The Sharpie sounds like a good quick-and-dirty method if you want it dark; not sure how long it would hold up. Patinas for stained glass (nasty stuff) and gun bluing solution would be a bit more durable. If you're just looking to take the shine off, how about vinegar or Palmolive dishwashing soap (apparently the sulphur in it does a great job of dulling brass).Regards,Scott