Cake decorating experts: Advice on run out icing please!

[boogiewoogie]

Can I do one straight over an iced cake or do I need to do it separately on a piece of acetate then stick it down with icing?

It's DD's birthday this Sunday and I need to start getting it ready tomorrow I think! I'm planning to do a Hello Kitty run out icing on top of buttercream cake but will that work? Will the buttercream just make it difficult to dry if I did it that way?

Would really appreciate advice please! I'm going to be now but I'll be back tomorrow pm.

TIA

Definitely do it on something first like grease proof paper/acetate first and let it dry and then transfer to the cake. You may not get clean lines straight onto a buttercream covered cake and if you mess a bit up then you'll be done for trying to get it off the buttercream without makin a bigger mess! Also the moisture from the buttercream may stop it from setting properly, it'd probably just get a hard skin but stay quite soft underneath that.

Thanks for replying frootshoots. I thought that might be the case re butter icing. Would I also need to grease the acetate first too to make it peel easier?

Yep, spread a very thin layer of trex or another shortening onto the acetate before you put any icing on that, I didn't once and my lovely teddy bear cracked in half