Artist>Consignment>Artwork>Payment

that is the purist way of doing it, but you may want to add an Artist_ID to
the Payment table so that you don't need to join via several levels just to
get payments for the Artist.

But I would change one thing, change payment for transaction

have at least three fields e.g. charge, payment and Artwork_ID (Artwork
table)

something like

Payment_ID numeric autonumber
Artist_ID numeric (linked to artist table)
Artwork_ID numeric (linked to the Artwork table)
Date datetime
Charge money (they have given you artwork, and you owe them this amount of
money)
Payment money (you have paid them some money)
Notes (general notes about the transaction)

you can then do a very simple select statement to view the balance by artist

select sum(Charge) as we_owe, sum(Payment) as we_have_paid from Payment
where Artist_ID=" your artist's id would give you the balance of the account

in doing the above it will give you a lot of flexability.

Hope it helps.