Luis' reply to Dan Shapiro's comment on the strength of dichromates used
with gum caught my interest:
>Not necessarily. You can make a 1% sol. of ammonium dichromate, and a 4%
>sol. of potassium dichromate...
>
>Gotcha!
>
>Luis
I use 2% dichromate (either ammonium or potassium) for gum and other
colloidal printing (except carbon: change of dichromate strength changes
contrast for carbon), including photo-silkscreen, and have always wondered
why everyone else seems to use "saturated" solutions, which come to 13 to
15%. My printing times are quite short, and see no reason to increase the
strength of the sensitizer for speed (2 to 4 minutes with the NUARC).
This relates to the thread a while back on the disposal of dichromate
solutions - since the less you use, the less gets dumped down the sewer
(and the less you have to pay for it). If someone has done controlled
testing and found that more concentration of dichromate contributes to the
process, I'd be very pleased to know.
Would Luis be willing to share with us when he would use "a 1% sol. of
ammonium dichromate, and a 4% sol. of potassium dichromate..." for gum, and
the reason for the difference between the two? Thanks.
Sam Wang
stmwang@hubcap.clemson.edu