the process is really simple and most thrift stores have a good selection of old brooches.
what you'll need:
-brooches, of course
-jewelry glue, i got mine here
-adjustable rings, which you can get here
-[possibly] a metal filer
what you do:
-using pliers remove the pin on the back of the brooch
-if the surface isn't even you may need to take a metal filer to the back surface
-if you have an even surface, apply glue and let it sit
voila! i've been really into the look of the wider brooches that extend past one or two fingers...something different..