I havent made a ring with femo or sculpy but I can tell you how because I have extensive experience with it and other jewelery making. you'd do best to find a ring sizing cone. it's a tapered metal rod with grooves in it for each whole and half ring size and you use it to size out wire wrapped rings as well as regular rings. you would then mould the sculpy around the desired size and then bake the whole thing with the cone standing on the fat end. be careful to smooth out the sculpy well so that there will be no cracks or creases before hand and also be bery careful with baking time and temperature so that you don't over do it hope that helps
Fimo shrinks a lot though, doesn't it? That'd make the sizing a bit difficult.. wouldn't it break if you put a thin layer around a solid, unshrinkable object like a ring sizer while in the oven?
perhaps... some of the newer polymer clays dont really shrink. maybe try making it a size or two large and then baking it without the rod if a problem with breaking occurs.
