photogravure problem

Galamndr@aol.com
Mon, 15 Jun 1998 10:59:46 -0400 (EDT)

Recently I have been making some large (16 x 20 and bigger) photogravure
plates and have encountered a vexing problem which never seemed to happen when
I was working smaller: When etching, the center area of the plate always seems
to be a bit behind the rest. This results in what looks like an oval shaped
hot spot, usually most visible in underetched highlights. These hot spots are
not in my positive. I have etched small test plates using the same positive
and have not encountered this problem, but when I go for the full Monty the
problem reappears. My guess is that it has to do with the rate of penetration
of the ferric chloride into the resist and perhaps uneven moisture in the
resist (due to it's large size?) leading to uneven penetration. This is a
particularly frustrating problem (and an expensive one- been going through
alot of copper). Has anyone else out there had a similar problem and/or
suggest a remedy?

Thanks,
Jonathan Higgins