In addition to moist paper towels, application tape can also be used to prevent the surface from roughening. With application tape, however, the engraving color is rather grayish and not bright white.
As with the paper towel method, make sure that no air bubbles and overlaps are formed when you apply the tape. After engraving, clean the glass to remove any adhesive residue.
-Josh Stephens, Trotec Laser