From: Christina Z. Anderson (zphoto@montana.net)
Date: 02/23/03-11:52:59 PM Z
Thanks to all who responded to my gum questions, esp those who don't
post much, and keep the info coming! Since I got a couple of people
interested in Demachy's lemon juice and stain test stuff, I'll quote below,
for whatever it is worth. It is interesting to read between the lines, too,
and see what the current argument of that day was at their society. _Photo
Aquatint_ from 1898.
1. Lemon juice: "A strong proportion of citric acid or a smaller
proportion of more active acid added to the mixture of gum and bichromate
will utterly destroy its sensitive properties; that is, will render it
insoluble without exposure to light to such an extent that repeaated
friction with a sponge and hot water will scarcely affect it. We may,
therefore, take advantage of this property to counteract the excessive
solubility of freshly prepared paper and lessen exposure, giving more
stability to the halftones. A small quantity of a weak (say 5 per cent)
solution of citric acid, or simply a few drops of lemon juice added to the
sensitive mixture, will start insolubilisation and allow of slower and surer
development." p.39
2. Stain test: to summarize, pp 31-32, Demachy recommends taking a piece
of coated but not exposed paper and developing it in water as per usual. It
should clear to paper base white. If it does not clear completely, e.g.
there is a stain of the pigment color on there which "can not be removed by
hot water but demands friction with brush or sponge, then the proportion of
gum in the mixture has been too small, the paper has absorbed the pure
colour and is useless for ordinary work..."
Demachy proceeds to say that "paper is always more or less stained by
pure water colour, and that it is the presence of gelatinous gum which
prevents the colour from sinking and allows the total removal of the
pigmented surface, leaving white, unstained paper beneath. This stain will
therefore appear when colour is in excess in relation to proportion of gum,
or when the proportion of colour is adequate to the desired depth of tone
but the quantity of bichromate is too great and has diluted the gum to an
undesirable consistency."
Then Demachy says to take a piece of paper and coat it with bichromated
pigment but no gum and expose and develop, and he says scarcely any color
will wash away, but that with rubbing with cotton wool you will see the
image appear (with pigmented highlights I presume). Then he goes onto other
tests to try for too much coating, etc.
The disagreement during that day was that a guy named Mr. Watsek was
arguing that the proportion of bichromate has no bearing on the exposure,
but instead, exposure was proportionate to greater or lesser gum used. Then
Demachy goes on to say that of course with greater gum the bi is diluted
anyway, so it's not exactly how Watsek thinks it is, etc. etc.
In reading Nadeau's book then, he has Paul Anderson's test quoted in
there, which is similar to Demachy in it doesn't use exposure but it is
different in that it doesn't use any bichromate either, but both seem to be
ways of finding out at what point the gum no longer prevents the pigment
from staying above the paper fibers.
From watercolor experience, there are, of course, many pigments that
cannot be "lifted" with water application--once they're on the paper they
are there, either fully or faintly--depending on pigment type or paper
absorbency. However, you don't use gum arabic while watercoloring usually.
From my watercolor background, too, I would never use alizarin crimson
due to its lack of lightfastness/permanence. I've got Hilary
what'shername's book upstairs with all the descriptions of watercolor
pigments, so I will go thru and check that out, too, but the fact that you,
Katherine, use Hooker's green, and one of your friends uses moonglow (which
is absolutely beautiful in a gum print and I used it often but it seemed to
bleed more, probably due to underexposure on my part) and you question the
chromium rule of thumb makes me believe it is completely all up for grabs
and will require individual pigment testing. Back to the drawing board.
Better to be there than outside where it has plummeted to 26 below!
Chris
----- Original Message -----
From: "Dave Rose" <cactuscowboy@attbi.com>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Sunday, February 23, 2003 5:33 PM
Subject: Re: gum printing
> Greetings from Big Wonderful Wyoming,
>
> ----- Original Message -----
> From: "Christina Z. Anderson" <zphoto@montana.net>
> To: "Alt Photo List" <alt-photo-process-l@sask.usask.ca>
> Sent: Sunday, February 23, 2003 3:17 PM
> Subject: gum printing
>
>
> > Hi List,
> > My usual barrage of questions for the week--but hey, at least I
post
> my
> > test results, too, huh?
