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

[koraks]

This is a concept Calvin Grier launched recently: you make a regular DAS-sensitized carbon tissue, but you coat a thin layer of clear gelatin on top. This is supposed to help retain delicate highlights, and combat the 'tonal threshold' problem (as Calvin calls it).

Here's the video in which he explains it all:


He's also published an eBook that contains the same material as the video above: https://thewetprint.com/product/carbon-printing-with-inkjet-negatives/
The video is free, the eBook isn't.

I've done my first set of tests, but no luck so far. See my meager results here: https://tinker.koraks.nl/photograph...et-first-test-with-supercoated-carbon-tissue/

I'm honestly also not quite clear on how the concept it supposed to work at a theoretical level. The supercoat is unsensitized, so I don't really see how it's supposed to survive the warm water development step. In my tests, indeed it didn't and most of the image simply slid off the support during development. I'm wondering if others have already tried this (or are willing to dedicate some time to it).

I do not have the correct pair of gelatins for this to work, so perhaps that's why I'm running into trouble with it. IDK; I struggle to see how the unsensitized gelatin layer is supposed to work here.

 

[Raghu Kuvempunagar]

I'm honestly also not quite clear on how the concept it supposed to work at a theoretical level.

Let me hazard a guess. Without the supercoat, the hardened highlight regions of the tissue absorb very little water and don't swell much. When the supercoat is present, because it is not hardened and hence can absorb more water than hardened gelatin, it perhaps helps in increasing the swell of the highlight regions and thereby increasing their contact with the final support.

 

[koraks]

That's an interesting thought @Raghu Kuvempunagar - I had not considered that option. Thinking along the lines of swell, one of the parameters in the process is how long you allow the print to swell before the transfer is made to the final or temporary support. In my experience, longer swell times correlate with adhesion problems, so that would go against what you said here (shorter swell times tend to result in ripple marks).

Other mechanisms I have considered, but not thought through diligently:

• Some of the DAS in the image-forming layer diffuses into the topcoat layer as the latter is coated on top of the (still wet) image-forming layer
• Exposed DAS in the image-forming layer somehow causes hardening in the topcoat layer, perhaps also assisted by some kind of diffusion process. This might occur either during exposure or during soaking of the exposed tissue. If this is part of it, then I'd expect it to occur during the water soak since I assume mobility of molecules in the dry tissue (during exposure) to be severely limited.

I have no proof or credible arguments for any mechanism; at this stage I'm happy to hear about any additional clues, ideas etc.

 

[Raghu Kuvempunagar]

If the idea is to get a very thin layer of unpigmented but hardened gelatin on top of the image making pigmented gelatin, to protect the delicate highlights from washing out during the warm water treatment, then diffusion seems an ungainly mechanism to get precise control. Why not use a lightly sensitised supercoat?

 

[koraks]

Why not use a lightly sensitised supercoat?

My thought exactly, so that's what I intend to try next.

When I first read Calvin's doc & watched the video, I had to check multiple times whether I had not messed a sensitization step for the topcoat - but it really isn't there in his process, to my surprise. I'm sure he must have tested this (he did something similar with gum, years ago), so there's probably a reason why he doesn't do it that way. I guess I'll have to find out the hard way why that is.

 

[Vaughn]

I believe the unsensitized gelatin is just to provide temporary protection the extremely thin highlights during development, keeping the very small amt of pigment in the very thin layer from washing out of the exposed highlights.

I get around this by printing with very low pigments levels that allow for a thicker layer of gelatin in the highlights that resist losing that small amount of pigment. I am also using dichromate and printing from camera negatives which perhaps has less issues.

 

[koraks]

I believe the unsensitized gelatin is just to provide temporary protection the extremely thin highlights during development, keeping the very small amt of pigment in the very thin layer from washing out of the exposed highlights.

So how's that supposed to work without the unsensitized gelatin washing away (as it did in my experiment)? Why would the pigment not wash away from the unsensitized gel (btw, in my experience, it doesn't)?

I'm aware you're using dichromate and thick tissues; both help a lot with highlight retention. The tonal threshold issue is far less problematic with dichromate than it is with DAS. Camera negatives are a mixed blessing since they can in some ways help with highlights, in other ways pose a problem. Esp. pyro-stained negatives are a liability more so than a blessing.
Btw, my work is also predominantly with in-camera negatives.

 

[Vaughn]

It takes time for the small amount of pigment to wash out (diffuse) of that very thin layer of highlight gelatin. A coating of unsensitized gelatin might delay the pigment from washing out in the highlights before the rest of the print can be developed.

