Re: My own PVA glue sizing experience (attn: marek + the gum woesagain)
My understanding is the "absolute humidity" is very important in gum printing (and many other alternative processes). Relative humidity (RH) percentage - as measured by ordinary hygrometers - is not much useful alone to judge the water content of air; you must also take temperature into account. See this: http://www.tis-gdv.de/tis_e/misc/klima.htm My workflow is to coat the paper, wait 5 minutes (to the point where the emulsion becomes pretty tacky / almost dry, meanwhile I clean the mixing vessel and brushes), then dry further with a hair dryer at low setting (until it's dry to the touch), and finally humidify the paper using an ultrasonic humidifier. The only part I have to be consistent is the humidifying *ritual*. (Note the emphasis!) With this workflow, my exposure times are constant and/or comparable all year round in almost every possible indoor environment condition I may encounter (given I'm using the same paper; different papers may hold different amnt. of water - also, the emulsion formulations should be similar), since there is always the same amnt. of moisture in the paper. I also keep the paper isolated during exposure by placing an impermeable plastic sheet under it; the felt in the contact printing frame's back may draw or introduce moisture during exposure. (Something I learned printing pop palladium.) Hope this helps, Loris. 2009/10/23 phritz phantom <email@example.com>: > ... > regarding humidity, > since you know a lot more about the subject than me, > do you think a change in weather (from a normal, sunny autumn day, to a > rainy day) could change the humidity within my apartment in a way that it > affects the drying of the gum emulsion? > iirc, you humidify your paper before coating and/ or printing?