The archetype of a bowl: a half sphere. Problem with half spheres: they tip over. That's why we usually add a rim to the bottom, of flatten the base.
This bronze bowl by John Pawson, the famous minimalist architect, is that perfect hemisphere. No flatness on the base that disrupts the smooth curve of the profile - but this bowl can still sit perfectly upright or slightly tilted.
This is all thanks to an entirely invisible but no less fundamental second material: sand, contained within the double walls of the bowl.
Pawson made his perfect bowl as part of a series of '5 Objects' for When Objects Work.