Maltby calls theirs Diamonized Black Metal (DBM as most refer to it), it was first into,d on the MG wedge, PVD will wear quick, at least that's my experience!....literature on the site=
The Diamonized Black Metal finish is a very thin chemically implanted coating that is twice as durable as traditional nickel chrome plating and 30 times more durable PVD coatings typically found on modern black wedges. The DMB finish will not “crack” or “peel” when being bent (+/- 1 degree) to custom specs yet is so strong it will actually extend the sharpness and overall shape of the precision milled MG grooves vs. any other wedge finish currently available
