While I realize you folks are talking about gum, just want to mention
that humidity in the room has big effects at several points in Pt
printing as well. The humidity level of the room and of the paper
influences the exposure/printing process which is primarily chemical,
but the actual coating of the sensitizer onto the paper changes too, and
that's primarily a mechanical operation. Paper that's either bone dry or
amost soggy-damp won't coat well. People who've struggled with coating
and have begun to think they are hopelessly inadept discover it's not so
hard if they get the paper's humidity right. Naturally, just what
"right" is--you guessed it--depends on which paper. Hey, what's another
variable among friends?
>
> ---Carl