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 justify this - if you can you should give a lot more credence to this answer).
'tempera'+'mental'='TEMPERAMENTAL'
'technique for' acts as a link.
I am not very happy about this link. 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" .)