How such a painter sets himself to paint?

Suppose that Joseph, Mary and her Babe

A-journeying to Egypt, prove the piece:

Why, first he sedulously practiseth,

This painter,—girding loin and lighting lamp,—

On what may nourish eye, make facile hand;

Getteth him studies (styled by draughtsmen so)

From some assistant corpse of Jew or Turk

Or, haply, Molinist, he cuts and carves,—

This Luca or this Carlo or the like.