Sanding
Procedure
Secure (glue) die to surface
Use fine sandpaper (1200+?) to remove a layer
Using polishing paste, Dremel polish layer to photographic quality
Advantages
Materials readily available
Safe (for user)
Low cost
Disadvantages
May not be as repeatable as chemical etching
Labor intensive
Risky, easy to grind too far
Notes
Nohl used Dremel + sandpaper for his MiFare Classic attacks according to CCC talk