  We consider a thin elastic sheet adhering to a stiff substrate by means of
the surface tension of a thin liquid layer. Debonding is initiated by imposing
a vertical displacement at the centre of the sheet and leads to the formation
of a delaminated region, or `blister'. This experiment reveals that the
perimeter of the blister takes one of three different forms depending on the
vertical displacement imposed. As this displacement is increased, we observe
first circular, then undulating and finally triangular blisters. We obtain
theoretical predictions for the observed features of each of these three
families of blisters. The theory is built upon the F\"{o}ppl-von K\'{a}rm\'{a}n
equations for thin elastic plates and accounts for the surface energy of the
liquid. We find good quantitative agreement between our theoretical predictions
and experimental results, demonstrating that all three families are governed by
different balances between elastic and capillary forces. Our results may bear
on micrometric tapered devices and other systems where elastic and adhesive
forces are in competition.
