be very good. So maybe I should look for papers that soak more sensitizer.

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Sorry for my ignoring this thread... sometime life just gets in the way of the important stuff, such as making art!

The passage I have quoted from your latest response suggests to me that this is a paper issue. As @nmp (I think mentioned above) the light sensitive chemistry needs to soak into the fibers of the paper far enough that it does not wash off when processing but not too far so that it cannot absorb light during exposure.

Adding some surfactant (Tween-20) can help with the first problem but it can also make the second problem worse. There is no way to know what works best for a particular paper except by experiment.

When I have similar issues with either a new paper (and a familiar process) or a new process (and a familiar paper), I usually don't bother try and troubleshoot. I simply move on to a different paper.

All of that said, I was unfamiliar with "Canson Graduate" paper and so looked it up. Which paper are using? Canson Graduate seems to be a group of papers two of which (the watercolor and the mixed media) might work and two of which (the sketch paper and the drawing paper) I would not expect to work. The reason I say this is that the first two are designed to work with wet media and thus might have the right balance of absorption properties. The second two papers are designed for dry media (pencil, ink, charcoal, etc.) and are likely to be way to absorbent for alt processes without further treatment (but lets not go there right now!).

The other 'problem' with these papers is that they are inexpensive, beginner papers. Nothing wrong with that but in my experience such papers are not generally suitable for alt process printing. Too many 'shortcuts' and additives used in making inexpensive papers just seem to interfere.

In general, I try to stick with rag papers or papers that have at least 50% cotton content. Such papers are much less problematic with alt process printing.

As for specific papers for cuprotype, Fabriano Unica is my preferred paper for teaching this process, it is an inexpensive 50% cotton paper available in both various size pads (which beginners seem to like) and large sheets (which is my preference).

Other modestly priced 100% cotton papers (at least in the US) include Legion Stonehenge and Lenox 100. (Although I an not sure I have tried the Lenox with cuprotype. I'm not near my prints or notes at the moment.)

As for more expensive papers, I have used Fabriano Artistico and (I think) Rives BFK to make cuprotypes.

That said, I have not done an extensive or systematic survey of papers for cuprotype.

I hope that this is useful information.

--- Frank

P.S. With regard to your question about hot press or cold press... this is a matter or preference. Smooth (hot press) papers are easier to coat (especially if you use a coating rod instead of a brush) and tend to give better details in a photographic print than do textured papers.

vasya1945 said:

I use @fgorga recipe which I tried both with 10% and 17% hypo solution. My exposure time is 1h15min. I use facial tanner. The exposure time is about when covered and uncovered darks are roughly the same. Tanner gives reasonable times for cyanotypes, something like 20 minutes depending on the distance. Exposure time for cuprotypes can probably be reduced to maybe 50 minutes if I move it closer to the negative.
Today I have tested the last paper I had. Canson Graduate. Unlike most other papers it soaked in sensitizer like crazy, it was wet not even for 20 seconds so I am not even sure I could coat it well. The test print for Graduate is the lowest one and a lower right corner of the frame looks reasonably dark. Upper two are Canson XL with and without citric acid (and I think different sides of paper). For the last one I used quite a bit of polysorbate - 3 drops of 10% solution per ml. If I can reproduce that level of blacks on Graduate I think it is workable. Also you can notice that difference between coverred and uncovered parts. This is because I calibrated exposure for other papers and not Graduate. And the sky is lighter again because I used correction curve for XL.
In reality darks are not extremely dark. Maybe slightly lighter than they look on pictures. I do not have a scanner, this a photo with automatic exposure metering. The stepwedge I posted before might have been slightly overexposed. But still it is clear that compared to cyanotype it is pale.
I use the same 2% solution of KFeCN for all test because I don't have much of it at the moment. I am thinking maybe concentration should be increased.
When doing citric acid toning I noticed that it does not make darks much darker, it is more of shifting hues.
Unwashed exposed prints look quite dense. Then during washing half of this density is washed off, even for Canson Graduate. If it wasn't I think darks would be very good. So maybe I should look for papers that soak more sensitizer.

