facette

Facet comes from the French facette, the diminutive of face, from the Latin faciēs (face, appearance, form). The word entered English in the seventeenth century, initially in the gemstone-cutting sense. A facet is a flat surface cut onto a gemstone at a precise angle to control how light enters and exits the stone. Each facet is a tiny face — the stone looks at you from many angles simultaneously.

Before faceting, all gemstones were cabochons — smooth, rounded domes. The first crude facets appeared in the late 1300s, when European cutters learned to polish flat surfaces onto diamonds using diamond dust. The point cut (a diamond polished into an octahedron) was the earliest form. The rose cut, with a flat bottom and triangulated top, appeared in the 1500s. Each advance in cutting technology was an advance in controlling light.

Marcel Tolkowsky, a Belgian mathematician and diamond cutter, published Diamond Design in 1919. He calculated the precise angles that maximize light return in a round diamond: 57 facets, a crown angle of 34.5 degrees, a pavilion angle of 40.75 degrees. His 'ideal cut' became the template for the modern brilliant cut. A twenty-four-year-old with a slide rule defined what diamonds would look like for the next century.

The figurative meaning — 'a facet of the problem,' 'many facets to her personality' — appeared in the seventeenth century, almost simultaneously with the gemological meaning. Both senses share the same insight: a complex thing can be understood by examining its surfaces one at a time. Each facet shows you one face of something too complicated to see whole.