Crossword Genius

An early form of home-decorating? (4,8)

Ross

I believe the answer is:

cave painting

I'm a little stuck... Click here to teach me more about this clue!

'an early form of home-decorating?' is the definition.
I can't judge whether this definition defines the answer.

'an early form of home-decorating?' is the wordplay.
I cannot quite see how this works, but
'an' could be 'i' (Roman numeral for one) and 'i' is found within the answer.
'home' could be 'in' ('he's home' can mean 'he's in') and 'in' is present in the answer.
This explanation may well be incorrect...

Can you help me to learn more?

I've seen this clue in The Globe and Mail.
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