Re: Gum and Solutions

<David said>but wouldn't a higher percentage solution
> print slower than a lower precentage for the same reasons that seperate
fast
> film from slow film?
>
Hi David,
     Welcome!
     I'm not getting the analogy between fast and slow film, but with
dichromates, the more you add presumably the faster the gum will harden and
produce a "darker" image. But it doesn't exactly work like that. The
contrast goes down to an unpleasing low, and the increase in speed of
printing with the increase in dichromate amount is, in my GUESS, not what
you would expect as, say, you took D76 and went from a 1:3 dilution to a
full strength dilution to develop your film quicker, or the fact that the
larger grains in a 400 speed film are more light sensitive than the smaller
grains in a 100 speed film.

     Sandy, am I mistaken or haven't you done the step wedge test to
determine what kind of speed change happens with dilution of dichromates?
Kosar (if I dare mention his name) says "Although only very small amounts
(0.5%) of dichromate are necessary for the photochemical hardening of
dichromated colloids, the sensitivity increases almost proportionally with
the dichromate concentration." Scientifically this may be so, but
practically do you find this to be the case? Or does it follow some sort of
shouldered curve?
Chris
Received on Sun Nov 23 10:06:47 2003