[Alt-photo] Re: DAS

[Kees Brandenburg]

Hi Marek, 

The webpage is accessible from here, it might have been a temporary problem. Let me know if you can't. I'll send you the scan off list.

http://polychrome.nl/techlog/apug-group-buy-das

You might try to do a test with an inkjet printed steptablet. Due to the ink dithering it acts like a negative with a stochastic halftone dot. However in my tests with a normal steptablet there is no visible cutoff like you observed. (With digital negatives excellent prints can be made because of the stochastic distributed ink dot these negatives have.

Printing in layers is indeed very nice. Printing higher densities is possible by using thin higher pigmented tissue. The self masking of the sensitizer is an important variable with DAS, that still surprizes me sometimes as an unexpected actor on the scene.... This means that longer exposure are sometimes contraproductive.

Kees



On 1 mei 2013, at 05:46, Marek Matusz <marekmatusz at hotmail.com> wrote:

> Kees, Thanks for the extra work, however I can not get to the website. I did more reading on the two APUG threads and I am coming to a conclusion that what I am seeing is a known and reported property of the carbon printing, known as loss of highlight. I think it is more pronounced with DAS, then with dichromate. Looking at my test strips I would conclude that my dichromate strip is slightly fogged, as the dichromate would perhaps be always somewhat fogged and that's why there is more gradual steps. Also the deeper you print (more penetration of the emulsion) the less pronounced the effect, so I am trying less DAS in the sensitizer. I made some glop with less pigment and it showed more gradual progression as expected, but it is really because of the first step has lower pigment and so the lower density. However this kind of print would require DMAX  of the negative to be above 3, not practical with my setup. That brings me to the other observations that I made by reading the APUG threads. The original ultrastable printing was done with a imagesetter negatives, actually with DMAX at 3 and digital in nature. The final image was also made of 4 LOW density prints (CMYK). I can see how nice low density prints could easily be made with DAS sensitizer. The loss of highlight detail would also be much less visible as 4 different prints would be superimposed resulting in a much smoother progression of tones. I have tried eliminating all the additives and changing pigment sources and all the time I see this loss of highlight detail, kind of pronounced once you get to the full print density. I am really waiting to see your test strips, to see if you could get full print density in one pass.  Marek