From: Eric Neilsen (e.neilsen@worldnet.att.net)
Date: 03/27/01-02:12:03 AM Z
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?
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: Monday, March 26, 2001 7:55 PM
Subject: Potassium vs. Ammonium Dichromate (was Re: Clearing Gum Prints)
> Dear Amanda,
>
> Whenever I mix a new gum coating, I make a 4x5" control test print from a
> 'normal' negative of a waterfall (which prints beautifully on Grade 2
silver
> gelatin paper). I also include a Kodak Control Scale T-14, to better
judge
> exposures.
>
> I'm looking at four single-coating test prints, all made with dry-powder
> pigments:
>
> 1. Pigment: Sennelier 'Black for Fresco' 1g/100ml gum + Ammonium
Dichromate
> 30% solution (Mix 1:1)
>
> 2. Pigment: Sennelier 'Black for Fresco' 1g/100ml gum + Potassium
> Dichromate 10% solution (Mix 1:1)
>
> 3. Pigment: Winsor Newton 'Burnt Sienna' 1g/25ml gum + Ammonium Dichromate
> 30% solution (Mix 1:1)
>
> 4. Pigment: Winsor Newton 'Burnt Sienna' 1g/25ml gum + Potassium
Dichromate
> 10% solution (Mix 1:1)
>
> Observations: The color is identical in both cases - the sensitizer used
> does not make a difference. The ammonium dichromate prints are weaker and
> muddy, with less separation between individual steps on the Kodak scale.
> The ammonium dichromate is much faster. An ammonium dichromate exposure
at
> 1.75 minutes is roughly equivalent to a 5 minute potassium dichromate
> exposure.
>
> I use potassium dichromate for the majority of my gum printing. It gives
> cleaner results, stronger separation of tones, and is better suited to my
> enlarged negatives. However, ammonium dichromate is useful, and I do use
it
> in certain situations, e.g. printing a subtle tone into highlights....
> without unduly affecting shadow areas. With the pigments I use, I've
never
> seen color shifts due to use of either sensitizer. However, that's not to
> say the pigment you're using is not reacting to ammonium dichromate in a
> negative way. Is it possible that your prints are overexposed when using
> the stronger sensitizer? What exposure times are you using for AD vs. PD?
>
> Best regards,
> Dave Rose
> Cactus Cowboy
> Big Wonderful Wyoming
>
> > I have been having problems with my coloring. Normally, I use potassium
> > bichromate and notice that the orange color of the chemical has only a
> > slight affect on the overall finished color. However, I recently
switched
> > to using ammonium dichromate and have noticed a very strange reaction
> > with this orange chemical. My colors have been coming out quite
different
> > that one would expect an orange color mixture to produce. I am using
> > Winsor & Newton water colors. Is this color difference normal when using
> > the different chemicals? Why is there such a difference when the
> > chemicals are the same orange hue?
> >
> > Amanda
> >
> >
> >
> >
>
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