From: Dave Rose (photo@wir.net)
Date: 03/28/01-11:35:59 PM Z
I suppose it is possible to mix combinations of ammonium dichromate and
potassium dichromate to fine-tune speed and contrast with gum, but I've
never tried it.
I'm not very familiar with platinum printing, but as I understand it, it's a
'one shot' printing, so you'd better get it right the first time because you
only get one chance. In that case, I can see how a fine degree of control
is beneficial, even essential. With gum printing, I'm building layers of
exposures on top of each other. A flat ammonium dichromate exposure will
complement a more contrasty potassium dichromate exposure (in certain
situations). So, given the multiple printing aspect and tremendous
flexibility of the gum process, I've never found the need for a super
precise speed/contrast control when making individual exposures. One of the
beauties of gum is that if your first exposure is too weak/strong or
flat/contrasty you can always compensate with subsequent exposures.
Contrast can also be altered in gum printing by manipulating the gum&pigment
to sensitizer ratio. My normal ratio is 1:1. If I mix 2 parts gum&pigment
to 1 part sensitizer the contrast will be increased. Or if I mix 1 part
gum&pigment to 2 parts sensitizer, the result is lower contrast.
The manipulation and control possible with gum is a fascinating topic. I
could go on and on, but I'll stop here.
Dave Rose
Cactus Cowboy
Powell, Wyoming - population 5,373.....the 15th largest city in Wyoming
(2000 census)
----- Original Message -----
From: "Eric Neilsen" <e.neilsen@worldnet.att.net>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Tuesday, March 27, 2001 1:12 AM
Subject: Re: Potassium vs. Ammonium Dichromate (was Re: Clearing Gum Prints)
> Dave, With platinum printing , one can mix platinum and palladium ( in
all
> their various salts , sodium, ammonium, potassium) to affect color and
> contrast. Have you or can you mix ammonium dichromate and potassium
> dichromate to adjust speed and contrast with gum?
>
> or are your speed changes due to 10% vs. 30% solutions?
certain situations, e.g. printing a subtle tone into highlights....
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