I am looking forward hearing from the DAS group-buyers about their experiences with the magic powder. I am using it also with caseïn now and this works very well! Tonal range looks (a lot) longer that with normal dichromated casein.
Are you referring to caseïn/DAS prints as in an alternative to Gum/Dichromate prints here?
I'm yet to start mine, but before I do I'm also keen to hear of everyone else's experiences.
I'm hoping my negatives will look ok with the longer tonal range (some are 1100mm tall and are very expensive to output)
What is your opinion about the idea of using a spray gun to lay down pigment layers considering the lowered toxicity of Caseïn/DAS emulsion?
Yes I do refer to casein/DAS as a gum/dichromate replacement. Casein printing has a lot in common with gum. With DAS, printing is very straight forward. Developing a DAS/CAS print is ultra fast! My gum negatives are too flat for DAS/casein but that might be corrected by cutting down the casein/DAS ratio. Now I am using a 8% (powdered) casein solution, with 2% ammonium carbonate and 1 gram DAS (1%) per 100ml. This is a higher colloïd/ DAS ratio than I am using in carbon printing. I will test if I can cut that in half and see what that does with the tonal range.
A spray gun might work. It would be interesting to have such a coating option, because brush coating casein is somewhat more difficult than gum. And for both techniques, coating large surfaces is not evident. But be careful, any toxicity of DAS has never been discribed, but this might be due to the fact that there has not been much research in this respect. But with the knowledge we have it would be much much safer than spraying dichromates.
I think it is time to reanimate this old fantastic thread:
Diazo/DAS is also used replace dichromate in Collotype:
The side contains a nice description about Collotype.
For the carbon print: I tried for long time to sensitize coated gelatin layers with a brush. This works in principle even with the Speedball sensitizer. However I always get some degree of fog. (Even on the unexposed parts of the gelatin layer). So I add the DAS now to the gelatin before coating.
Many thanks to Chris for making the DAS available. Since I’ve access to a photo spectrometer I made some absorption spectrum of DAS in water. It has a maximum around 333nm.
Originally Posted by chrisaisenbrey
This is very good news! And your site is very impressive too. Did you observe sensitivety differences or the need to adapt your negatives with DAS compared to dichromate?
And thanks for the spectrometer data.
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Originally Posted by keesbran
The collotype is not my work. (But I would like to try the process) So I don’t know how they have to adapt the process.
For carbon print:
I changed too many parameters to directly compare the results with DAS and dichromate. (I’m still on my way to learn the process of carbon printing)
The sensitivity changes a little but the exposure time is in the range of some minutes with my “face tanner” UV light (~50cm distance).
I have the impression that DAS is working a little softer, but I might be wrong. The gamma can be influenced by the amount of DAS (as reported before) and also by the amount of pigment. I think the gamma should be directly proportional to the amount of pigment. With high amount of pigment it gets of cause difficult to distribute it equally in the glop. (I start with glycerin/pigment/some water and use a glass muller).
For a formula like this:
500mg lamp black (Kremer pigments 47250 Flammruß)
150mg DAS (in 5ml water)
on 17cmx25cm Paper
I get a gamma of 0.7-0.8 on a transparent support. That should lead to a reflective gamma (on a paper support) of about 1.5. So it is in the range of silver-gelatin paper.