Re: Waterquality for dichromate sensitizers
Henk Thijs (tys@masadm1.mas.eurocontrol.be)
Mon, 27 Nov 1995 14:15:20 GMT
Stefan wrote:
>..In most photographic processes hard water gives little trouble...
>..In gelatin-bichromate chemistry, however, it is a peril. Firstly
>the swelling power of gelatin is reduced; secondly it affects dichromate
>solutions adversely. It was noticed long ago that a bromoil bleacher made
>up with hard water seemed to lose power after a week or so, with some effects
>on the shadows apparently due to slow interaction between the calcium and
>chromate ions giving rise to general tanning.
>Also, in the carbro process, hard water in the sensitizer has the
>immediately visible effect of eroding the highlights....
In the bromoil literature I found several times the remark concerning hard
water. The danger for contamination and unpredictable results is very high for
bleachers a.s.o. , so the advice would be to use distilled water; for the
soaking afterwards put a teaspoon of CALGON into the water
greetings henk