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Carbon transfer with DAS: poor adhesion and bubbles

koraks

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A few days ago I received some DAS from Phototypie.fr
Went ahead and poured some tissues for testing yesterday; this morning the first ones were dry so I could do an initial test. Well, that's not going so well. There are MASSIVE problems with poor tissue adhesion and bubbles. Here's an example:

For scale: the test strip is ca. 2.5" wide.

Details:

Glop recipe for 100ml:
Gelatin: 10g
Pbk7 pigment, aqueous dispersion: 0.1g
Sugar: 3g
Glycerin: ca. 0.2g
DAS (diazostilbene): 0.4g
Tissue poured onto Yupo to a weight height of 0.8 ~ 1.0mm.

The DAS was weighed out and added as a solution in 10ml warm water to the warm glop under red safelight.
Tissues were dried in the dark.

Exposure of the test strip above was 12 minutes for the darkest patch on the right, exposed at 2 minute increments, under a strong 400nm UV light.
After exposure a very clear print-out image is seen for the darkest patches on the dry tissue. Printout image extends further into the weaker patches upon soaking the tissue.

Tissue soaked in tap water (<<20C) for 2 minutes. Millions of bubbles appear. I wiped them off the tissue surface (under water) just before mating with Yupo final support.

Sandwich was allowed to rest for ca. 10-15 minutes. Development in lukewarm water, ca. 41C. After peeling the temporary support away (ca. 4 minutes into development), the lightest patches are still visible, but these wash away pretty soon. The darkest patches immediately show massive bubbles/blisters and many bubbles still present. The lightest patches show no bubbles, but do not adhere well. Note the left-most patch in the example above with partial adhesion.

I re-read the section in King, Nelson & Lockhart on diazo sensitizers and I think I should be doing everything pretty much correctly. The amount of DAS sensitizer is the same as the one listed in the DAS formula on page 135. Otherwise I would suspect that the amount of DAS was below the 'critical mass' mentioned on page 134...if not for the fact that it shouldn't be; I'm right at the 1:25 DAS:gelatin ratio that King et al. recommend as a mininum.

I took a tiny bit of DAS from the container (under red safelight) and examined it under regular room light; it's a dark pink color. Upon exposure to strong UV it darkens to a very deep red, nearly black color. A weak solution of the powder is nearly colorless with a slight tinge of yellow, but turns distinctly yellow upon exposure to UV. Since this is my first experience with DAS, I don't know what the stuff is supposed to look like, but it seems to roughly match the descriptions I've been able to find.

Does the problem ring a bell with anyone who has used DAS before?

With ammonium dichromate I can get perfect transfers every time with the process outlined above, so I'm aware of the basics.
 

Anon Ymous

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I suspect some sort of vacuum pump would be the best solution.
 
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koraks

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nmp said:
Does DAS/gelatin reaction have gaseous by-product?
Click to expand...

The bubbles are apparently notorious with DAS. It even creates bubbles if you just dissolve some DAS in water and expose it to UV! Apparently there are ways to process DAS tissue without the bubbles being an issue, although I'm not the first to observe them.

Frankly, the bubbles are the lesser of the two issues, the poor adhesion being the more puzzling one.

Anon Ymous said:
I suspect some sort of vacuum pump would be the best solution.
Click to expand...

That shouldn't be necessary. Many people do carbon with DAS and don't use a vacuum pump apart from perhaps using a vacuum contact frame, but that's only in the dry part of the process anyway.
 

Anon Ymous

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Ah, if the gas is formed during UV exposure, then a vacuum pump is of no use...
 

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hmm...so it is kind of like FO where CO2 is evloved on exposure. Have to look at the photochemistry behind this.

Bubbles may be the culprit behind delamination though, so the two issues might be related (those big blow outs look like they might be initiated from large bubbles.) They seem to be trapped in the polymer during exposure and only when softened with water they are released. Would more plasticization help in allowing them to diffuse out more effectively during exposure?

