Copper colloid size and failure modes Copper-based "red goldstone" aventurine glass exists on a structural continuum with transparent red copper ruby glass and opaque "sealing wax" purpurin glass, all of which are striking glasses, the reddish colors of which are created by colloidal copper. The key variable is controlling the colloid size: goldstone has macroscopic reflective crystals; purpurin glass has microscopic opaque particles; copper ruby glass has submicroscopic transparent nanoparticles. The outer layers of a goldstone batch tend to have duller colors and a lower degree of glittery aventurescence. This can be caused by poor crystallization, which simultaneously decreases the size of reflective crystals and opacifies the surrounding glass with non reflective particles. It can also be caused by partial oxidation of the copper, causing it to redissolve and form its usual transparent blue-green glass in ionic solution. When reheated for lamp-working and similar uses, the working conditions should control the temperature and oxidation as required for the original batch melt: keep the temperature below the melting point of copper (1084.62 °C) and use an oxygen-poor reducing flame, or risk decomposition into the failure modes described above. Non-copper goldstones Goldstone also exists in other color variants based on other elements. Cobalt or manganese can be substituted for copper; the resulting crystals have a more silvery appearance and are suspended in a strongly colored matrix of the corresponding ionic color, resulting in blue goldstone or purple goldstone respectively. Green goldstone, or chrome aventurine, forms its reflective particles from chromium oxides rather than the elemental metal, but is otherwise fairly similar. The non-copper goldstones are easier to work with when reheated, due to the less stringent reduction requirements and higher melting points of manganese (1246 °C) and cobalt (1495 °C). See also Helenite References Chemisches Zentralblatt: Vollständiges Repertorium für alle Zweige der reinen und angewandten Chemie, Volume 1, page 891 Harry Boyer Weiser, Inorganic Colloid Chemistry, Volume I: The Colloidal Elements, 1933 reprinted 2007, page 142 External links Murano, Its Glass and Its People. Earliest documentation of goldstone cited as 1626. Gemstones Glass types Glass art