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 Sun Jan 8 23:21:43 2006