The split is 60/40, where Indiewalls takes 40% and the artist gets 60%. That means if you price your artwork at $1000 and your piece is purchased, you will take home $600.
Note, that the cost of production is added in separately from the artist fee. Therefore, if the work is being printed and/or framed by Indiewalls then the retail cost of the artwork will be higher than the price for the piece listed when you input pricing on your profile.
We find it more useful for our artists to define the price once a negotiation has been generated, taking into account what they want to make rather than the prices they want to be retail, and our formula will take care of the rest.