Re: gum bichromate

Judy Seigel (jseigel@panix.com)
Tue, 27 Jun 1995 23:43:16 -0400 (EDT)

On Sun, 25 Jun 1995, Adam F. Kimball wrote:
> Alright... All of this discussion of gum printing has gotten into me. I
>
Adam, Sorry I didn't reply sooner, maybe you've reached some
enlightenment by now. If so, please share it.

Because, though the GOOD news is that gum is infinitely seductive,
variable, enchanting, ineffable, bewitching & generally all-around
magical (having focussed on it for several months, I can't imagine going
back to plain old PREDICTABLE mysteries like kallitype!), the BAD news is
that the questions you asked in your earlier note have very few
answers. This is a process in which EVERY variable affects every other
variable, and I know less about it today than I did yesterday. (I mean
that literally; I did some tests this AM which disabused me of certain
gum "truths"!)

That said, I can give you some general suggestions:

First, and this is one of the few absolutes I'll commit to: The
best paper for a beginner (and many advanced printers stick with it) is
Rives BFK. With the right pigment you can give a coat or two without size
(though if you want to re-register you have to pre-shrink, and sizing is
not that much more trouble, though you have to get the formaldehyde.
Gelatine-size plus formaldehyde gives about as good a pre-shrink as you
can get -- contrary to printed info, I find, which always says shrink first.)

Second -- the REALLY bad news is that EVERY pigment behaves differently.
And differently on different paper. And in different weather. Oh, and
also differently from different manufacturers.

You asked me, as I recall, about a nice lamp black. If you find one, let
me know. I've been reading Puyo (with dictionary) -- it's what he used,
in fact all the ancients used lamp black. I'd been printing purple &
majenta & poison green but suddenly felt ready for lamp black. Well, guess
what!
Neither Rowney lamp black nor Winsor Newton lamp black cleared at all on the
5 or 6 papers I tried. (Anyone out there know a good lamp black?) Ivory
black was much weaker, & also didn't clear very well.

The other thing to bear in mind is that you often get one "free shot"
with paper that hasn't been in water yet -- then, the surface size
(presumably) being soaked off, and the nap raised, you're likely to get
staining, at least until you know how to EXACTLY balance
pigment/gum/exposure, and expose promptly, preferably in a temperate-
zone desert.

That dabs-of-paint-pigment-gum-ratio test is, as you
suspected, an absolute waste of time -- unless you do it for each
size/layer/times-in-the-water combination for each paper and even then it's
kind of pointless because by the 2nd, 3rd, 4th, etc. coat, all bets are
off. (Paul Anderson seems to have invented that test, or anyway, was the
first place I read it, reprinted in Henney & Dudley, then in
Crawford .... SEEMS so scientific -- sorry!)

> prints! :) Seriously harsh brushing and high-powered water couldn't break
> through the pigment. It would flake, but it wouldn't clear at all. I

As mentioned, some pigments just won't clear. But also, what about your
drying? In the dark? And what paper? Some papers don't
clear. In fact I had a student
whose prints, it turned out, didn't clear because her size got infected
by a mold in Vermont! I kid you not!

> wondered about the exposure I gave the print, so I printed a step-wedge
> for three minutes under my UV fluroscents- and the same effect. My materials:
>
If you've got optimum light set up (did you do that yet?) one minute is
ballpark exposure. If step wedge didn't clear, it's your paper, pigment,
AMOUNT of pigment, size, or :-) lack of proper humility or sufficient pride.

> Saturated solution of pot. dichromate
> Liquid gum-arabic by Winsor & Newton (I know this stuff is extremely $$$ but
> I had the bug to print RIGHT NOW and I couldn't find anything else.)
> Winsor & Newton Lamp Black tube pigment
> Fabriano Artistico watercolor paper

I suspect that lamp black isn't helping any. Try Rowney (or WN, if you
must) burnt sienna. It's pretty foolproof, and pretty besides.
Or mix Rowney carmine with thalo & some sienna.
I've only used the Fabriano Artistico for VDB & kallitype, where it's
great, but I have a hunch that's another one of your problems (especially
if unsized. Sizing is another whole can of worms -- it behaves
differently with different papers -- but as I recall the Artistico is
pretty absorbent, & just might not release the pigment.)

