Mystery-set diamonds is a trademarked technique developed by Van Cleef & Arpels in 1933 by setting diamonds or precious stones in a flowing line with no metal visible. The stones are specially cut with a groove near the culet so that they can be slid onto rails and placed alongside the neighbouring stones. The rails are invisible and form a lattice underneath the solid surface of stones. This work is intricate and requires highly skilled goldsmiths and gem-cutters to work in conjunction.The beauty of this technique is the way the gems seem to float without any prongs or visible metal holding them in place. In reality, each stone is very precisely placed.