Re: Gum hardening -- top down?

Judy,

So, let me understand. You are able to make gum prints with one
exposure that have both high Dmax (log 1.80 or above as is possible
with carbon), and a complete range of tones from the shadows to the
highlights?

If so, show them, and better, provide working details of how you achieve this.

Or more broadly put, if anyone can do this, show your work and give
the working procedures.

As for your comment, "As for exposure from the back proving top-down
hardening -- surely you jest --do you expect the hardening to occur
on the back of the paper?" I am really left with little to say,
except that this statement proves what an incredibly deficient
understanding you have of the theory, practice and mechanism of
colloid photography.

Finally, you remark, "Meanwhile, FWIW I have tried that exposure from
the back thing for other purposes... After two hours of exposure
NOTHING occurred & I figured the dichromate would harden from old age
-- and me too -- before it "worked," and gave up. So when you say
"very long," you mean about a week?, in which case dark reaction
could be theorized instead..."

The answer to the above is, you need to expose for as long as
necessary. If two hours was not long enough, expose four, or six or
ten or twenty-four hours. I know people who have made beautiful
carbon and gum prints by exposing to a north light for a week or
more. The fact that nothing happened in your experiment proves
nothing.

Before anyone attacks my comments, please bear in mind that I am not
making any claims of superiority as to how to best make gum prints.
My only claim is that the mechanism of hardening is from the top
down. And there are many ways to test this that will demonstrate this
as fact. But people knew this as fact in the middle of the 19th
century, so don't blame me for the bad news.

Sandy

>On Wed, 5 Apr 2006, Sandy King wrote:
>
>>Were there any gum system that would result in hardening of the gum
>>emulsion from the surface of the paper up to the top of the
>>emulsion it would be possible to make gum prints with one coating
>>and exposure that have both high Dmax (log 1.80 or above as is
>>possible with carbon), and a complete range of tones from the
>>shadows to the highlights. No one has ever been able to do that in
>>gum printing, and unless the laws of photochemical reactions are
>>reversed, they never will.
>
>Sandy, shame on you. I won't even talk about my own one-coat gum
>prints (tho you could check P-F # 6), I mention an entire SCHOOL of
>one-coat gum printing, as per Puyo & Demachy, circa 1896. If you
>read French (& I daresay you do) there's an entire literature from
>them on the subject, "Les Procedes d'Art en Photographie," and also
>many English translations (including my own in P-F #1) in which
>Demachy rather snidely refers to "les etrangeres" (meaning the
>Austrian and German school of gum) who require --- eeewww! feh !!!
>-- multi-coat!!! printing!!!
>
>I myself usually prefer the variables possible with many coats, also
>the color changes... AND the EASE ! But the issue here in any event
>isn't top or bottom hardening, it's scale of the coat. Gum doesn't
>readily hold enough pigment to give full D-max & long scale, as the
>bottom tones will block up -- although it will give a full 21 steps
>with a very light pigmenting (or no pigment). So what's that got to
>do with top or bottom?
>
>Which is to say, you can't possibly have tested this before
>asserting your assert. Even so, when you put in enough pigment to
>give good D-max, you CAN get a good scale with savvy handling, the
>right mix, & good balance of exposure and development... Demachy
>used some light water abrasion as well. Others use other devices....
>NONE of which indicates top down exposure, and if you imagine they
>do... ?????? Tut tut.
>
>I don't do carbon printing, but I gather that the gelatin coat in
>carbon is thicker than the gum coat and NOT absorbed into the paper
>the same way. And of course there's the VAST difference in behavior
>between gum and gelatin.. since one of the things this list is so
>splendid at is parsing the nuances of very small differences it's
>surprising that you assume that
>gum and gelatin coats behave the same.
>
>(I'll also add, since the subject came up here last week, that I use
>a relatively THIN coat of gum, that is, thin for a GUM coat, not
>just thinner than a carbon coat. I add water to my gum arabic,
>about a third of the volume, and find the emulsion coats better and
>prints better that way -- probably a a LARGE variable in itself. I'd
>as soon use the thick emulsion described here as attempt to print
>with silicon seal.)
>
>As for exposure from the back proving top-down hardening -- surely
>you jest --do you expect the hardening to occur on the back of the
>paper? If the dichromate is "migrating" to the paper, it doesn't
>know or care which side is "up," it only seeks some kind of
>absorbing or otherwise attracting material.
>
>Meanwhile, FWIW I have tried that exposure from the back thing for
>other purposes... After two hours of exposure NOTHING occurred & I
>figured the dichromate would harden from old age -- and me too --
>before it "worked," and gave up. So when you say "very long," you
>mean about a week?, in which case dark reaction could be theorized
>instead... And it still, given the givens, doesn't prove "top down"
>-- the light comes from the bottom, so in this case the bottom is
>the top, and yet you say it gives a full scale, so maybe it "proves"
>the reverse !?
>
>One other thing hasn't been mentioned.... When the gum coat is too
>thick, it will float off... sometimes possibly in strips. Does that
>prove hardening from the top down, or simply that the coat is too
>thick to expose through. In other words, that circumstances alter
>cases.
>
>Judy
>
>>I have suggested a very simple test that will clearly prove that
>>hardening of a gum emulsion on exposure to UV light is a top to
>>bottom phenomenon, same as it is in carbon printing. Just expose
>>the gum print from the back through the surface of the paper. If
>>you do this you will find that it is possible to get very high Dmax
>>prints with a complete range of tones, though printing times will
>>be very long and some detail will be lost from the texture of the
>>paper.
Received on Wed Apr 5 19:43:00 2006