Printed circuits caps

has anyone thought of using printed circuit board for making pulse caps? I
recently came across some surplus double sided G10 board. My data books give
the dielectric constant as 4.5, and the electrical strength as 15kV/mil.
I/ve made a small one (0.0005mfd). I ran it at 15kV for an hour, no
noticeable heating and no break down. The copper was removed for about 1/2"
all round the edge. I ran a bead of hot glue over the edge of the copper.
Capacity works out at 16pF per sq in. That means that a piece with plates
6.25x10" will give 1nF!!