Re: My own PVA glue sizing experience became: dark reaction in gumemulsion
The experiment was with UNpigmented gum. I did not pigment the
solution until time of use.
On Oct 28, 2009, at 9:50 AM, phritz phantom wrote:
didn't the emulsions seperate? not even after a week? or did you
keep agitating in some way?
any time i keep a mixed gum emulsion, the pigment sinks to the
bottom after a day or so. it looks like if it's the pigment/gum
sludge at the bottom and the dichromate on top.
Christina Anderson schrieb:
Neither were covered. Humidity was high (this was in MN in the
summer). The one was in a dark large cupboard, the other left
out. The amount in both cups didn't change that I remember and I
would have noticed, because I measured the same amount in each--
remember, it is not water, it is gum arabic. I was still,
surprisingly to me, able to pour both and use both for coating--in
other words, I expected a hardened lump but neither did so. I was
most interested in the difference between the two.
BTW I coated the paper using both solutions mixed with pigment as
well, and left both out in the sun to really bake it on, and the
continuing action wasn't as dark as the dark reaction ones...go
Phritz, this is not a controlled scientific experiment, just a
desire to see the effects of dark reaction and continuing action
that the literature discusses so much. With no pigment in the mix
it is easy to observe that both occur, but how that affects gum
printing in general (e.g. if someone were to mix a coating solution
and save it for a day or two or three--this does NOT refer to
coated paper that is saved a day or two or three which is an
entirely different story and in MT I can keep coated paper 3 or 4
days, in MN not long at all due to ambient humidity there vs.
here)--in other words PRACTICE, not testing--is the usual YRMV. You
can theorize til the cows come home, but that doesn't do much good.
I don't need a reason for a speed increase in my emulsion and
therefore just have never felt a need to let a solution age. But my
guess is, from the literature, that using aged emulsion is not as
big a deal as some of the more contemporary books say it is, so
Keith's question is a valid point as is Loris' saying to be
consistent in your testing, to take these reactions into account.