To turn a rough diamond into a sparkling stone, machining is required. The main steps of machining are: cleaving, sawing, cutting and polishing. To keep the stone in place during cutting and polishing, an adjuster placed it in a lead cap (holder). It is the former way for securing the diamond. Nowadays, the sharpening tongs are equipped with clamping mechanisms.

In 1907, the Amsterdam firm Asscher was commissioned to cut the rough Cullinan. For this purpose this lead cap was used. In 8 months the stone was cleaved and ground into 9 large and 96 smaller stones. The largest, the flawless Cullinan I of 530.2 carats was mounted as the pear-shaped showpiece in the English king’s scepter.