:Niranjan.
 
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koraks

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nmp said:
Bubbles may be the culprit behind delamination though, so the two issues might be related
Click to expand...

They might be, but they don't look to be in this case if I look at the low density patch for instance. There were no bubbles here that explain the poor tissue adhesion. I think there are two mechanisms at play here.
 

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Having never used DAS, my knowledge is academic. However, I have read that some users soak the tissue then let it dry to allow the gas to disperse. Then they soak again to mate the final support. This has been mentioned in Sandy's message group by one of the regular posters there. It might have been Franck Rondot... I think he also has a video on Youtube where he does this, but it's been a long time since I watched it.
 
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koraks

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@nmp it is indeed nitrogen, yes.

@revdoc - I don't think many users follow the procedure as you described it and indeed it would make the process much more cumbersome as there would be a second (and quite length) drying time which needs to happen under safelight or in the dark.

For the strip I showed above I happened to have done what Don Nelson suggests here (I wasn't aware of this, but just found it):
But apparently that didn't help enough. Perhaps I just soaked too briefly (2 minutes as per Sandy King's guidelines). I might try again later today.
 
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koraks

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That's interesting, so to prevent (or rather, dissipate) the bubbles, he:
* Soaks the exposed tissue in water, while brushing the bubbles away
* Hang up to dry
* Re-soak (briefly?) and then mate with final support.

Maybe I'll give it a try.
 
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koraks

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So, after a while, I picked up this problem and ultimately resolved it, too.

The solutions I worked out:
1: The bubbles are natural. DAS releases nitrogen gas as it hardens gelatin, and this happens after exposure in the mating bath; see @nmp's post above. I simply brush away the bubbles with a soft foam brush.
2: Exposure unit wavelength matters (!!!) This turned out to be the main problem w.r.t. to the adhesion issues. I had been using my 400nm LED unit and that just doesn't work well with DAS. Going back to a bank of Actinic BL tubes resolved the issue. A combination of both light sources also seems to work just fine.

koraks said:
* Soaks the exposed tissue in water, while brushing the bubbles away
* Hang up to dry
* Re-soak (briefly?) and then mate with final support.
Click to expand...

I also tried this. It's just a waste of time and unnecessary. DAS tissues transfer just fine the same way I do it with dichromate. When transferring to albumen-sized transparency sheets (or Yupo), I do the following:
* Expose tissue. 365nm or shorter wavelength is required for highlight retention.
* Soak for 2 minutes in cold water. Temperature and time are not very critical. Brush away tiny nitrogen bubbles while keeping tissue submerged. When transferring to gelatin-sized paper, soak that until it's completely limp.
* Mate with support. Squeegee.
* Prepare warm water bath and develop print. No wait time is required when transferring to albumen-sized transparencies, acrylic-sized paper, Yupo or glass.

More detailed information including glop recipe and other factors I tested can be found here: https://tinker.koraks.nl/photography/das-right-solving-the-teething-problems-of-das-carbon-transfer/
On this groups.io thread I received some insightful responses: https://groups.io/g/carbon/topic/my_das_sensitized_tissues/96375003

I'm also very grateful to especially Kees Brandenburg for reaching out directly to me and offering very useful advice. He actually confirmed a couple of things I had figured out myself, and dispelled a few common and quite tenacious myths on the transfer procedure. It's all not as finicky as some sources would make you believe.
 

BrendanOrner

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sasah zib said:
the YT vid
turn on the transcript.
Click to expand...

Dumb question to someone new to the technique--in the video to remove the N2 he brushed the soaked tissue and even squeegeed it. Doesn't this affect/damage/misalign the polymerised gelatine i.e. the image itself?
 
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koraks

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No, not in any way; the hardened gelatin matrix is very robust. Even tiny features remain preserved despite this.
Btw, the extended drying time shown in the video is absolutely unnecessary; it really only takes ca. 5 minutes for the N2 to dissipate away. The process is really fairly quick if the tissue has already been made.
 

