Many products are available to help you etch glass, but it's harder to find information about etching plastics such as plexiglass. Many of the etching techniques for this material are similar to the ones you'd use on glass. Sand blasting is the most effective, but requires equipment most of us don't have. A simpler method for most crafters uses a rotary tool and engraving bit.
Things You'll Need
Sheet of plexiglass at least 1/8 inch thick
Place a full size drawing or template of your finished engraving on a clean table. Lay the plexiglass over it, with the side to be engraved facing up.
Carve away the surface of the plexiglass with your rotary tool and an engraving bit. Follow the lines of your design carefully. Choose larger bits for engraving big areas, and smaller bits for fine line work. Experiment with the depth and pressure required for a good engraving.
Remove the plexiglass and brush away all debris. Compare the etched design to the template. Make changes if necessary.
Smooth down rough edges using the rotary tool.
Plexiglass is less brittle than glass, but is easier to scratch. Practice engraving on a spare piece of plexiglass. Use new bits for the best results Hydrofluoric acid (glass etching fluid) can also be used to etch plexiglass.
Follow safety precautions when etching–use goggles and a particle respirator.