Blue Goldstone

Blue goldstone is made in glassworks, not mined. Goldstone glass is melted with metal compounds and cooled slowly in an oxygen-poor (reducing) atmosphere so that metallic crystals grow inside it; for the blue variety, cobalt is added to colour the glass. A version with copper crystals in a dark blue glass was developed in Venice (Murano) in the late 19th century. Today much of the goldstone sold as a gem and lapidary material comes from factories in China.

In blue goldstone the blue comes from the glass itself, and the crystals tend to look silvery rather than coppery. Under 20x magnification the metallic crystals are easy to see; their uniform shape, uniform size and even distribution through the glass separate goldstone from natural aventurine quartz and sunstone. Blue goldstone can resemble lapis lazuli. Gas bubbles, as in other glass, are sometimes visible.

According to a 2013 study of Venetian aventurine glass by Moretti, Gratuze and Hreglich, the variety with copper crystals in a dark blue glass is attributed to the Murano glassmaker Vincenzo Moretti around 1885. The same study notes that an older Venetian recipe already added zaffre (a cobalt oxide preparation), anticipating the blue version by more than a century. Blue goldstone shares the longer history of goldstone, which began in 17th-century Murano.