Carbon Transfer: anyone try Calvin's 'supercoat' tissue concept?

Vaughn said:

How thick is the gelatin of a typical highlight relative to the thickness of the supercoat

Click to expand...

By nature of the carbon transfer process, this question cannot have a discrete answer. But perhaps this is what you mean: if we assume that the tonal threshold fairly consistently occurs at a certain film thickness, the supercoat would have to be slightly thicker than this, but not much more. In this balancing act, erring to the thicker side would be safest. I assume that Calvin's testing has led him to determine a suitable thickness for the supercoat. He coats it to a wet height of 0.5mm, but since the gelatin load is very low (<1%), the dry film size may be something in the order of magnitude of 5-10um. I couldn't say at what specific wet film thickness the tonal threshold typically occurs. I don't even know how fixed this figure is; I have a feeling it might be a fairly narrow bandwidth assuming the process and materials are reasonably tuned.

Vaughn said:

but so glad I am not going in that direction

Click to expand...

It's a choice. Mind you, there are other ways of optimizing highlight rendition with DAS carbon and continuous tone negatives. I find Calvin's approach interesting because I suspect it may be superior, and it's certainly fairly flexible. And I'm of course thankful for Calvin taking an issue seriously that has been downright denied by some of the carbon transfer experts, to my disappointment.

It was sort of a rhetorical question -- just highlighting the significance of the relatively thin supercoat to the thickness of the gelatin in the highlights.

You should have been around (maybe you were) for the old carbon list-serve Sandy King maintained in the 90s. We were constantly re-inventing the wheel, coming up with reasons why something worked or why it didn't. Someone's idea would get shot down, only to re-emerge later as accepted fact...or the other way round. A lot of exploration on the traditional carbon methods of the times.

But the supercoating is a wonder. Why would a clear layer smooth out the transitions between tones in the upper values relative to no layer, as he suggests? Pretty neat, but a wonder.

koraks said:

Indeed; this is one of the tests I'm planning to do.

Click to expand...

Will look foward to seeing your results. In your experience, is the highlight retention issue unique to DAS or is it seen with other Diazo sensitisers as well?

I can't comment on other diazo sensitizers as I've tried none as of yet. I'm also not aware of any that are commonly used or easily available for carbon transfer in particular. On the other hand, it's well-known that all pigment process, also (especially) the direct ones (printmaker's friend etc.) are subject to this effect, regardless of the sensitizer used. The place of the tonal threshold on the tonal scale varies (wildly) with the process and its specific parameters.

The test tissues are ready; I feel I need to have a more suitable test negative as well (in addition to the Stouffer I'll print anyway) so I plan on making one later today. Not sure how far I'll get; planning is a bit uncertain for today.

I was interested in diazo at one point, but the price is crazy high...so, I've stuck with dichromates. Looking forward to your results, @koraks.

koraks said:

I'm also not aware of any that are commonly used or easily available for carbon transfer in particular.

Click to expand...

Andrew O'Neill said:

I was interested in diazo at one point, but the price is crazy high...

Click to expand...

Quoting Sandy King:

"Speedball will work with carbon printing, but shelf life of the tissue will not be as great as with DAS. A number of other Diazonium/diazotype/diazo compounds, including one called Diazon 22LZ (CAS 68988-17-0 (4-Diazodiphenylamine/formaldehyde condensate hydrogen sulfate complex) that I have worked with, have longer shelf life than Speeball and are less expensive than DAS, but shelf life of the tissue is still not as great as that Das sensitized tissue."

Ah yes, it's in their book. I forgot about it since the compound didn't seem to have any particular advantages.

I did some speed testing just now. Unfortunately, that doesn't give me much to work with as it confirms what I recalled about my earlier tests.

I have three gelatins at hand here presently. One is a technical grade, cheapskate porcine gel that stinks to high heaven, has insoluble bits of crud (bone?) in it and that just won't even produce a print at all with DAS sensitization (it just slides off of the support during processing). So that one is out to begin with.

