[Alt-photo] Re: DAS

[Loris Medici]

Thanks Sandy,

0.14mm dry thickness makes something like 0.14(mm) / 25.4(mm -> in) *
1000(in -> mil) ~= 5.5mil. More than 5x the figure quoted by Charles... I
wonder what's the difference between these practical observations?

Regards,
Loris.


2013/4/18 Sandy King <sanking at clemson.edu>
>
> Bear in mind that how deeply the exposing light can penetrate into a
carbon tissue depends both on pigment loading and the actinic filter of the
dichromate sensitizing agent (which is determined by the concentration). A
thick tissue with very high pigment loading will give a thin carbon relief
that will have no relief. So to optimize final relief it is necessary to
balance the thickness of the gelatin layer and pigment loading so that when
the sensitized tissue is exposed the light is able to penetrate nearly all
of the way to the substrate. Needless to say, the contrast of the exposing
negative must also be carefully matched to the strength of the sensitizer.
>
> In practice my monochrome carbon tissue has a wet coating height of .9mm,
which on dry down measured about .14mm. When this tissue is sensitized with
dichromate solution of the appropriate strength, and then exposed with a
negative of the right contrast range, the exposing light penetrates
virtually all the way the substrate. You can tell this on warm water
development because there is virtually no soluble pigment remaining on the
substrate when it is stripped from the print.
>
> It is possible to make very thin carbon tissue that is so heavily
pigmented that it is not capable of giving any appearance of relief.