I have a page in color from the Burt Co. that explains what Crest & Seal
is. When I find it, I'll give to someone to scan. The "crest" is the paper
inlay with a lithographed photo, which is inbedded into the soften clay.
The "Seal" is the lacquering process that seals the entire chip & leaves a
smooth flat finish. You can't feel the inlay when you run your fingernail
across it. Without the "seal", you can feel the edge of the paper inlay.
Most "reverse" paper inlay monograms or designs that are not lithographed,
are not sealed. Think of the seal as a polyurethane coating.