Abstract: A crucible of a resistive material has a smoothly rounded inner bottom and a radially outer portion of the outer bottom having a rounded shape. The shape of the outer bottom bears a predetermined relationship to the shape of the inner bottom. In one embodiment of the invention, the outer bottom and inner bottom have a common radius of curvature, whereby the thickness of material between the outer and inner bottom is constant. In a second embodiment of the invention, the centers of curvature differ, whereby the resistivity of material at differing radii is tailored.