Here is a small gray scale image engraved into the back of a mirror as seen from the front side (note fan and ceiling reflection). I engraved it with PEP5 in VFR (variable feed rate) mode.
About 3x3 inches / 76x76 mm - 3 minutes - 75ipm (1905mm/m) feed rate - 75 ipm for white - 20ipm (508mm/m) for black - 75ipm for no burn setting - pixel resolution - 0.007 inch / 0.1778 mm
Selected 'Negative' option and flipped the image. Engraving power was S255 max. - S0 min.