I saw this on TV and was really excited about trying it out. I bought cheap shaving foam from Morrisons (26p) then....
1. Fill the tray with foam
2. Spray Mica Spray very close to the foam to get intense spots of colour
3. Swirl into random pattern
4. Place paper on top and make sure you press into the foam so the paper makes full contact with the Mica.
5. Lift paper off and use a ruler or similar to scrape the foam off the paper.
6. Lay the paper, face up, on to a piece of kitchen roll and wipe printed surface with a separate piece of kitchen roll to dry, then another piece to buff.
I used two types of card, coated card stock, which gave me a subtle colouring with no Mica glitter to it and a quality printing card that gave me an intense colour with Mica glitter. Both ways looked good and it was lots of fun.
I did reuse the same foam a few times and it just gave me different looks, definitely worth playing around with to make backing papers.