Son starts drinking and painting in dotty fashion (9)
I believe the answer is:
stippling
'painting in dotty fashion' is the definition.
'stippling' can be an answer for 'painting' (thesaurus). I am not sure about the 'in dotty fashion' bit.
'son starts drinking' is the wordplay.
'son starts' becomes 's' (I can't explain this - if you can you should believe this answer much more).
'drinking' becomes 'tippling' (tippling is a kind of drinking).
's'+'tippling'='STIPPLING'
'and' acts as a link.
Can you help me to learn more?
(Another definition for stippling that I've seen is " Marking with small dots".)