[Alt-photo] Re: DAS

[sanking at clemson.edu]

Loris,

The Ultrastable pigment tissue was clearly much thinner than the regular
monochrome carbon tissue I made. As Charles noted, the #100 rod gives a
wet coat height of about .25 mm (250 microns), and this dried down to
about one mil, or 25 microns (0.025"). About a 10:1 ratio.

My tissue has a wet coat height of .09 mm and dries down to about .14 mm,
about a 6:1 ratio. I would normally expect an 8:1 - 10:1 ratio when taking
this measurement so the 6:1 ratio I gave is actually a bit off for me,
possibly because of slightly more solids in the mix.

But in Ultrastable you combine four reliefs to get the final image so the
final image should not be that different in actual thickness.

Sandy







> 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.
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