Today diamonds are prized for their brilliance and fire, but for centuries they were best known for their adamantine lustre, or ability to refract light. As the practices of gem cutting evolved, diamond polishers learned how to take the dark lustre the diamond was known for and turn it into the fiery gem we know today.
Unlike today's diamonds, from the popular emerald and brilliant cut to the new crisscut, diamonds in the Middle Ages and Renaissance were cut to look dark. The flat black diamonds in old paintings are usually table cut diamonds. Many people in the Renaissance preferred rubies, emeralds and other colored gems to diamonds. The colored gems were flashier, more in keeping with the fashion of the times.
Diamond polishers in Renaissance Europe spent hundreds of years developing new cuts to compete with the popular colored gems. A Flemish diamond polisher in the 1400s created a tool called the scaif, that allowed diamonds to be cut with perfect symmetry. The rose cut became the most popular style in the 1500s. This cut had a circle of triangles around the edges of the gem, like a simpler version of todays brilliant cuts, but the gem was cut flat, and didn't have the pointed bottom, or pavilion, we expect today.
The real breakthrough in diamond cuts was the creation of the first brilliant cut, or mazarin, in the 1600s. While dull compared to modern brilliant cuts, the mazarin revealed for the first time the fire hidden inside the diamonds adamantine lustre. Since then, diamond cutters have continued to experiment with variations on the brilliant cut, and new cut styles. The creation of modern cutting tools in the 1900s and the introduction of computer modeling programs have helped speed this process, bringing us the beautiful, firey gems we know and love today.