> I figured I'd start out with Crawfords method so my solutions were combined
>
> 20ml Gum arabic
> 1g pigment
> (thoroughly mixed with pestle)
> 20ml Pot Dichromate (25g:160ml distilled water)
>

I've never weighed pigment -- it's too messy, tiresome & wasteful.
Rather, next time you're on an airplane, liberate one of those little
square plastic desert dishes (or three). Draw an inch-long line inside the
bottom with indelible marker (it has to be redrawn from time to time) &
measure your "worm" of pigment accordingly. Bear in mind that each
pigment has different covering power (thalo much, sepia relatively
little, and lamp black VERY much, for instance) and tube mouths come in
different widths.

Also, why are you mixing so much emulsion at one time? Once mixed, it
won't keep more than an hour -- if that
long. A total of 40 drops (20 drops to a cc) is plenty for an 8x10 print.
(Which is to say, it sounds like you're using unnecessary amounts of
bichromate, which is environmentally undesirable, and pigment, which is
expensive.)

> I coated a number of sheets (all with different amounts of sensitizer) and
> processed them all "automatically" in water around 75 degrees (room temp).
> None of them even looked close to decent.
>

You don't mention how you dried the emulsion. With a hair dryer
perchance? On hot? Dichromate is VERY sensitive to cooking, ESPECIALLY in
summer. Dry paper in the dark with a plain old fan going nearby. And use it
promptly -- as soon as dry in hot, humid weather.

> b) with my pigment:gum proportions
>
No, you're in the ballpark there. You might want to change ratios to
modify contrast or for other artistic reasons when you get to such fine
points, but for now, it's OK.

> c) with Winsor & Newton gum arabic (maybe it is not the 14 degrees Baume'
> as it I though it was)
>
This is in fact a possibility -- the # of degrees Baume isn't such an
issue (there's plenty of leeway, you just adjust proportions of
pigment-sensitizer until it spreads nicely), but someone (member of this
list, in fact) mentioned to me that he had some lithographer's gum that
wouldn't clear ,,, we speculated that it might be the preservative. Just
because it's water white, doesn't mean it hasn't got something mean in
it. I've had students use it, though, and never heard a complaint. But
who knows what they put in it THIS year? That's why it's a good idea to
look in the yellow pages under Lithographers supplies & buy gallon of
lithographer's gum, get the lightest you can find. Yes, maybe it's bad
too (though I've only heard of that the once), but it's about $15 to $20
& if it's OK you've got a 10-year supply. (Another way is to make your
own from powder & add a few drops formaldehyde.)

> Assuming my gum is alright and the paper works, I'll go back into the
> darkroom and do some "dot"-testing to find proper proportions, but if this
> sounds even a little funky to you... let me know before I waste my time
> again.
>

Adam, one of the great beauties of gum bichromate is that it is
absolutely not necessary to do it in the dark -- just DRY it in the dark.
(Unless of course darkroom is only place where you can safely apply
bichromates.) I coat emulsion by roomlight, about 10 feet from
north-facing windows -- just get it in the dark before it starts to dry.
And it seems to me you need a success right now more than you need
"proper proportions" (should there be any such thing!).

Put your gum & dichromate in separate brown glass (preferably) dropper
bottles. Get a tube of burnt sienna, a sheet of Rives BFK, squeeze out 1/2
inch worm, add 2 droppers of gum & mix the paint into it with a smallish
soft round brush (cheap nylon bristles is OK for this which is used only
for mixing, not for developing where you'd want a fine point to pick out
highlights. Brush tiny sample of color-in-gum on scrap of paper (smear it with
finger to see how it fans out, for future reference), add 2 droppers of
bichromate, stir again, dip in 2 or 3 inch foam brush and spread. Now
whisk dry (this is hard to describe, I didn't learn it myself very well
until someone showed me -- maybe we need a video), with a wide cheapo
chinese brush (the 3 dollar kind, not the 23 dollar kind) lightly, like,
one of the Frenchmen says "just whisking the dust off a piano" or like that.
Dry in dark, like I said. Expose.Develop as needed -- from 1/2 hour to 3
days, face down in still water. Fall in love.

Good luck........Judy