Anco il vase più puro;"
and by Francis (vol. iii. p. 39.):
"And joy th' untainted vessel to begrime."
The passage is well explained in the note to Baxter's Hor. (p. 310. edit. 1809):
"Incrustari vas dicitur cum aliquo vitioso succo illinitur atque inquinatur."
And the passage in the 18th satire of Lucilius shows that this is an accurate explanation:
" . . . . . Regionibus illis
Incrustatu' calix rutâ caulive bibetur."
A practice, I rather think, prevails in some parts of England of rubbing the inside of a vessel with sweet herbs, in order to flavour cyder or other liquor.
It appears from the same note: