Moody technique for painting abstract (13)
I believe the answer is:
temperamental
'moody' is the definition.
(synonyms)
'painting abstract' is the wordplay.
'painting' becomes 'tempera' (I've seen this before).
'abstract' becomes 'mental' (I can't explain this - if you can you should believe this answer much more).
'tempera'+'mental'='TEMPERAMENTAL'
'technique for' is the link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for temperamental that I've seen before include "Likely to act unpredictably" , "Subject to sharply varying moods" , "Moody, sensitive" , "Liable to mood swings" , "Having a volatile disposition" .)