I have finally had a chance to play with this technique. It is originally from Donna Kato's book - The art of polymer clay - creative surface techniques which is a book I have and love looking at. Adrienne challenged us to try this technique and has an excellent step by step blog post about it.
I am not entirely convinced by my first try mainly because I did not get a deep enough impression with the stamp and so the pattern isn't very clear in places. I still cut out lots of pieces though and here they are once baked
I made some moulded pieces too using a mould brushed with mica powders. I also just stamped into the left over clay and brushed with mica powders.
It is difficult to see the individual pieces in this photo so here are some closer ones.