by magicdiscoman » Jan 5th, '11, 13:25
in short no, you can't overuse a shell provided you treat it as any other coin.
that said just leaving it on display for the sake of it is a golden invitation for a spec to pick it up and have a look, were possible in your routine its better to lay out say four coins in a row then imediately put them in a stack, produce a coin and tip over the stack to show only three coins.
same for coins across display overlapped in the hand then close your hand to stack the coins make one coin fly then open hand to show one coin gone.
by closing then opening your hand straight away you achieve a vanish in a blink of an eye and provide lots of misdirection to produce the traveled coin.
if memory serves sankey does a routine were he literaly picks the shell off of a coin to do a multiply and yet the audience dosn't see the action all they see is the extra coin appear, can't remember the name off hand.