Petra Class Ring. 22k and 18k Gold, Aquamarine (11.62 cts), Diamonds (0.35ct). A recent movement in studio jewelry is the use of raw gems and Petra Class was among the early innovators. The textures of the raw material reveal its natural beauty in unexpected ways. By combining it with faceted gems, she creates a subtle contrast of texture that enhances the unique beauty of each stone and lends her work an unusual richness.