The piriform or pear shaped curve was first described by a French mathematician in 1886. see http://mathworld.wolfram.com/PiriformCurve.html It can be made three dimensional with openSCAD's rotate_extrude command and divided in half to make a bowl and lid. A feature of the rotate_extrude command is the ability to set the number of sides constructed and this was used to make 3 bowls which appear different but which are produced with essentially the same code. See for example teapot_lid.scad where the rotate_exrude command was used to make a second set of lids for the pear shaped bowls.
All parts need support. The bowls were inverted for printing; the support material that occurs inside is easily removed.