Melsdad,
Not clay or Bondo...having worked for my father as a dental technician from the time I was 6 until I left for the Naval Academy at 19, I use a lot of dental techniques and materials for gun work including castings, etc. (I keep a fairly well set up and stocked dental laboratory handy because I make my own crowns when required and end up making a lot of dental prosthetics for family members....and my Dad, who is 90, still does better work than I do....)
To hold a lot of unusual shaped pieces firmly and without damage for engraving, I often use something we called "cold cure". It is a powdered acrylic that is mixed with a monomer liquid to the consistency of peanut butter. The part is set in place on any convenient substrate, in this case a wood block, and the acrylic sets up very hard in a couple of minutes. The part can be released with heat when the engraving is done. This acrylic is the same material used to make the pink body of a denture. The material I am using here is clear / white rather than pink. Like Bondo, and as Taylor points out, the acrylic holds the part very firmly so there is no vibration or "bounce" while engraving.
Mountainman,
Yes, that is Dykem. I use many methods to get the original design down on the part, but often just Dykem the surface and sketch the design very, very lightly with a sharp scribe. The part looks like this while I am working:
Here the side plate has been attached to a scrap piece of wood with Super Glue (also later released by heat), coated with Dykem, the design sketched, and then cut. Before I remove the Dykem, I blacken the engraving with a "Q" tip and Brass Black. In the fresh cuts, the Black works immediately and the Dykem keeps the rest of the surface from blackening. Once the cuts are black, I wipe off the Dykem with lacquer thinner.
