Garry:

Do the engraving with a mask--something that adheres fairly well--then spray clear acrylic, lacquer or varnish into the engraved area. Let it dry and use whatever kind of color fill you want. Two coats are better than one.

Krylon Crystal Clear acrylic is available in many stores.

Hi Garry :

Use the same process as Mike described - spray two coats lacquer and let it dry ( two to three minutes)
I use Winton Oil Colour nr. 41 ( Vandyke Brown ).
Rub that in with a paper towel and clean the rest .
I would then spray another coat of lacquer to seal .

Good luck !

Constant Laubscher