Carbon transfer with DAS: poor adhesion and bubbles

[koraks]

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.

 

[nmp]

What's up with the bubbles. Does DAS/gelatin reaction have gaseous by-product? What would happen if you take a dilute solution of gelatin, chuck some DAS and expose to UV. Would bubbles occur then?

Curious...

:Niranjan

 

[Anon Ymous]

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

 

[koraks]

Does DAS/gelatin reaction have gaseous by-product?

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.

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

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]

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.



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.

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

 

[nmp]

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.

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.

 

[koraks]

Bubbles may be the culprit behind delamination though, so the two issues might be related

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.

 

[nmp]

Yeah, it looks like on exposure -N3 of the azide group spits out N2 - hence the bubbles.

https://web.archive.org/web/20190228150554id_/http://pdfs.semanticscholar.org/9412/876dc573872c33ebd594a5821d5397250ea6.pdf

:Niranjan.

 

[revdoc]

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.

 

[koraks]

@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):

If you are only doing single transfer you can soak the tissue in cold water before mating for a while to allow the bubbles to escape off the surface. Using a gloved hand you can run over the surface to try to release the bubbles before mating. Care must be taken not to abrade the image particularly in the lightest toned image areas

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.

 

[sasah zib]

..... It might have been Franck Rondot... I think he also has a video on Youtube where he does this,...

the YT vid

turn on the transcript.

 

[koraks]

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.

 

[koraks]

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.

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

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.