It is twice raised by an outstanding painter (6)
I believe the answer is:
titian
'painter' is the definition.
(I know that Titian is a old master)
'it is twice raised by an outstanding' is the wordplay.
'is twice' becomes 'it' (this might be a standard abbreviation I've not previously seen).
'raised by' is a reversal indicator.
'outstanding' means one lot of letters goes inside another (some letters standing outside or around others).
'it' backwards is 'ti'.
'ti'+'an'='tian'
'it' placed inside 'tian' is 'TITIAN'.
Can you help me to learn more?
(Other definitions for titian that I've seen before include "Italian painter; hair colour" , "The painter Tiziano Vecellio" , "Venetian painter - shade of red" , "Painter; red tint" , "Italian Old Master and colour" .)