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Actually the 3rd one doesn't look too bad. As @fgorga said, if the paper is too absorbent, and the sensitizer goes too far down in the paper, there is a loss of Dmax as well. That's why there is actually an optimum amount - too much then wash off, too little then not enough conversion. One way to counter the issue of greater absorbency is to increase the concentration of the final sensitizer. In this case, you can increase the solids content of the CuSO4 (from 10%) and/or Na thiosulfate (from 10%,) then adjust the amounts added in ratio of the 50% FAC accordingly. Thicker solution should stay closer to the top and also provide greater reactant spatial density giving rise to higher Dmax. Up to the point when the wash-off mechanism takes over, that is. Of course, you can also stop adding the Tween 20 in such a paper.

The other recommendation I would make is that you can use brushing for ferricyanide toning instead of dip toning if you are short in quantity - with a higher concentration solution, say 20% instead of 2%. But you require a very small quantity even if you apply generously and also, since you would be using it one shot, there is no worry of depleting and replenishing.

Just some additional thoughts.

:Niranjan.

nmp said:

I don't know where you can get sulfamic acid in NL but here in the US, all hardware stores carry it.

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I do t think it's a common hardware item around here, but it's easily available from a number of chemistry suppliers. Try labshop.nl; they carry it.

One more thing about the wash off. When you see that the density is getting reduced drastically as the print is put into water, it is not all because of the good stuff floating away. As I understand, it is also the inherent characteristic of the chemistry itself. Copper complexation with thiosulfate happens in 2 stages - at the first stage, it forms a more soluble product and the second stage results in the insoluble final pigment. The soluble compound also contributes to the print-out density but then it dissolves in development, thus reducing the visual density.

:Niranjan.

koraks said:

I do t think it's a common hardware item around here, but it's easily available from a number of chemistry suppliers. Try labshop.nl; they carry it.

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Many places (hardware stores, building supply store, etc.) won't have a clue if you ask for "sulfamic acid". However if you ask for "brick/masonry cleaner that comes as a solid" they will usually direct you to the appropriate section of the store! Check the ingredients though. Most brands contain only sulfamic acid; a few have other ingredients as well. You want the former.

This section of the store may also sell muriatic acid. This is the common name for concentrated hydrochloric acid (HCl) which also has uses in alt process photography.

Both compounds are strong acids. Sulfamic acid (pKa about 1) is not quite as strong as HCl (pKa about -6). Thus,
in my experience, sulfamic acid often works in place of conc. HCl for many things in the alt process realm. Of course, for each application, the substitution needs to be tested empirically.

The replacement needs to be on a mole for mole basis... i.e taking into account the difference in molecular mass between the two compounds.

@fgorga, point taken, but I was addressing the situation in The Netherlands specifically. Sulfamic acid is not a commonly sold (to the general public) cleaning agent here, certainly not in a pure form. It's similar with e.g. root killer, which I understand is a good source in the US for copper sulfate, but around here it's not common at all as far as I know. This is one of those areas where geographic differences are really massive.

A quick question: is cuprotype sensitive to 395nm light? I know it works for cyanotypes but how about other process? I would like to continue experiments with cuprotypes but I need a powerful light source. Not sure which one to choose.

vasya1945 said:

A quick question: is cuprotype sensitive to 395nm light? I know it works for cyanotypes but how about other process? I would like to continue experiments with cuprotypes but I need a powerful light source. Not sure which one to choose.

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Cuprotype is indeed sensitive to 395 mm light. All iron-based processes (i.e. those using ferric oxalate or ferric ammonium citrate as the light-sensitive component) are sensitive in this range, as are salt prints.

As for UV sources, I use two sets (8 bars total) of "Barrina UV LED Blacklight Bar, 9W 2ft" lights" from Amazon in the US. I assume that something similar is available in the EU. Direct links to Amazon don't seem to be allowed, thus you will need to search there yourself.

These are installed in a homemade box and are about 3 inches (8 cm) above the glass of my printing frame. You can see the inside of my box by looking at post #9 in this thres: https://www.photrio.com/forum/threads/uv-bulbs-burning-out.195848/#post-2621201

Exposure time for cuprotype is 30-40 min. Exposure time for salted-paper (my main process) is 7 min.

fgorga said:

Direct links to Amazon don't seem to be allowed

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They are on Photrio; not sure how Amazon handles deeplinks.