Re: Potassium vs. Ammonium Dichromate (was Re: Clearing Gum Prints)

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From: Eric Neilsen (e.neilsen@worldnet.att.net)
Date: 03/29/01-09:56:02 AM Z


Dave, It appears that your use of 10% for Potassium Dichromate and that of
30% for ammonium affects speed. What if a 10% solution of ammonium
dichromate were used instead of a solution at 30%? Same speeds? or is the
ammonium still faster at the lower concentration? ( I thought Judy answered
this but I seemed to have deleted her message)

What about sodium dichromate? Does it work and if it does will it produce
more stain, higher or lower contrast?

please go on : )

Eric J. Neilsen
4101 Commerce Street, Suite #9
Dallas, TX 75226
214-827-8301
http://e.neilsen.home.att.net
http://www.ericneilsenphotography.com
----- Original Message -----
From: "Dave Rose" <photo@wir.net>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Wednesday, March 28, 2001 9:35 PM
Subject: Re: Potassium vs. Ammonium Dichromate (was Re: Clearing Gum Prints)

> 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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