I use Brilliance marking spray to give the charm a nice dark image.

I apply 2 light coats to the metal piece and allow to dry fully between coats

I keep the round outline of the design set to ignore. Before I start to frame the piece I set that circle to output and change the framing option to outline instead of rectangle. Then click framing to give you an accurate placement of your charm. 

Stop framing. 

Make sure to go back and set the circle outline back to ignore so this shape won't engrave on your piece.

Engrave your piece and clean the charm with soap and hot water. I use a dab of Dawn dish soap on the charm and rub between my fingers or use an ultra soft tooth brush gently and then wash it off under a steam of hot water. this removes all of the brilliance spray residue. 

I use a lint free micro fibre cloth to dry.

Attach your split ring and jump ring to the charm and your key chain is finished!