From: Judy Seigel (jseigel@panix.com)
Date: 06/18/03-02:31:34 PM Z
On Mon, 16 Jun 2003, Christina Z. Anderson wrote:
> ...I did get a pH wand so I should
> fiddle with that and test my egg fart gum. Unfortunately, it is mixed with
> powdered pigment (the other colors I have are tube pigment) and I would have
> to mix a whole new batch of pigmented gum to test it side by side and get an
> even remotely usable result.
> How much pH difference was there between the gums? What did you finally
> figure your speed difference was due to? How much speed difference are we
> talking about? Were the gums thicker or thinner and did that contribute?
Christina, I hate to pass up an opportunity to be definitive, but I can
only guess...
Firstly however I did test some 4 or 5 gums with a (OK guys, I may have
the word wrong, it was 5 years ago) hygrometer -- the instrument that
tests density of liquids. I took it to school and used the lab
instrument, a lovely old glass and silver appliance that was beautiful if
not helpful.
All measured 14 degrees baume.
The speed difference varied, and not according to the pH -- from about 3
minutes to full range to 6 minutes -- or in a set time from 3 steps for a
given combo to 6 or 7 steps for the same combo. However, since an
over-exposure can often render more steps with a long soak, there IS NO
SET POINT -- hence the answer can only be relative, not absolute.
In fact, IMO you're asking for absolutes where they CANNOT exist, unless
you make a rule of one paper, one color, one gum, and one development
time, in which case you're throwing away much of gum's magic.
My surmise was that differences in gum source and/or differences in
preservative and/or differences in distilling method and/or difference in
age led to difference in results. But I do not guarantee the same results
with every color. It's probably an interaction. I simply noted it and
adapted. (I use the slowest gum for masking, which I've written about.
I've also noted that some gums stain more with certain sizes and colors
than others. Yes.)
Meanwhile, have I mentioned that this thinking is backwards? For good
gumming you must lose the accustomed "photo mindset." In most alt, and
certainly in gum, you DON'T get the chart in advance and expect the print
to conform. And if it does conform with one combo, as soon as you try a
new brand or new paper or whatever, it may very well disconform (just one
reason why the gum chapter in the Ansel Adams "Guide" was so off the
wall). You test your materials and the given combination and that's "the
chart." Which is to say, you OBSERVE.
I'll add though that it's entirely possible that with all your tools and
zeal, YOU will come up with the answer I didn't. Hope you'll share (tho it
may still not hold across the board). And if you do well with that PH
wand, hope you'll share on that as well. I found it more trouble than it
was worth... though there may be better ones now.
cheers,
Judy
I have only used two gums--Daniel Smith and the one I mixed from powder
> from Daniel Smith and then the Photographer's Formulary powder so I don't
> have any sort of wide experience with gum brands. Oh...no, I did break down
> one time and use that little jar of W+N when I ran out.
> I should clarify that the lemon juice was for insolubilizing the gum,
> or hardening it without exposure, so that there would be "more stability to
> the halftones" (Demachy). It is used to counteract the "excessive
> solubility of freshly prepared paper and lessen exposure..." Lemon juice
> will allow "...slower and surer development..."
> He also talks about insolubilization of the gum occurring without light
> that happens with "..."old gum that has become acid by fermentation". Seems
> both provided him much the same outcome.
> The only thing I can think of is to test this method with a bulletproof
> neg (I have one that has backlit windows in it behind the
> subject--unprintable, really) but even then my puny result will probably be
> anecdotal and end up with the proverbial disclaimer YRMV.
> Chris
>
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