How is cold porcelain used in the world of cake decorating?
Not a lot. It's treated like plastic decoration in some competitions and completely disallowed in others.
Some decorators will use it if a client wants to save a deco.
If used, cold procelain must have a barrier between it and the cake as some of the ingredients aren't food safe--and it will go blotchy if it makes contact with grease (buttercream).
The techniques used in making cold porcelain items are basically the same as those used for gum paste pieces, so most decorators who prefer "all edible" default to gum paste.
its used in the same way as gumpaste - popular for flowers or figures (maybe more used in the uk than in america?). but as blakes cakes said, cant be used if its actually going to touch the cake.
Thanks for the information!