Sandy King (sanking@hubcap.clemson.edu)
Tue, 16 Mar 1999 17:33:25 -0400
Luis Nadeau wrote:
>
>>The only exception is when working with negatives of low contrast that
>>require a very dilute sensitizer ( on the order of 1/4 or 1/2%).
>
>I never had any luck with sensitizers that had less then 1.5%. I'd end up
>with blotches, uneven sensitizing, etc., with the regular 2-3 minute
>sensitizing. Do you sensitize for longer periods?
>
>
For reasons which I don't fully understood, but have commented about
previoulsy, in my working conditions I routinely require much weaker
sensitizer than those recommended in most of the literature. This in spite
of the fact that I have worked with a number of different gelatins and
dichromate solutions, and always make tissue and sensitizers with distilled
water. To give you an idea, these are the typical strength sensitizer
needed for negatives of a given density range.
DR .8 - 1.0 1/8%
DR 1.0-1.2 1/4%
DR 1.2-1.5 1/2%
DR 1.5-1.8 1%
DR 1.8-2.2 2%
DR 2.3+ 3% and up
I have not experienced any uneven sensitizing with these very weak
sensitizer, and I don't do anything special. I sensitize by soaking in an
open tray for 2.5 minutes, then squeegee out the excess dichromate
(emulsion side down) on a clean sheet of plate glass, and place the tissue
on a drying rack to dry. Drying is accelerated by directing the air from a
fan a close distance over the surface of the tissue.
I am currently printing with 350na BL fluorescent tubes. For a couple of
years I used GE Daylight tubes, which required an approximate 2X increase
in sensitizer strength to give the same contrast.
Sandy King
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