on buttercream? Do I just wait until it crusts a little or let it crust really well? I need to put siding on the sides of a building and don't want to cover the whole thing with fondant. Thanks for any help!
just until it wont stick! LOL
how is that for help?
it depends upon how crusty your icing is. For em I get a good impression in 20-30 minutes with no sticking
HTH
Are they fairly easy to get a good impression with? Do you have any tips for me since I've never done this before? I'm a little nervous... 
Is it pretty easy to go back over the design if one of the lines doesn't come out well? 
Thanks again!!! 
yes, they are pretty easy to use. use a nice firm pressure and run your fingers along the whole mat to make sure all of the area gets impressed. wipe off the grease before each time you press it.
lining it up to impress again over the lines is not too easy, but possible.
use a dummy to put some bc on and practice on the side first!
HTH
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