Kosar's Top 10 Gum Facts Redux-Dark Hardening

A while back Ms. Christina Z. Anderson wrote in Kosar's Top 10:

"Completely dehydrated or fully swollen coatings do not show any light
sensitivity at all, but in between the sensitivity is high when the humidity
is high. Sensitivity doubles with increase of 30% humidity."

I have found this to be true in practice. Dark hardening/humidity jumped up
and bit me on the a... I am not sure about doubling with a 30% increase,
however, since just this week I bought a hygrometer.

Question 1: Are the terms dark hardening and dark reaction interchangeable?
If I understand it correctly the term dark hardening is meant to describe
when the exposed emulsion will not develop, rub or come off even with a
brillo pad. And that this can be caused by among other things humidity.

Question 2: Will dark hardening occur even in spite of the exposure
corrections when the humidity reaches a certain point? Katherine Thayer
wrote around the same time: "Well, the dark reaction is extremely variable.
Referring back to the dark reaction test I posted the other day." Obviously
that post is long gone. What was the conclusion?

Question 3: Has anyone come up with an optimum humidity level? From reading
past posts it can actually be too low.

I had been humming along all winter having solved my sizing problems thanks
to all the great input from "the group". Now that the humidity is reaching
its spring/summer levels, I have run into a dark hardening wall. I am not
really able effect the humidity level other than to measure it (on Friday RH
ran from 65-70% while I was printing). The only alternative is to lower my
exposure time and I really would rather not waste a lot of sized paper only
to find that changing the exposure is not an option; that the darks will
still harden. I understand that subject has been covered, but am totally
addicted to gum printing, so stopping is not an option, any suggestions
would be helpful.

Thank you,

Candace Spearman
Humidity Rising in Memphis
Received on Sun Apr 10 16:37:25 2005