LRF, I use Renaissance wax with just a pinch of lamp black to blacken it and this gives the engraving good contrast and protects the metal as you say. I use that on any grayed metal and also on plated metal just for the darkening of the cuts.

Doug, you might contact Marty Rabeno about what he uses. A lot of his engravings have beautiful grayed finishes applied.

Sam Welch