------- Forwarded Message Follows -------
From: Self <CCP/KEITH>
To: "Ronald J. Silvers" <rsilvers@oise.on.ca>
Subject: Re: paper test data for palladium
Reply-to: keith@ccp.arizona.edu
Date: Thu, 15 Feb 1996 22:21:03
Hi Ron,
Sorry for the delay in responding. Our server had been down for a few
days so I'm just now getting to it.
>
> In your Feb 9th reply to Terry King you mention testing palladium with the
> dichromate developer method. I've only used the double solution ferris
> oxolate method for platinum/palladium, but not with the desirable results
> for contrast control that you achieve.
>
> I've got a few questions before trying this developing method of
> controlling contrast. My queries come from reading Dick Arentz's
> description of Phil Davis' method. Dick recommends keeping six bottles of
> developer with different amounts of dichromate in each in order to respond
> to a variation of negative densities. With the double ferris oxolate
> method that I now use, I can create many more than six different mixtures
> for contrast control--supposedly giving greater control than Dick's
> recommendation. I can tailor a mixture to exactly the density range of a
> negative. In spite of this, the double solution method does not give me
> the efficient results I want. Since I work with historical negatives, I'm
> looking for a procedure whereby I can go easily (directly?) from a reading
> of the neg's density range to the right mixture and exposure time. Dick's
> book suggests that I can do so, but there's much "slippage", between a
> density reading and a mixture and exposure time.
I'm not so sure it's even possible to go from reading the density
range of the negative the the proper contrast mixture consistently.
It's not so easy to get an accurate density range from many negatives
in my experience. When I asked Phil about this he just shrugged and
said something about real vs ideal. The problem lies in selecting
what points to read on the negative. Mostly I find my negs have DRs
of about 1.2 according to the densitometer but print as if they were
1.6 to 1.8. Dick's system is based on a shadow density of 90% of
Dmax and a highlight density of 0.04 over Dmin. But how does one
locate such points on a real negative when there is not a spot of
suitable density large enough for the probe to read?
> With your dichromate developer method, do you use more than six mixtures
> (bottles)? Also, do the bottles have to stay in a dark area? Do the
> mixtures of sodium dichromate and potassium oxalate have a limited shelf
> life and exhaustion point? Does it give a different look to the prints?
I have 8 bottles (labelled 0-7) but only have used 0-5 on prints of
actual negatives. #0 is straight potassium oxalate (KOx), #1 is 1
drop sodium dichromate per 200ml KOx, #2 is 2 drops, #3 is 4 drops,
#4 is 8 drops, #5 is 16, #6 is 32, and #7 is 64. According to my
tests of all of these on Cranes Platinotype they are not equally
spaced. Intermediate contrast levels could certainly be obtained.
I replenish in 200ml increments as needed. KOx does not become
exhausted. I don't know about the dichromate. I have found some green
needle-like crystals in one of the bottles. Keep in brown bottles and
away from UV light. Several years ago I kept used KOx in the cloudy
white bottles B&S ships it in and one day found that they had turned
black :-(. I have recently tried to reprint a negative that I 1st
printed last spring using the A:B method (chlorate). The new print is
quite a bit cooler. I'm not yet sure that this can be attributed to
the dichromate or if it may be some other variable (there are so
many) but I am not pleased about it.
> Currently, I'm using Bostick and Sullivan's EDTA clearing. Will this
> work, or do you suggest something else? You mention hydrogen peroxide,
> which I've used before to push contrast. Can it be used for clearing?
> And lastly, I'm wondering, always wondering in using palladium and
> platinum at just how toxic the chemicals are: especially in terms of
> fumes.
I find EDTA not so good with KOx. I prefer phosphoric acid 4% with a
final soak in Kodak HCA. This last realy makes a difference with most
papers. Arches Platine clears best with HCA for all. I've never heard
of hydrogen peroxide as a clearing bath. Others have written to the
list about toxicity. I've never been bothered by fumes from pt/pd
printing but always use adequate ventilation. KOx is very toxic from
what I've read and I never let it touch my skin. Also be very
careful about dust when mixing ferric oxalate from powder.
> Well now, it seems that my concerns do not involve a few, but many
> questions. The thing is, I've not found a publication to provide a more
> detailed description of the dichromate developer method.
>
> with thanks,
>
> Ron Silvers
I hope this helps Ron.
Best wishes,
Keith