This leaves me with the GMW Photo restoration #2 porcine gel that Calvin recommends for the top coat. It's a great-quality product, very clean, reasonably clear, high bloom/good gel strength etc. I also have a bovine food-grade gel from a wholesale food supplements supplier here. It's also relatively high-bloom, but much more colored than the GMW restoration gel. Otherwise quite comparable. And, as you can tell from the plot above - they're virtually the same speed.

I may have to bite the bullet and get me some of the Photo restoration #1 gel. GMW's shipping costs are a bit on the high side esp. for small quantities, so I've been putting it off. Today I received their catalog (coincidentally?) so I'm going to see if I can bundle some other stuff into my order. Not that I really need anything...ah well.

I did some more testing, but with the same gelatin for both the image forming layer and the supercoat. That evidently doesn't work very well:

Left: tissue without supercoat
Middle: tissue with unsensitized supercoat
Right: tissue with supercoat sensitized with DAS at twice the concentration of the image-forming layer
There's no clear improvement in the tonal threshold behavior as a result of the supercoat under these conditions.

I don't have a pair of gelatins at hand with a one stop innate speed difference, so I'll have to await new suppliers (if I end up ordering them).

Just curious. In your tests did you use the same paper for the final support as Calvin?

These images were never transferred to a final support; the examples you look at are transferred to my default temporary support, which is optimized to yield very consistent and robust transfers.
I forgot to include a link to the blog I took the example above from; it's here: https://tinker.koraks.nl/photograph...et-second-try-with-supercoated-carbon-tissue/
As you can see, there are a few examples of more successful transfers (using tissues of my own formulation that I optimized for highlight performance); they are using the exact same materials as the failed supercoat experiments. So I know that the temporary support I used here works.

At the same time I have also done some tests using inkjet materials, including Hahnemühle Baryta (but glossy, not "Hahnemühle FineArt Pearl*" as Calvin uses), both for single and double transfer. To summarize the findings from several experiments: I don't think that's where the solution is. The inkjet materials have pros & cons (some very serious cons indeed) of their own. I think Calvin uses inkjet media for a single transfer method mostly to demonstrate that the process can be fairly simple and similar to what people are used to in terms of dichromate carbon transfer. He has found a very specific material (the Hahnemühle FineArt Pearl paper he mentions in the video) that works well in terms of DAS stain clearing; in terms of mechanics, there are many materials that work just fine. I could have used something like albumen-subbed Yupo in my examples above and would have gotten the same results.

So the short answer is 'no', but I don't think it's very pertinent.

* This paper is listed at rougly €3 per sheet of A4 in the Hahnemühle shop.

PS, FWIW, here are some examples of inkjet materials I tried:

Left is a generic, fairly heavy RC inkjet paper. This is a direct transfer. Looks OK at first glance, but if you look closely there's yellow stain all over and around the image. Moreover, there are odd wavy marks all over the print that result from idiosyncratic transfer weirdness with this kind of microporous material. Note that the stain on that one is what remains after attempting to remove it for about half an hour and 5-6 consecutive cycles of permanganate/bisulfite clearing. The regular temporary support sheets clear entirely within a single, 2-minute cycle. This same RC print looked like this before I started clearing it:

I eventually gave up trying to clear it; since I left it alone, it seems to have developed some more/new stain...

Middle print in the first image above is a direct transfer to Hahnemühle Baryta FB gloss 350gsm. This paper does not reliably survive warm-water processing; there's a fairly big blister in this print (hard to tell from the photo). Note the heavy DAS stain that's probably embedded in the paper base as well. This will be impossible to clear. This was part of one of my initial supercoat tests; as the example demonstrates, the results were exactly the same as with my regular materials.

The print on the right is a double transfer of an image initially transferred to my standard temporary support and then onto the Hahnemuhle Baryta FB paper. This avoids the staining problem, but as you can tell by the many white marks in the left side of the image, the transfer is incomplete - some bits of the gelatin matrix don't contact well with the Hahnemuhle paper, which really doesn't swell the way a regular gelatin-coated paper does. This results in myriad transfer defects. The temporary support also released with difficulty from the Hahnemuhle paper, and the Hahnemuhle paper is left in a quasi-ferrotyped gloss where the temporary support touched it, which will be a problem if the final image sheet is bigger than the temporary support on which the image is developed; the difference in surface texture will be easily visible.

