[alt-photo] evaporation of gum mixture

[Paul Viapiano]

Hello all...

Having traced my pt/pd to a highly alkaline batch of Fabriano , I have 
another question on an entirely different subject.

Sometimes I make these little premixtures of watercolor pigment and gum 
arabic, nice and handy for printing tricolors in the same pigments. I mix 
about 1 gram pigment to 9 ml of gum.

In May, I made a mixture and weighed it at 17.9 grams in its plastic 
snap-cap container. Two months later, it weighs in at 17.2 grams. What is it 
that is evaporating? Gum arabic? I'm curious...