From the Philadelphia Museum of Art description:
An embossed metal basin probably inspired this design, of which only six examples are known, each with a different central image. In Florence and elsewhere, the biblical heroine Judith sometimes represented civic victory over a powerful foe; however, her depiction as a nude figure is unusual, as is the superior quality of the painting.
They make it sound like they rarely saw a nude Judith or a Judith that was skillfully painted. Obviously never read this blog.