A process includes coating a cylinder having an inner wall and a cylinder axis
with a gel coating on the inner wall. Then a specimen mixture including solvent
is made to flow through the cylinder while the cylinder is being continuously rotated.
The specimen mixture is initially directed to flow along the cylinder axis and
such that specimen particles from the specimen mixture are accelerated off the
cylinder axis toward the inner wall, so as to form a film of specimen particles
embedded into the gel coating.