So lots of problems in that area, not a whole lot of solutions.

koraks said:

These images were never transferred to a final support; the examples you look at are transferred to my default temporary support,

Click to expand...

I must have missed that, my bad.

Incidentally, I came across a post by Calvin that provides interesting insight about supercoat:

"In carbon printing, supercoating emulsions with a very thin layer of unpigmented, but sensitized gelatin has been a goal of mine for many years. The main goal of doing this is to completely eliminate staining, specifically for extended gamut printing. By adding in colors like red, orange, green, or violet, to the standard CMYK gamut, we can print colors that would otherwise be impossible. However, there is a problem with this, most evident in the yellows. Let’s say we add in a violet pigment to increase the gamut in that area. This will work, but in doing so, because the violet layer leaves a small amount of stain, the gamut is reduced everywhere else, especially in the yellows. When working with seven colors, if staining is not controlled, the result can be a muddy mess."

So supercoat is primarily for eliminating staining:

"By supercoating the emulsion with a clear layer of gelatin just a few microns thick, no pigmented gelatin comes into contact with the support, and staining is completely eliminated."

"The clear coat will wash away, or stay attached to the paper, along with the pigmented emulsion, depending on the exposure. The clear coat prevents the pigmented emulsion from coming into contact with the sizing or paper. Therefore preventing all staining, producing brilliant colors and clean whites."

Looks like supercoat isn't as trivial as it seems from a description of its purpose and composition:

"Figuring out how to make that supercoat was the tricky part, but now I have a system that is fairly easy and 95% successful."

With supercoat choice of pigment is broadened:

" since staining isn’t an issue, I can use any pigment I want."

koraks said:

So lots of problems in that area, not a whole lot of solutions.

Click to expand...

Good luck to you with your experiments. Let's hope things will fall in place soon.

Raghu Kuvempunagar said:

I must have missed that, my bad.

Click to expand...

No, it wasn't implied in my post; I should have clarified that bit right away. It was a good question/suggestion, since adhesion issues could very well explain the issues I run into.

Raghu Kuvempunagar said:

So supercoat is primarily for eliminating staining:

Click to expand...

Yes, he mentions this in the video and/or eBook as well. It was also something he emphasized in particular in his writings on gum printing, where staining is even more of an issue.
It's funny/interesting how he speaks specifically of sensitized supercoats here.

Raghu Kuvempunagar said:

Good luck to you with your experiments. Let's hope things will fall in place soon.

Click to expand...

Yeah, although I've not decided yet if I'm going to actively pursue this for now. As shown earlier, I get pretty decent results with my existing approach, but Calvin's idea sounds plausible and at least seems simple enough. If I had had this other gelatin that's required, I definitely would have continued testing.

I was trying to figure out a mechanism that a supercoat could operate by to smooth tonal transitions in the highlights -- reducing the staining sounds like it would be a big part of that.

In his testing in the three years since the old thread above, he seems to be getting away from printing multiple layers in order to simplify the process, yet give people much greater control using digital negatives and non-dichromate sensitizers. Very cool. The added complexity of having to use very specific gelatins from specific sources works against this a bit for now until he can find easily sourced and workable alternates.

I'm not sure if I follow you there, @Vaughn-how do you see the relationship between staining and the tonal threshold issue? I do see that a super coat can help with both, but they seem like different issues to me.

I do agree that the apparent restrictions w.r.t. gelatin choice is a bit of an unfortunate barrier. Calvin does mention the possibility of hydrolizing the image gelatin to make it slower. Maybe that's worth looking into as well, but it of course adds complexity in its own right.

For single transfer prints, wouldn't an unhardened warm gelatin coat on the final transfer at the time of transfer serve the same purpose?

I think that will simply wash off in the warm development bath.

If the staining was as strong as the highlights themselves, that may have an effect of screwing up the tonal relationships in the highlights...it would not be as significant in mid-tones and darker.

Right, I see. Well, when I am talking about the highlight problem, I regard it as distinct from staining. I think it's the same for Calvin.