A cut above the rest

In 1673, the jeweller to the French court, Sieur Pitau, was given the task of cutting a triangular lump of blue diamond weighing over 112 carats. When he had finished, the faceted jewel weighed just 67 carats — almost half had been lost.

Over the years, the stone has been recut, shrinking it even further. Its remaining fragment — the Hope Diamond, in the Smithsonian Museum, Washington — weighs a little over 45 carats. The stuff of legends, but a nightmare for a gem merchant.

It’s inevitable that material is lost when transforming a rough precious stone into a finished gem. Cutting has always been the preserve of craftsmen, but engineers are seeking to automate the process. Machinery and computers, it seems, might be the way to minimise the amount of lost material and extract the maximum value from the stone.

At Germany’s Fraunhofer Institute, Karl-Heinz Küfer is leading a project to produce a fully-automated gem-cutting plant. He is developing software which will measure the rough stones accurately; decide what shape stone would fit best inside the rough shape; and control grinding and polishing machinery to produce the final stone.