Chop the semisweet chocolate into small pieces.
Melt the chocolate in the microwave for 30 seconds at a time, stirring for 30 seconds in between each heating until just melted and smooth. Alternately, melt the chocolate in a pan over a larger pan of simmering water. The chocolate should not be too hot or it will melt the balloons.
Chop the white chocolate into small pieces and melt as you did the semisweet.
Put the melted semisweet chocolate in a bowl slightly larger than the balloons and dip the untied end of the balloon in, coating the lower third of the balloon with chocolate.
Flip the balloon over onto a ramekin or small glass to cool, keeping the chocolate on the top of the balloon.
Spoon some melted white chocolate into a plastic zipper bag and cut off a tiny corner of the bag. Pipe the white chocolate in a design over the semisweet on the balloon.