The masters used all sorts of tools and techniques to get the job done and not just lenses. They used calipers to assist converting proportions off a live model into a gigantic block of marble (to be carved into a statue), they used the pounce technique to apply a correctly proportioned underdrawing (first drawn flat) on to a curved section of ceilings (for frieze work, etc.). Added crushed glass to their palettes to raise the intensity/reflectivity of their paintings (Venetian painters). Used male models as refs for female figure work (Michelangelo).
Also…a lot of Sr. Artists opened studios to train apprentices. Best work that comes out of the shop, out of the hands of the assistants… guess who ends up signing these or ends up getting credit in the art history books. The Sr. Artist.


