In subdued light -
Photo resist is available from companies that sell printed circuit board supplies.
It comes with polyfilm on both sides that must be removed so that the resist can
adhere to the brass. There's a trick to getting it to adhere without bubbles. After
thoroughly cleaning the brass and degreasing it with denatured alcohol, slip the
brass into a bath of warm water with a few drops of dishwashing soap. Remove the
brass from the water and leave it wet. Peel the polyfilm off of one side of the
resist and use a squeegee or rubber roller (my preference) to roll out all of the
bubbles. I also trim the excess resist with a single edge razor blade at this point
and re-roll the resist. Now do the second side the same way. Blot both sides, then
use a hair dryer to heat the resist and get it started drying. Set it aside in a
dark place for at least several hours before exposure.