We have twoo separate actions happening. Melting the unexposed pigmented gelatin -- and the migration of pigment out of the sensitized, exposed pigmented gelatin. Keep or slow that diffusion from happening and you'll keep your highlight detail.

The other factor is just the highlights being so thin, one can get a mechanical removal of the gelatin (over agitation, etc). A layer of unsensitized gelatin might lend a little physical protection from this happening. This is a lesser issue than the diffusion, I believe.

A third possibility -- a layer of unsensitized gelatin over a layer of sensitized tissue will get partly sensitized from being in contact with the sensitizer in the gelatin below it. This might provide a very thin protective layer over the highlights,.

Pyro negs have been a zero liability for me so far (I use both Pyrocat HD and a non-staining developers)

 

[koraks]

A coating of unsensitized gelatin might delay the pigment from washing out in the highlights before the rest of the print can be developed.

I understand what you're saying, but I think there are several problems with the theory.

A sensitized, exposed gelatin with pigment in it (i.e. the image-forming layer) is more tightly contracted and will release pigment only with severe difficulty. Again, in my work I see very little to no evidence for this happening at any significant scale. An unsensitized gelatin is a much more spacious, flabby matrix and much less capable of trapping something. So the idea of using an unsensitized gelatin to trap a pigment that supposedly diffuses out of a hardened gelatin matrix sounds counterintuitive.

That's not the main problem I have with the theory, though. The main issue is that the implicit assumption is that the tonal threshold problem is created by pigment diffusing out of a gelatin matrix. If you observe affected prints closely (literally closely, microscopically), you'll see that this is not the mechanism at work. The mechanism is very simply the very thin layer of gelatin washing away entirely, taking the pigment along with it. It takes a certain thickness of the matrix to survive the process. This thickness is dependent on several factors, but overall it's significantly larger/thicker for DAS than for gelatin, apparently because the mode of hardening differs between them.

So the solution of trapping diffusing pigment sounds to me like one that belongs to a different kind of problem. Note that what I describe above is consistent with how Calvin explains it in several of his writings and videos, including the ones I linked to in #1. He does not mention pigment diffusion in this context AFAIK.

So that leaves us with the other one, that I do follow:

The other factor is just the highlights being so thin, one can get a mechanical removal of the gelatin (over agitation, etc). A layer of unsensitized gelatin might lend a little physical protection from this happening. This is a lesser issue than the diffusion, I believe.

As pointed out above, we disagree on which one is the lesser issue, but let's step aside that for a moment. With this second theory, which IMO holds much more water, the pressing question I asked in #1 is how an unsensitized layer of gelatin is supposed to help with adhesion. It's unsensitized, therefore it doesn't harden with exposure, and since it sits between the image and the support, as it dissolves, it'll accomplish the opposite from adhesion. This is exactly what my initial experiment demonstrates. So my assumption is that there's something about Calvin's process parameters that makes a fundamental difference. Either it has to do with layer thickness (but I used the same thickness and same gel for the topcoat as he does), or it has something to do with the topcoat not really dissolving away at all. Insofar as Calvin says anything about the mechanisms he believes are at work, it all points towards this unsensitized layer surviving warm water development. It seems to me that for this to happen, it needs to harden. The question is how and when that happens.

A third possibility -- a layer of unsensitized gelatin over a layer of sensitized tissue will get partly sensitized from being in contact with the sensitizer in the gelatin below it. This might provide a very thin protective layer over the highlights,.

Yes, as I said in #3. For me it's reassuring that you arrive at the same conclusion that I did.

Pyro negs have been a zero liability for me so far (I use both Pyrocat HD and a non-staining developers)

Dichromate and DAS are different animals, which is probably why you've not experienced this as an issue. A non-stained negative, especially if it has considerable grain, helps in rendering delicate highlights. It's a bit like printing with a halftone negative, to an extent. That's what I found and documented on my blog some time ago, and interestingly Calvin has included an illustration along similar lines (but without specifically mentioning staining developers, since he talks about inkjet negs primarily) in the e-Book I linked to above. Anyway, I consider the question of staining developers and of the comparison between dichromate and DAS as out of scope of the questions I asked above; they're interesting topics, but I've explored those in depth already and for now don't really have a pressing need to dig deeper into those bits.

 

[revdoc]

At around the 10 minute mark, Calvin explicitly says that the supercoat is a stop faster than the main layer. So it's definitely sensitised.