I've had these pics kicking around since I made the big girl her pencil case last year.
I thought the "how to" might be of use.
I always buy my "magic disolving stuff" from Bustle & Bows. They know what I mean when I ask for that but you might want to call it Aquasol or water soluble plastic if you're asking for it in store.
This is not only useful for embroidery but I imagine many other crafty pursuits. I saw a similar product used to create a super fluffy critter on a blanket recently.
How To - Embroidery On Dark FabricView more presentations from kootoyoo.
You can pick up the PDF How to - Embroidery on dark fabric here.