Use 1/4" MDF, particleboard or plywood to create a positioning fixture to hold your bowl in position while you use the paper masks to check your pattern and for actual engraving. The board needs to be wider and longer than the bowls largest diameter. Mark a spot approximately centered in the "X" plane and far enough down in the "Y" plane such that the bowl can be placed there without being outside of the laser's path.

Put the marked board on the laser bed, tight up against the upper left corner of the laser bed. Disable the X-Y drive on the laser and use the red dot to position the laser over the mark you made on your positioning fixture board. Set this position as "Home".

In your drawing program create a circle slightly larger than the diameter as the foot of your bowl; about +.010 should do. Set the line width to "hairline" and the laser to "center engrave" and cut the circle out of the positioning fixture.

Check that the positioning fixture is snug to the upper left corner of the laser bed.