Re: dichromate stain

Though I've not printed gum and have but cursorily read the recent
posts one thing comes to
mind. We have a spa in the backyard. One must monitor it pH-wise
consistently. If not and it
becomes acid it will corrode the copper piping. Recently it was acid
but the water was crystal
clear. Adding soda ash (sodium carbonate) to balance the pH brought out
the vivid blue of copper.

Hence, my assumption is that Clay is on to the problem and it is water.
Water is notoriously hard
in portions of the country and often contains iron. Here in CA I've had
water that virtually is like cotton in that it does not taste wet.

Perhaps all these tests and mixing of chemicals ought to be done
w/distilled water. For instance, if one
wishes to really obtain super clear grain with Tri-X, use Rodinal with
distilled water.

My 2¢

Jack Fulton

Just to throw some more information on the table here, I have
discovered in
conversations with Kerik Kouklis that while we both use virtually
identical
techniques in terms of paper (Fabriano EW), type of gum (B&S) and
amount of
dichromate(saturated Am-Di), sizing (3-4% B&S gelatin) and coating
technique
(rollers), I get dichromate staining and he gets none. Which leads me to
think that the only real difference has to be the water we use for
development.

I know that my water supply here in Houston has quite a bit of iron in
it.
If you allow the tap water to evaporate from a container, a fine film of
hematite (iron oxide) is left behind. I don't know what is in his
water, but
I am betting it is different than mine. Maybe the chemists in the crowd
can
put forward a hypothesis as to why iron rich water would be more likely
to
induce dichromate stain.

The whole subject is only a minor issue to me because I have to be
careful
in evaluating the color of my highlight areas since it picks up a
greenish
tinge from the staining that will disappear when I clear the stain with
potassium bisulfite.
Received on Wed Jun 16 09:35:24 2004