> >
> > Gum questions:
> > 1. Which colors absolutely do not work? I have these notes: hooker's
> > green (washes out), emerald green, and any chromium based colors. I've
> loved
> > the quinacridones in the past...moonglow by D Smith seemed to wash out
> quite
> > a bit but could've mixed it up wrong. Do all whites work OK and has
anyone
> > tried a white on a dark paper?
>
> Most of the pigments I use are bought in powder form. Carbon Black from
> Photographers Formulary is a favorite. Ivory or Bone Black is weaker and
> warmer, but works well. I use the earth pigments a lot, Umbers and
Siennas,
> Indian Red, etc... They're an excellent choice for any gum printer.
> Quinacridone is beautiful but weak, as you've noted. Cadmium reds and
> yellows are effective but tend to be more opaque. Phthalocyanine blue and
> green are excellent - great covering power and intense color. I've also
had
> great results with Cobalt blue (cobalt aluminate). I've never used white.
>
> > 2. Do you use am di or pot di? I learned on am di and am wondering if
it
> > is worth it to buy some pot di. Webb/Reed say only use am di if you
can't
> > get pot di. Hirsch says use am di. Go figure. I just want to know
what
> > you guys use, and I do have the notes from the past about am di being
> lower
> > contrast/muddier but then those saying that isn't the case. Does it
boil
> > down to what you are used to?
>
> I use both. Definitely buy some potassium dichromate and try it. Used as
> saturated solutions, AD is faster and prints lower contrast than PD. PD
is
> my choice for most printing. On prints with multiple coatings/exposures
> I'll often use both. PD is good for adding 'punch' into the shadows while
a
> strong exposure with AD (with weak gum/pigment) can produce beautifully
> detailed highlights.
>
> > 2a. If you diluted am di to the same percent as pot di would it be
> > equivalent in speed?
>
> I've never tried it. I use both at maximum strength.
>
> > 3. What clearing agent do you use? I have come across sodium sulfite,
> > sodium bisulfite/metabisulfite, potassium bisulfite, and sulfuric acid
1%
> > solution. Does sodium sulfite truly do the trick so I don't have to
> choke?
> > the metabi literally gives me instant asthma.
>
> Sodium metabisulfite. It is nasty stuff. Best used outdoors on a windy
> day.
>
> Certain pigments and chemicals used in gum printing are hazardous. It's a
> good idea to have a complete file of MSDS sheets and follow all prudent
> safety precautions.
>
> > 4. Has anyone used lemon juice in the sensitizer to insolubilize it,
> > decreasing exposure and giving better midtones? (Demachy,
Photo-Aquatint,
> > p. 39).
> > 5. Dare I ask this, has Demachy's stain test been hashed out on this
list
> > already or is it worth mentioning? His book is from 1898, before Paul
> > Anderson's 1911. Is it possible to talk this out civilly? If he has
not
> > been discussed, I can sum up his test and post it. Considering I've
only
> > been on the list 3 yr or so, you all could have been around this block
> > before.
>
> I'm not familiar with Demachy's "stain test". Please do give us more
> information.
>
> > 6. How many gummists are there? I know Judy, Dave, Katherine, Joe, but
> who
> > else isn't speaking up? Even part-timers?
> > BTW, why I keep asking questions is I am in the starts of
developing
> a
> > "user friendly" alt course as to how I would teach it if given the
chance.
> > I did it with experimental. Now I want to with alt. I've figured out I
> > would "hook" the students first by doing easy enlarged negs (paper,
> > imagesetter, ink jet), start them out with instant gratification cyanos,
> > argyros, (then vdb, kalli, salt) to really get them hooked, then get
into
> > easy one coat gum with spray starch or acrylic sizing, then teach such
> > things as better enlarged negs, better sizing, etc. afterward, before
> > progressing into the more expensive platinum/palladium/zia. The biggest
> > whines I hear is "it's so time consuming, I can't stand gelatin dripping
> all
> > over, I don't have any good large negs, etc." Kinda like the view
> > camera--forget the zone stuff in the beginning, get them out there
fooling
> > around with the camera til they get seduced by the large neg and camera
> > movements, and then go thru the complex stuff. They have to know
"what's
> in
> > it for them" first. My philosophy for the day (of course, 10 processes
in
> > one semester is probably total overload).
> > Chris
>
> I wish you the best of success with your new alt-photo course.
>
> Dave Rose
>
>
>
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