Re: Van Dyke Toning
Ken Carney (email@example.com)
Tue, 01 Jul 1997 11:56:32 -0700 (PDT)
A related effect caused a real problem for me a couple of years ago when I began pd printing. For the first few months, I printed under sunlight with good results. On buying a UV source (GE blacklight tubes), I noticed an obvious decline in sharpness. The problem turned out to be a hinged-back print frame. The blacklight is diffuse, compared to the sun (possibly the ultimate point source). Switching to a fixed back frame, and building up layers of paper so that the neg and paper were held very tightly together (the frame is hard to close), fixed the problem. This won't work with the hinged-back frame because it "gives", always leaving a soft spot in the print. You wouldn't think the light source is that critical with a contact print, but it is. When I get time I'll adapt a vacuum frame to the UV box.
> In alt photo everything affect everything else. I too have noticed (and
> measured) an increase in contrast ("snap") in prints exposed by sunlight
> (about 1/6 to 1/3 stops or 0.05 to 0.1 density units in the plat/pallad and
> cyanotype I tested). I doubt this is due to "the old point-source vs
> diffused light situation", as we are contact printing. I would suggest
> that the sun probably has a different spectral "makeup" than UV fluorescent
> tubes. This difference seems (in my case) easily compensated for by
> controlling film development.