I am trying to make a cake with fondant cut outs. that need to be firm enough to stand up off the cake. Do i make them days before and let them air dry, or is there a product that needs to be added to make them hard?

ok first this wiseacher answer:

give them cake viagra!

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actually -- mix them with gumpaste or tylose

http://www.confectioneryhouse.com/product.php?productid=8488
http://www.fondantsource.com/tylosec.html
http://www.nicholaslodge.com/gumpaste.htm

then yes, as you correctly figured out, let them dry for several days in a DRY environment (ie. low humidity).. (which can be hard to come by depending upon where you live -- right now it's 90% humidity outside and my dehumidifier -- in addition to the A/C -- is running full tilt to get it down to 50% inside!)

A fan can help (like in my house right on the dining room table under the ceiling fan)

oven bad idea -- could melt or worse as some have done, forget they're in there and the start to heat oven to cook and well....melted sugar in ovens is not a pretty sight or smell.

ok, thank you very much, i will have to try that. I am making it for 4-H hopefully i will get a blue ribbon.
thanks again