Goldstone

Goldstone, also known as aventurine glass, is a type of glittering man-made glass produced in a low-oxygen reducing atmosphere. The finished product can take on a smooth polish, making it ideal for carving into beads, figurines, and other artifacts often used in jewelry. While it is a synthetic material, goldstone is commonly mistaken for a natural gemstone due to its sparkling appearance.

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Goldstone is primarily composed of glass infused with reflective particles of copper. Copper-based red goldstone sits on a structural continuum with other glasses, such as transparent red copper ruby glass and opaque sealing wax purpurin glass. All these materials are visually striking, with their vivid reddish colors attributed to the presence of colloidal copper.

The glittering effect, known as aventurescence, is achieved by controlling the colloid size within the glass. In goldstone, the copper particles are macroscopic, resulting in large, reflective crystals that create its signature shimmer. By contrast, purpurin glass contains microscopic particles that give it an opaque appearance, while copper ruby glass contains submicroscopic nanoparticles that result in a transparent finish.

The outer layers of a goldstone batch often exhibit duller colors and less pronounced aventurescence compared to the inner portions. This may be due to insufficient crystallization, which decreases the size of reflective crystals while causing the surrounding glass to become cloudy with non-reflective particles.

Additionally, partial oxidation of the copper can result in the dissolution of the crystals, producing the typical blue-green glass color associated with copper in ionic form.

When goldstone is reheated for lampworking or similar purposes, careful control of temperature and oxidation is required. The conditions must be similar to those used during the initial melt, keeping the temperature below the melting point of copper while using an oxygen-poor reducing flame. If these conditions are not met, the material may degrade, losing its characteristic glittery appearance.

Goldstone – Red aventurine glass

Production

Goldstone production can be traced back to 17th-century Venice, where it was first created by the Miotti family, who received an exclusive license from the Doge of Venice. Though urban legend suggests that goldstone was accidentally discovered by Italian monks or alchemists, there is no documented evidence to support these claims prior to the Miotti family’s involvement.

Interestingly, goldstone-like materials have been found in earlier artifacts. A goldstone amulet dating back to the 12th or 13th century was discovered in Persia and is currently held in the collection of the University of Pennsylvania. This suggests that similar techniques were known to artisans long before the Miotti family’s invention.

The most common form of goldstone is a reddish-brown variety containing tiny crystals of metallic copper. To create goldstone, a mixture of silica, copper oxide, and other metal oxides is melted together. The copper ions are chemically reduced to elemental copper, and the vat is sealed off from the air.

The temperature is carefully controlled to keep the glass liquid while allowing metallic copper crystals to precipitate out of solution without melting or oxidizing.

After a suitable period of crystallization, the entire batch is cooled to form a solid mass. The glass is then broken out of the vat and selected for shaping. The appearance of each batch of goldstone is highly variable. The best pieces typically come from the center of the mass, where large, bright copper crystals are suspended within a semi-transparent glass matrix.

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