Quote Originally Posted by Max Power
I came up with one full stop difference in the
readings between the grey card and the black card, and with both
my TTL and hand-held meters.

Shouldn't the TTL and hand-held meters have been 'fooled' into
reading the black card at the same value a grey card?
That is an intensity reading. Then there is the meter's recommended
exposure which is correct for the gray but not the black. If anything
the meter is never fooled. The reading it gives is always for that
gray. You'll need to stop down two or three stops for that
black reading to produce a black density.

Worry about that one stop difference. Perhaps the black material
reflects considerable blue while your gray card absorbs considerable;
or the other way around. I'd think two or three stops, maybe four,
minimum twixt black and 18% gray. Dan