Re: Gum image has reversed

Hi Bruce,

If I recall correctly Katherine uses a photoflood also but for a max of
around 5 minutes.

Yves

----- Original Message -----
From: "Christina Z. Anderson" <zphoto@montana.net>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Monday, January 09, 2006 12:16 AM
Subject: Re: Gum image has reversed

> Hi Bruce!
>
> Whether the age of my chemistry has any bearing on the
> > results I've experienced, I'm not sure.
>
> Not likely--stuff lasts indefinitely.
>
> >> Lanaquarelle Medium Watercolour 140 lb. Paper, *not* sized
>
> No. 1 advice: size.
>
>
> >> 20 minute exposure
>
> Not familiar with this light source, but under UVBL about 2 inches or less
> away, I get a 6 minute exposure.
>
> >> Emulsion made from 2.5 ml gum, 2.5 ml potassium dichromate solution and
> >> about 0.5 gm Daniel Smith Lamp Black pigment
> >> Still development for about 10 minutes brought up reasonable density --
> >> my fear in letting in go on much longer was that I'd loose the entire
> >> image (just like the first dozen or so failures).
>
> If your fear is to lose the entire image, you are not exposing enough. Is
> your neg dense and contrasty? Lately it has been found that not enough
> exposure has produced reversal of imagery. I found an old quote from back
> 1905 and I love it: 'reversal of an image is caused by underexposure.
Some
> light action is required in every part of the pigmented surface before the
> maximum of solubility is secured." Richards.
>
> This is in line with what both Judy Seigel and Mike Ware have
hypothesized,
> that to prevent pigment staining, some exposure has to occur to harden the
> gum enough to keep the pigment particles suspended off the paper so it
does
> not sink in--that staining is a factor of exposure as well as using too
much
> pigment in your mix. I use very pigmented mixes and don't have staining
nor
> reversal because I size and I expose well enough to allow a development to
> take 1/2 to 1 hour.
>
> I had the reversal experience on unsized paper, too, when I used added
lemon
> juice drops in my mix. The more acid, the more reversal or staining of
> pigment.
>
> > My second question relates to the type of gum arabic I should be using.
> > This success (if you can call a negative print a success) came after I
> > switched back to my old gum arabic powder (25+ years old). The gum was
a
> > fine, white powder which I put into solution using the formula in "The
> > Keepers of Light" by William Crawford. My earlier failures had been
done
> > using some Gum Arabic pre-mixed solution recently purchased from
> > Photographers Formulary. Using the pre-mix I got virtually no
results --
> > anything I got was basically a "soot and chalk" type print where the
> > shadows went black and the highlights blew out. Nothing in between. No
> > detail at all.
>
> I've been using Photo Form gum arabic just fine for the last half year--I
> would suspect your practice is the issue--perhaps a high contrast neg, a
> high contrast use of pot di instead of am di, and not enough exposure are
> all contributing. Soot and chalk I assume is an expression that means no
> halftones? Give it another whirl with a good exposure out in the sun and
> see if your problem doesn't disappear (and then end up with a layer that
> doesn't develop :))
>
> Good luck--great to have another gum aficionado on the list, heheheheh.
> Chris
> >
> > Can anyone explain the lack of results with the pre-mix Gum Arabic?
> > Should I stick with the powdered form and mix it myself? The fact that
I
> > got *some* results from the powder suggests to me that the pre-mix is
> > somehow at the root of my earlier problems where I got soot and chalk.
> >
> > Many thanks in advance -- all advice gratefully received.
> >
> > Bruce Pollock
> >
> >
>
Received on Mon Jan 9 07:26:59 2006