The most important of the 4Cs of diamond grading. Technically speaking, cut is not about the shape, but how well the stone interacts with light, and the quality of light emitted from the stone. This is measured as brilliance (brightness of light reflection), scintillation (flashes of sparkle when the stone moves), fire (dispersion of light shown as colours) — and finally, finish (the quality of final treatment and polishing). Proportions and symmetrical facets are key factors, along with width, depth, table and girdle> which are all considered when judging diamond cut. Where all factors are in balance, an ‘excellent’ diamond cut will have even areas of dark and light. Traditionally, all stones were shaped and polished as rounded cabochons — it wasn’t until the late 13th century and the development of technology that allowed stone cutting that the modern faceted cuts were born.