fine
sapphire on which is engraved the emperor Per-tinax. It is said there
is in the Petersburg Museum a sapphire whose colour varies from whitish
to clear blue, and on it is engraved a draped head ; so that the face
is white and the folds blue, which produces a beautiful effect. I have
a sapphire on which is the head of Vespasian in relievo ; it was found
in the Appian Way. It was copied on a blue quartz by the gifted Odelli,
a skilful Roman engraver, whose work, in my judgment, succeeded
excellently ; but the artist assured me that the quartz cuts very badly
on account of the want of closeness in the material. The same artist
engraved for me two large blue corundums, and on them he succeeded in
giving his work a beautiful finish, because, being harder, they offered
more resistÂance to the tool.
