From: Christina Z. Anderson (zphoto@montana.net)
Date: 07/24/03-08:04:53 AM Z
<Clay said> By
> adding dry dichromate to the gum directly, you can greatly reduce the
> total amount of water in the mix, and increase its viscosity, which can
> lead to some extremely smooth coatings. This may not be something
> desirable for everyone - I don't know. And the point that after the
> layer is dried, and the water has evaporated, it is basically the same
> is also true. But the real benefit, IMO, comes in at the coating stage
> because the viscosity of the solution allows (actually, pretty much
> demands) a different mechanical procedure to be used to lay down the
> coat. I can say with certainty that laying down a layer done this way
> versus using a saturated solution IS different, and it is worth trying.
Two sort of unconnected things:
1. As I pointed out in a long line of posts a while back, Demachy-groupie
as I am, Demachy used a thicker mix of gum, 1 to 1 and 1 to 2 gum to water.
This was found in a number of sources writing ABOUT Demachy as being an
anomaly ("...well, of course, we know that Demachy uses a thicker gum...blah
blah blah"), so one of my quests through the 80 sources I have read to date
(I defy anyone to come up with something on gum I don't have--and if you do,
would you please zerox it for me??) is a comparison of gum dilutions and
figuring out why or when this changed with him and with gum printers to the
more dilute gum we use today (no wonder we have staining--that "s" word).
I think he was achieving the same thing back then that Stuart does now with
adding dry dichromate. It does brush on very creamy and nice, which is the
whole reason I tried it originally--to duplicate Zimmerman's comment that
the coat should go on "creamy". The only way this works without flaking off
I might assume is, as Stuart is doing, to roller on a thin enough coat (yea
Stuart, you go, guy!) , or, as Demachy was doing, to give it a very long
exposure and long development.
2. I would imagine at a certain level of moisture content approaching the
saturation point of dichromate you might have the dichromate precipitating
out of solution, no? And, if using added alcohol, alcohol makes potassium
dichromate precipitate but not ammonium dichromate (Nadeau, 25) so would the
addition of alcohol to the coating solution that I sometimes hear of using
be a detriment?
Stupid academic points that don't make me a better gum printer...but I think
the dialogue on gum we are having on this list this year has actually been
of great benefit to getting closer to the truth about the process....at
least, I've had probably 10 gum myths cleared up in my own mind. So I do so
hope it continues on a positive sharing note!
Chris
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