quote:
this method seems to be so much easier than I thought.


You're not alone. When people see paint-filled items, visions of surgical application come to mind.

That's why I posted the most common (flood) method, which, as you witnessed, is anything but exacting. :-) 

David "The Stunt Engraver" Lavaneri
DGL Engraving
Port Hueneme, CA