I first discovered Nikola Tesla's Purple Plates in a Linda Goodman book. I completely forgot about what I had read until recently when I came across a couple of websites on the subject.
These links will help you get an understanding of what they do:
Do they work? In my opinion, yes!
I bought a medium purple plate on eBay for $16AU (rrp $45AU) and a couple of pendants for around $8-10 (rrp $30AU)The seller was from St Louis, USA - in this case buying from an international seller worked out a lot cheaper than buying locally from a shop.
VERDICT - SUCCESS!!
Nikola Tesla's Purple Plates