Abstract: An introductory outline expounds the visual effects produced when gems are cut with spherical facets, rather than with the conventionally flat ones. An indication follows of some kinematic principles and devices which enable the manufacture of this type of facet. In particular, sphere-shaped abrasive covers or bowls are foreseen on which will be fixed the gem-carrying terminal of a conventional tripodal faceter whose two other terminals of support are guided in such a way as to make gem-carrying terminal (C) describe a sphere, maintaining a constant angle between the axis of the gem and the normal to the abrasive cover at the point of contact.

Abstract: An introductory outline expounds the visual effects produced when gems are cut with spherical facets, rather than with the conventionally flat ones. An indication follows of some kinematic principles and devices which enable the manufacture of this type of facet. In particular, sphere-shaped abrasive covers or bowls are foreseen on which will be fixed the gem-carrying terminal of a conventional tripodal faceter whose two other terminals of support are guided in such a way as to make gem carrying terminal (C) describe a sphere, maintaining a constant angle between the axis of the gem and the normal to the abrasive cover at the point of contact.