Homebrew PCBs

Just got a moment to drop the CMYK mask into the exposure box with a
step gauge on it.  Results: after three HOURS of exposure, neither
black nor yellow allowed enough UV through to expose even step 0.
Cyan and magenta were tied at step 11.  So it looks like, with my inks
(Epson Claria), I can use either black or yellow, and don't need to
mix them to get "darker" patterns.

Note that the CMYK mask was printed with my program (posted
previously), not with the Gimp, as the Gimp won't put down a 100%
coverage pattern for yellow (and not quite 100% for black either).