BrendanOrner

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Thanks that makes sense. (also thanks for your website--it has been super helpful) I've been sensitising with the sodium salt of DAS after making the tissue (with a glass rod) (I just like the idea of being able to optimise the sensitiser concentration on the fly). I'm getting pretty good adherence (I'm sizing with gelatine/potassium alum and pressing for 30 minutes under a metal plate and some very heavy books) and nice details etc (still optimising) but have been running into a) the bubble issue and b) brown staining. I think I'm running into the bubble issue because I'm trying to do really short underwater mating times because I don't like it when the paper and the tissue are slippery against each other and yeah am probably not even waiting the five minutes you suggest (how hydrated the tissue is really should affect the rate of the de-bubbling I'd imagine). I think I might opt for hydrating the tissue post exposure to expel the N2 and then drying again just so I can have a fairly tacky mate. (my paper is 300 g and I'm only doing A5 prints so maybe I wouldn't run into the slipping with larger prints or more floppy paper.)
 
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koraks

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BrendanOrner said:
(I just like the idea of being able to optimise the sensitiser concentration on the fly)
Click to expand...

Contrary to when using dichromate, there's virtually no benefit to this when using DAS. In part it's because it just stops working once you get below a threshold quantity, and in part it's because there's only a marginal effect of DAS concentration on contrast. A third reason is that one of the key advantages of DAS is that you can have 'ready to go' tissue, but this drops away if you sensitize as you do with dichromate.

BrendanOrner said:
I think I'm running into the bubble issue because I'm trying to do really short underwater mating times because I don't like it when the paper and the tissue are slippery against each other
Click to expand...
Okay, but you can split these steps so that you can have a short soak as well as good offgassing. To that end, after exposure, dip your exposed tissue in water. This can be anything between a few seconds up to a few minutes, depending on what works best for you. Currently I mostly use 30-60 seconds.
Then squeegee the tissue on a worktop and cover it so it doesn't receive any additional exposure; if you work in a room free of any UV light, you can just leave it uncovered as well. Wait 5 minutes or so. By this time, the N2 bubbles will be gone.
Now proceed to mate your tissue with the temporary support. This only needs to take a few seconds. If your initial soak of the tissue is short, the tissue won't have absorbed a lot of water and it will not be very slippery. Of course, during mating there is always a thin film of water between the tissue and the support, that you squeegee/roll out between them. During this time you will need to hold them together firmly if you want to maintain alignment. This is inherent to the process. For multi-layer work, you really need to use some kind of registration setup for this with pins through both tissue and support to keep them in place.

BrendanOrner said:
am probably not even waiting the five minutes you suggest (how hydrated the tissue is really should affect the rate of the de-bubbling I'd imagine).
Click to expand...
No, these are different parameters. Your initial soak is independent from the offgassing of the nitrogen, but if you use a long soak, much of the offgassing will happen during the soak. However, it continues as you let the tissue rest after a brief underwater soak. This is where the squeegeeing comes in, as it limits the amount of water that the tissue will absorb.

Too long initial soak times result in a weak tissue that doesn't adhere all too well. But if your process is otherwise solid, you have a pretty decent process window/margin.

BrendanOrner said:
(my paper is 300 g and I'm only doing A5 prints so maybe I wouldn't run into the slipping with larger prints or more floppy paper.)
Click to expand...
Coming back to the problem of the stain: keep in mind that there's really no good way to do a DAS transfer directly to an absorbent paper without stain. The stain is basically impossible to remove. Calvin reports good results with some variants of Hahnemühle inkjet paper that apparently allows the stain to be cleared. Personally I have tried several types of paper and none of them would allow complete removal of the yellow stain afterwards. This is why DAS carbon is usually practiced as a double transfer, where you first transfer to a non-absorbent plastic support (PET or PP film), then clear out the stain, and finally transfer to a gelatin-sized final support.
 

BrendanOrner

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thanks! that clarifies a lot. I'll give your suggestions a try
 
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