Fill the balloon with water . This image illustrates why you don't completely fill the balloon you should always leave some room in the neck of the balloon, then as the form dries the pressure has somewhere to go and your clay wont split like that.
Poems by Sa`di Sa'di (1213/19–92) Object Name: Album leaf, non-illustrated Date: 16th century Geography: Iran Medium: Ink, opaque watercolor and gold on paper @metmuseum