Crossword clue: to ornament, as shells, ivory, etc., by engraving, and (usually) rubbing pigments into the incised lines.
1 answer found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).
Possible answers
a carving (or engraving) on whalebone, whale ivory, walrus tusk, etc., usually by American whalers