Goldstone is a type of glitter

Glitter

Glitter describes an assortment of very small pieces of copolymer plastics, aluminum foil, titanium dioxide, iron oxides, bismuth oxychloride or other materials painted in metallic, neon and iridescent colors to reflect light in a sparkling spectrum...

ing glass

Glass

Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...

 made in a low-oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 reducing atmosphere

Reducing atmosphere

A reducing atmosphere, also known as a reduction atmosphere, is an atmospheric condition in which oxidation is prevented by removal of oxygen and other oxidising gases or vapours. Usually nitrogen is used or in more extreme conditions hydrogen gas. In that case the atmosphere is reducing...

. The finished product can take a smooth polish

Polishing

Polishing is the process of creating a smooth and shiny surface by rubbing it or using a chemical action, leaving a surface with a significant specular reflection In some materials polishing is also able to reduce diffuse reflection to...

 and be carve

Lapidary

A lapidary is an artist or artisan who forms stone, mineral, gemstones, and other suitably durable materials into decorative items such as engraved gems, including cameos, or cabochons, and faceted designs...

d into bead

Bead

A bead is a small, decorative object that is usually pierced for threading or stringing. Beads range in size from under to over in diameter. A pair of beads made from Nassarius sea snail shells, approximately 100,000 years old, are thought to be the earliest known examples of jewellery. Beadwork...

s, figurine

Figurine

A figurine is a statuette that represents a human, deity or animal. Figurines may be realistic or iconic, depending on the skill and intention of the creator. The earliest were made of stone or clay...

s, or other artifacts suitable for semiprecious stone, and in fact goldstone is often mistaken for or misrepresented as a natural material.

Nomenclature

Another common name for the material is aventurine glass, based on the original Italian

Italian language

Italian is a Romance language spoken mainly in Europe: Italy, Switzerland, San Marino, Vatican City, by minorities in Malta, Monaco, Croatia, Slovenia, France, Libya, Eritrea, and Somalia, and by immigrant communities in the Americas and Australia...

 name avventurina (from avventura, "adventure" or "chance"). It is also sometimes called "stellaria" or "sun sitara" (sitara = "star" in Sanskrit

Sanskrit

Sanskrit , is a historical Indo-Aryan language and the primary liturgical language of Hinduism, Jainism and Buddhism.Buddhism: besides Pali, see Buddhist Hybrid Sanskrit Today, it is listed as one of the 22 scheduled languages of India and is an official language of the state of Uttarakhand...

) for its starry internal reflections, or "monk's gold" or "monkstone" from folkloric associations with an unnamed monastic order.

The material is sometimes called sandstone

Sandstone

Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...

 when used in watch

Watch

A watch is a small timepiece, typically worn either on the wrist or attached on a chain and carried in a pocket, with wristwatches being the most common type of watch used today. They evolved in the 17th century from spring powered clocks, which appeared in the 15th century. The first watches were...

 dials, despite its lack of resemblance to the porous, matte texture of the natural stone.

Curiously, "aventurine" glass is one of the few synthetic

Chemical synthesis

In chemistry, chemical synthesis is purposeful execution of chemical reactions to get a product, or several products. This happens by physical and chemical manipulations usually involving one or more reactions...

 simulants to provide the eponym

Eponym

An eponym is the name of a person or thing, whether real or fictitious, after which a particular place, tribe, era, discovery, or other item is named or thought to be named...

 for the similar natural stones. The mineral

Mineral

A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...

 name "aventurine

Aventurine

Aventurine is a form of quartz, characterised by its translucency and the presence of platy mineral inclusions that give a shimmering or glistening effect termed aventurescence....

" is used for forms of feldspar

Feldspar

Feldspars are a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth's crust....

 or quartz

Quartz

Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...

 with mica

Mica

The mica group of sheet silicate minerals includes several closely related materials having highly perfect basal cleavage. All are monoclinic, with a tendency towards pseudohexagonal crystals, and are similar in chemical composition...

 inclusions that give a similar glittering appearance; the technical term for this optical phenomenon, "aventurescence

Aventurescence

In gemology, aventurescence is an optical reflectance effect seen in certain gems. The effect amounts to a metallic glitter, arising from minute, preferentially oriented mineral platelets within the material. These platelets are so numerous that they also influence the material's body colour...

", is also derived from the same source.

Production

The original manufacturing process for goldstone was invented in seventeenth-century Venice

Venice

Venice is a city in northern Italy which is renowned for the beauty of its setting, its architecture and its artworks. It is the capital of the Veneto region...

 by the Miotti family, which was granted an exclusive license by the Doge

Doge of Venice

The Doge of Venice , often mistranslated Duke was the chief magistrate and leader of the Most Serene Republic of Venice for over a thousand years. Doges of Venice were elected for life by the city-state's aristocracy. Commonly the person selected as Doge was the shrewdest elder in the city...

. Persistent folklore

Folklore

Folklore consists of legends, music, oral history, proverbs, jokes, popular beliefs, fairy tales and customs that are the traditions of a culture, subculture, or group. It is also the set of practices through which those expressive genres are shared. The study of folklore is sometimes called...

 describes goldstone as an accidental discovery by an unnamed Italian monastic order or medieval alchemists, but there is no pre-Miotti documentation to confirm this.

The most common form of goldstone is reddish-brown, containing tiny crystals of metallic copper that require special conditions to form properly. The initial batch is melted together from silica, copper oxide, and other metal oxides to chemically reduce the copper ions to elemental copper. The vat is then sealed off from the air and maintained within a narrow temperature range, keeping the glass hot enough to remain liquid while allowing metallic crystals to precipitate from solution without melting or oxidizing.

After a suitable crystallization period, the entire batch is cooled to a single solid mass, which is then broken out of the vat for selection and shaping. The final appearance of each batch is highly variable and heterogenous. The best material is near the center or "heart" of the mass, ideally with large, bright metal crystals suspended in a semitransparent glass matrix.

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

Purpurin (glass)

Purpurin , sometimes referred to as glass porphyr, is an opaque glass of brownish to lustrous deep-reddish color which in classical antiquity was used for residential luxury objects, mosaics and various decorative purposes...

, all of which are striking glasses whose reddish colors 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

Glass

Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...

 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

Cobalt

Cobalt is a chemical element with symbol Co and atomic number 27. It is found naturally only in chemically combined form. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal....

 or manganese

Manganese

Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...

 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

Chromium

Chromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...

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).

External links

• http://www.dvpaperweights.org/newsletters/murano_pt1.html Earliest documentation cited as 1626.