"Galls are irregular plant growths which are stimulated by the
reaction between plant hormones and powerful growth regulating
chemicals produced by some insects or mites. Galls may occur on
leaves, bark, flowers, buds, acorns, or roots. Leaf and twig galls are
Quoted from this site, which has more information about oak galls:
The most common galls are created by the common gall wasp. Galls can
be found on many oak, oak-apple, and pistacio trees. If you have one
in your area, keep an eye on it, and you may be able to get the galls
off it. Ask people in your area, also; they may have an oak tree or
other tree with galls.
Gardening sites say to pick oak galls off the tree no later than
August to protect the tree. Does anyone know the best time to pick the
galls for paint? I'm going to do this, too, for oak gall ink for my
husband's calligraphy, if I can find the oak galls in my area.
Picking your own oak galls is the cheapest way to get oak gall powder,
but you'll have to crush them yourself...not sure the preparation of
the galls for crushing, but you'll need a mortar and pestle to crush
the oak galls and lots of time. You could also purchase whole galls
instead of picking them. Gall powder will be much more
money-consuming, because crushing galls is time-consuming
Hope that helps a little...sorry I can't provide more information.
Vivat the Dream,
Lady Julienne fille Gaspard, mka Jewel Shuping