Re: gum printing pigment

From: Katharine Thayer ^lt;[email protected]>
Date: 10/09/05-03:10:11 AM Z
Message-id: <4348DE68.1BB4@pacifier.com>

maria ahlberg wrote:
>
> Hi
> I am going to use ivory Black, Daler Rowney. I will make a stock solution
> with gum arabicum and this black pigment. How much pigment in gram to 100
> ml gum.
> Is there somone in the list who can give me some ideas.

Hi Maria,
I can't give you grams paint per ml gum, since I don't measure paint but
just squeeze it in and mix til it doesn't get any darker. (Then, if for
some reason I want a less saturated color for a particular print, I add
gum to that stock mix). BTW, Loris' idea of brushing the pigment-gum
mixture on a piece of white paper to judge color saturation is a great
idea. I do this a lot, especially when mixing colors; there's always a
piece of scrap paper by the mixing table, covered with dabs of all
different colors.

The different numbers you've been given show the variability across
manufacturers that has been pointed out by several folks.

But what I'm writing about is that 100 g gum seems a lot to mix all at
once. At John's figure of 1 g to 5 ml gum for Rowney ivory black, you'd
need to use one whole tube and 1/3 of a second tube of paint for 100 ml
gum. I'd recommend mixing a smaller quantity (I mix about 25 ml gum at
a time and keep the mixtures in 35mm film canisters) and experimenting
until you're sure you've got both the pigment and the ratio that works
best for you.

Besides, gum differs as to its keeping qualities when mixed with
pigment. My favorite gum, the old Photographers' Formulary gum, kept
forever mixed with paint; I have canisters of rarely-used colors,
mixed with that gum 15 years ago, that are still as good as the day they
were mixed. But I've learned that not all gums keep as well. The gum
I've used most in the last couple of years, the Daniel Smith premium
gum, doesn't keep well at all once mixed with paint; it seems to dry up
in the canister in a fairly short time, leaving a dried up tarry residue
that can't be used, can't be cleaned out of the canister, won't mix
with fresh gum-- the canister simply has to be thrown away. Now that I
know this, I will probably be using a different gum in the future. But
at least when the stuff dries out and has to be thrown out, I'm "only"
throwing away 10-15 ml of gum per color. My point being that given the
different keeping qualities of gums, maybe you'd be better off keeping a
smaller portion of gum mixed with pigment, unless you plan to make a lot
of really huge black prints in a very short time.
Katharine
Received on Mon Oct 10 00:04:30 2005

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