You can knead in some gum-tex to make it dry rock hard. I wouldn't recommend letting anyone eat the parts with the gum-tex though (my daughter ate some and she was backed up for days 
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Oh, so sorry about your daughter! I'll keep that in mind. 
Can you tell me how much of the Gum-tex to add to a regular batch of MMF (16 oz. marshmallow)? Does it change the consistency of the MMF? How long will it need to dry before putting on the cake? Thanks for your help!
I just knead it in until I feel the MMF start to stiffen up, then I know it's enough and I quit adding more. It will dry out faster than plain MMF, so wrap it up right away. I've never done a whole batch of MMF with it...I usually will use up my leftovers by making roses, and I add the gum-tex to that because it works a lot better than plain MMF.
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