Looking for a craft/art product

Quite some time ago, I saw a segment on HGTV which intrigued me. Did I write doen the segment number.... Duh!

An artist was the guest, and she first painted canvas with (as I recall) a 'black iron oxide' paint. When dried for 24 hours, she spritzed it with a simple water spray.... and as the 'iron' particles in the paint reacted with the water, they 'rusted' some amazing colors reminiscent of the Southwest.

I'd like to do this technique, although not on canvas. Google searches just turn up 5 gallon buckets of iron oxide. Any suggestions?

TIA, darius