Step 6: Mask thine tiles!
But wait! Before you go grab that blue painters tape out of your closet, don't forget that powder coating takes place in an oven at about 400-450F. At that temperature, pretty much every tape that exists either burns or melts. Lame. Oh wait...except one: Kapton! Kapton is that gold film that was used on the outside of the lunar lander and is super heat resistant, and nearly impervious to radiation. Cool! Better yet, its decomposition products are only carbon monoxide and carbon dioxide, thus making it totally safe in lasers - no equipment damage, no gassing out the room.
The biggest downer to kapton is cost. I haven't been able to find a supplier that sells a small amount of the stuff (if you know of one, I'm all ears!), so you end up having to buy the stuff in 36 yard increments. Ouch. I ended up ordering 1" wide, 2mil thick kapton tape from Uline for this project at a cost of $54...double ouch! Granted it will last me for awhile though. Also, although I ordered the 2mil stuff (I was concerned about handling and stability), I think if I had to order it again, I'd only get 1mil...which would knock the price down to $31. The film is really tough, so 2mil is pretty overkill.
After you have the tape, simply cover the top of your tile in it, making sure to keep it away from the jigged edges, and overlap the tape a bit where you need to.