Chipboard technique for Scrapbooking outback

If you look closely at the celtic knot chipboard from Twiddlybitz on this layout you can see it looks rusty.
Here's how you go about it.
1. First buy a container of Rusting powder( from Twiddlybitz).It looks like fine grey iron filings.(It might be!)
2. Cover the chipboard shape with Mod Podge
3.Sprinkle with rusting powder,shake off the excess.
4.Place on newspaper or blotting paper.
5. Spritz with vinegar.Allow to dry overnight.
6.Using an old toothbrush over the surface when dry it will reveal the rusted look.
This can also be done on paper flowers.