I don't know if you live by a michaels but they sell kits. I've never tried them but I am going to after I perfect my shoe making
I bought the latex mold builder from Michael's and tried it. But it doesn't work for a wine glass, as you can't pull the stem over the bottom when you take off the mold (it won't stretch that far without ripping).
I have heard of playdough molds, but not sure how to do it!~
what about doing a 2 part one for the glass and the other for the stem?
Not sure how that could work with latex... I'd still have the same issue pulling the stem over the bottom of the wine glass. Then not sure how I'd make both parts stick together. Maybe I'm not picturing it right? I'm thinking I'll try a clay mold...