Re: gum control

Judy Seigel (jseigel@panix.com)
Thu, 30 Jan 1997 14:27:22 -0500 (EST)

On Wed, 29 Jan 1997, Terry King wrote:
> With the more highly reflective colours, eg yellows, you need more
pigment
> to get contrast but more pigment decreases the effectiveness of the light.
> In general strong pigments, where you need less of it to achieve the same
> effect, will be of benefit.

Terry, I'm not insisting that you take a Trappist vow of silence, far from
it, but you are simply wrong in this.

I mean not just wrong in confusing "contrast" with chroma, and both
with covering power, but wrong....

For instance 5 different yellows seen on the paper have the same quality
of what you call "reflectivity." Their *covering power* and hence the
amounts of each needed to get that color in a print varies widely. The
covering power of arylide yellow, for instance, is greater gram for gram,
not simply than many other yellows, but for all its "reflecctivity"
greater than either thalo blue or quinacridone red. This is seen in the
fact that smaller weights of the yellow are needed to balance tricolor
gum. I say this with confidence because I have weighed the pigments.

Weighing pigment, I must add, is hardly more effort than squeezing alone.

Put a little plastic airline desert dish on the pan of the scale. (Mine is
Alaska airlines, weighing 24 grams). Start with the marker balanced at
this weight. Then slide marker up to add the amount of pigment you want,
squeeze paint into the dish until the needle again balances. Add the rest
of ingredients as usual. Dish is wide enough to take the foam applicator.
No waste, as there is inevitably in trying to lick emulsion off a plate
with a brush.

But again, speaking of "reflectivity", so called, of paint, we might feel
that various blues -- prussian, indigo, ultramarine, permanent, thalo,
etc. -- "reflect" light similarly, but they are vastly different in
covering power. Indigo, for instance, would take a fraction of the bulk of
some of the others, as you well know (especially as you sent me to
indigo).

> There is an aternative approach that can give more information, in the
> context of the multicolour print, and that is making a work print stage by
> stage in advance of making the final print.

Hello? Would you please explain the difference between that and making a
gum print? I mean every multicolour print advances stage by stage.
Sometimes there are false starts, and sometimes great discoveries, but
doing the same thing twice would be as boring as...... platinum printing?

> funnily enough, Gloy/ammonium dichromate
> seems to be about three times as fast.as potassium dichromate/gum arabic.
> At least it was when I had to scour a town for materials after a college
> pleaded that its gum arabic and potassium dichrmate had not been delivered
> for my workshop. My demonstration with the, then absolutely new to me,
> Gloy/ammonium dichromate grossly over exposed compared with my usual
> practice. I had to reduce the exposures to about a third before the
> combination would work.

My tests showed speed of gloy to be about the same as for gum. I'd say the
speed change you describe above was due to the ammonium dichromate, not
the gloy.(You changed 2 variables at once & leapt to an assumption.) In
any event, I doubt speeds of the kind we're talking about matter so much.
My friend's problem was *30* minutes, another order of magnitude entirely.

The am di is faster, for reasons not entirely clear, as I noted in my
last... But I notice that your reducing exposures to a third is in terms
of *time* of exposure. I was thinking more in terms of *steps* on the
21-step or stops -- that reciprocity isn't clear to me. Nor does it
matter either, tho I once had an actuary in a workshop who demanded to
know it & didn't think much of me when I couldn't supply it. (I should
have made one up & told him he put in too much/too little pigment.)

> One recent
> addition to the armoury has been the soft spongy dish cloth which is
> marvellous for bringing out additional detail.

My best addition was yesterday -- a friend gave me a FAT little syringe,
which proved perfect for directing a light gentle stream of *perfectly
aimed* water. I've used everything, from turkey basters to eye droppers,
to watering cans. I've used mammoth syringes and baby syringes, none of
which did it. This one worked miracles, perfectly delicate, a difference
without destruction. Unfortunately it only holds about an ounce --
someone should make one that holds 8 ounces. I'm sure they could sell a
ton, I mean at least 50 worldwide.

> No need to butter you up. I am sure that many will join me in saying that
> you have done, and do, a hell of a lot for alternative processes.

The Terry King medal for service to the field!? Oh, oh, I can say no more,

Judy