Re: Gum Pigments

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From: Christina Z. Anderson (zphoto@montana.net)
Date: 08/02/03-11:54:27 AM Z


Judy,
     Thanks for the long post. I will try to comment on a couple points.

<Judy said>But you apparently haven't understood what's wrong with the
> GPR test -- or for that matter what's wrong with the simpler tests of
> 1905.

Ohhh, yes ma'am I do--I have all posts on pigment stain including your
stain test, and I
understand the issue quite well, and both sides of the issue quite well.
One side says staining is in direct relation to pigment to gum, even whether
dichromate solution is present or absent from the mix (not exposed). You
say
staining is not related to the pigment to gum ratio, in fact, "increasing
pigment has NEVER resulted in staining, staining DID occur when the emulsion
became thin as a result of adding more sensitizer or water" (viscosity
factor), but, in fact,
staining is a result of exposure and dichromate variables (aside from
"sizing, paper, gum, anorexic neg, hair dryer, cheap watercolors" as I quote
from your previous post--posts which I appreciate). This is why, along with
Livick's recommendation, (which, by the way, Scopick ALSO follows--a higher
pigment load in the mix p. 50 "Most gum printers print too pale" or
something to that effect) I started out with a heavy load of 6g/12ml pigment
to gum way back in January of this year. In fact, I have had to back off
that amount for many colors, not because of pigment stain, but because the
color is too brilliant to use at that proportion. That said, I also think
the stain test a la Anderson etc. has validity and I will do it when I get
down to SC and start working with this variable--if Sam will let me test and
not make art :).

> higher authority -- in fact possibly even on this list, ie., Mike Ware.

Higher authority in gum than you, Judy ? :) hehehehehe. Does Ware gum print
on a continual basis? Seriously, though, I really appreciate the info, even
if sometimes inaccurate, of those slugging thru the gum mine fields on a
continual basis.

> The actual chemical reaction for staining needs the exposure and the
> dichromate.

If I remember, Ware said that the hardening of the gum kept the pigment
successfully suspended above the paper, which hardening was less in the
highest highlights, of course, and as you found (which I did, too, as I
mentioned in my posts on lemon juice and gum) that some of your tests
exhibited the highest highlights with more pigment stain, said stain
decreasing toward the midtones, and then so on, to illustrate this point.
I happened to find this result in my step tests only when using lemon juice,
or acid, so I wonder if the acidity of your gum was a factor when you found
this result happen occasionally. Certainly I have no quibble with Ware's
supposing the hardening had an effect on stain.

>
Then, and this was the point of my point:
> those weak coats got into the canon and profoundly affected gum printing.
> (Not to mention that, as I have shown, double the pigment can mean LESS
> staining in an actual print -- see P-F #2, page 46. Ware's explanation for
> that is the increased viscosity.)

Yes, and you're actually quoted in James' book and agreed with.

> He wrote: "I have never experienced the difficulty in getting pure
> highlights *at will* that many gum experts complain of..." (Emphasis in
> original.) He attributes staining to stale gum solution, ie., too acid.

Yes, this actual quote was in my long post quote a week or so ago.
>
<I said>OH, except Demachy in 1898 (does he count?
<Judy asked> Which article/book is that?

Demachy Photo Aquatint, p. 31, I gave you the source offlist a while back.

> I have rechecked my sources, tho it's clearly a waste of time, and I don't
> accuse you of lying, rather of blurring, or misunderstanding the issues.

Nope.

<Judy said> "MOST SOURCES"??? That is definitely not my finding... (as noted
above),
> tho the point is still a detour. My point, bringing all this on, was that
> Anderson's OVERELABORATION of a mistaken "test" changed gum printing from
> a vigorous often one-coat print to a pale and fuzzy look caused by the
> many coats-- leading to the "can't do fine detail" mantra that is in so
> many (tho not all) modern sources, including Keepers of Light, about which
> more before whenever. (And I do not now recall the can't do fine detail
> thing in ANY of the early sources.)

This is an *interesting* observation. I guess the way to test this is to
see if, out of th 80 sources I have notes from, the recommended pigment
concentrations decreased after Anderson's dreaded pigment test.
Unfortunately, since the Germans/Austrians probably are the first to do
multiple coats, I just cannot say that my conclusions would even be valid
unless I could read their sources, which is a real bugaboo. A verrrrry
interesting thesis to pursue, Judy. This is one reason why I chronologized
the 68pp of notes I now have on gum, to see what trends started when and
from whom. It is fascinating.
>
> But wait a minute -- Are you saying that 100% sodium
> dichromate isn't faster than 30% ammonium dichromate? As I recall it was,
> and if sanity fails to return sometime soon, I'll check the file.

Yes, you are correct: Anderson says it is 2x as fast as am di, both at
saturated concentrations. I did not find this true, and that is why I say I
need to do multiple tests again to see if I can continually produce the same
results. Or, let's put it this way: I didn't find sodium dichromate to be
appreciably speedier, if at all, than ammonium dichromate and therefore
worth the use. That's why I asked Sandy King if maybe the thickness of the
syrupy concentrate may be holding back more light than the thinner am di
solution, and maybe that is why I didn't find the saturated solution faster.
Just an academic guess that probably has nothing to do with the price of
eggs. For, we all know that pot di is slower than am di for sure, and those
are the two that are used, usually, if I can breathe that word "usually" in
gum printing. So whatever sodium dichromate does is really only a matter of
personal interest.

Hope that addresses enough in your post, can't wait to see your Anderson
Ripple Effect put into print.
Chris


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