Old Art to assess and embellish (8)

I believe the answer is:

decorate

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'embellish' is the definition.
(I know that embellish can be written as decorate)

'old art to assess' is the wordplay.
'old art' becomes 'deco' (I can't explain this - if you can you should believe this answer much more).
'to assess' becomes 'rate' (rating is a kind of assessing).
'deco'+'rate'='DECORATE'

'and' is the link.

Can you help me to learn more?

(Other definitions for decorate that I've seen before include "Make more attractive" , "'Adorn, beautify (8)'" , "paint" , "Honour" , "Beautify by additions" .)

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

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