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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 figure.

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.

On Oct 28, 2009, at 9:04 AM, phritz phantom wrote:

hi christina,
one question about your experiment:
how were the two vessels kept? as i understood, one was out in the open, the other one kept in the dark. covered with a lid?
in about a week, i'd expect a lot of evaporation. and if one was kept in the open, the other one in some kind of small space (a cupboard or box), the difference in the ambience (mostly because of the difference in humidity in the air, i think) could make for a noticeable difference in evaporation.


Christina Anderson schrieb:
I have, Keith. I did an experiment a while ago that I photographed. I put it on my website here:


Feel free to draw your own conclusions, or not :)