Models artform on great artist (3,6)

I believe the answer is:

old master

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'great artist' is the definition.
(I've seen this before)

I don't understand the rest of the clue.

(Other definitions for old master that I've seen before include "soon to leave school?" , "He was a great exponent of art" , "Could get a picture" , "Great painter of former times - or one of his works" , "Costa?" .)

I've seen this clue in the Sydney Morning Herald.

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