Aventurine glass
   HOME

TheInfoList



OR:

Goldstone is a type of
glitter Glitter is an assortment of small, reflective particles that come in a variety of shapes, sizes, and colors. Glitter particles reflect light at different angles, causing the surface to sparkle or shimmer. Glitter is similar to confetti, sparkle ...
ing
glass Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling (quenching) of ...
made in a low-
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
reducing atmosphere A reducing atmosphere is an Atmosphere, atmospheric condition in which oxidation is prevented by removal of oxygen and other oxidizing gases or vapours, and which may contain actively Reducing agent, reducing gases such as hydrogen, carbon monoxi ...
. The finished product can take a smooth
polish Polish may refer to: * Anything from or related to Poland, a country in Europe * Polish language * Poles Poles,, ; singular masculine: ''Polak'', singular feminine: ''Polka'' or Polish people, are a West Slavic nation and ethnic group, w ...
and be carved into
bead A bead is a small, decorative object that is formed in a variety of shapes and sizes of a material such as stone, bone, shell, glass, plastic, wood, or pearl and with a small hole for threading or stringing. Beads range in size from under ...
s,
figurine A figurine (a diminutive form of the word ''figure'') or statuette is a small, three-dimensional sculpture that represents a human, deity or animal, or, in practice, a pair or small group of them. Figurines have been made in many media, with cl ...
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(s) may refer to: * Anything of, from, or related to the people of Italy over the centuries ** Italians, an ethnic group or simply a citizen of the Italian Republic or Italian Kingdom ** Italian language, a Romance language *** Regional Ita ...
name ''avventurina'' (from ''avventura'', "adventure" or "chance"). It is called "del-roba" (Persian: دلربا) in
Persian Persian may refer to: * People and things from Iran, historically called ''Persia'' in the English language ** Persians, the majority ethnic group in Iran, not to be conflated with the Iranic peoples ** Persian language, an Iranian language of the ...
which means "Charming"; or "monk's gold" or "monkstone" from
folkloric Folklore is shared by a particular group of people; it encompasses the traditions common to that culture, subculture or group. This includes oral traditions such as tales, legends, proverbs and jokes. They include material culture, ranging fro ...
associations with an unnamed
monastic Monasticism (from Ancient Greek , , from , , 'alone'), also referred to as monachism, or monkhood, is a religion, religious way of life in which one renounces world (theology), worldly pursuits to devote oneself fully to spiritual work. Monastic ...
order. Goldstone also has a green brother ( green Goldstone ) and a blue brother ( blue Goldstone ). The material is sometimes incorrectly called
sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...
when used in
watch A watch is a portable timepiece intended to be carried or worn by a person. It is designed to keep a consistent movement despite the motions caused by the person's activities. A wristwatch is designed to be worn around the wrist, attached by ...
dials, and other jewelry, despite its lack of resemblance to the porous, matte texture of the natural stone. Additionally, "aventurine" glass is one of the few synthetic simulants to provide the
eponym An eponym is a person, a place, or a thing after whom or which someone or something is, or is believed to be, named. The adjectives which are derived from the word eponym include ''eponymous'' and ''eponymic''. Usage of the word The term ''epon ...
for the similar natural stones. The
mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. ( ...
name "
aventurine Aventurine is a form of quartz, characterised by its translucency and the presence of platy mineral inclusions that give it a shimmering or glistening effect termed ''aventurescence''. Background The most common color of aventurine is green, but ...
" is used for forms of
feldspar Feldspars are a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagioclase'' (sodium-calcium) feldsp ...
or
quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical form ...
with
mica Micas ( ) are a group of silicate minerals whose outstanding physical characteristic is that individual mica crystals can easily be split into extremely thin elastic plates. This characteristic is described as perfect basal cleavage. Mica is ...
inclusions that give a similar glittering appearance; the technical term for this optical phenomenon, "
aventurescence In gemology, aventurescence (sometimes called aventurization) 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. Thes ...
", is also derived from the same source.


Production

One original manufacturing process for goldstone was invented in seventeenth-century
Venice Venice ( ; it, Venezia ; vec, Venesia or ) is a city in northeastern Italy and the capital of the Veneto Regions of Italy, region. It is built on a group of 118 small islands that are separated by canals and linked by over 400  ...
by the Miotti family, which was granted an exclusive license by the
Doge A doge ( , ; plural dogi or doges) was an elected lord and head of state in several Italian city-states, notably Venice and Genoa, during the medieval and renaissance periods. Such states are referred to as " crowned republics". Etymology The ...
. Urban legend says goldstone was an accidental discovery by unspecified Italian monks or the product of alchemy, but there is no pre-Miotti documentation to confirm this. A goldstone amulet from 12th- to 13th-century Persia in the collection of the
University of Pennsylvania The University of Pennsylvania (also known as Penn or UPenn) is a private research university in Philadelphia. It is the fourth-oldest institution of higher education in the United States and is ranked among the highest-regarded universitie ...
shows that other, earlier artisans were also able to create the material. 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 In an aqueous solution, precipitation is the process of transforming a dissolved substance into an insoluble solid from a super-saturated solution. The solid formed is called the precipitate. In case of an inorganic chemical reaction leading ...
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 heterogeneous. The best material is near the center or "heart" of the mass, ideally with large, bright metal crystals suspended in a semitransparent glass matrix.


Variations


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
colloid A colloid is a mixture in which one substance consisting of microscopically dispersed insoluble particles is suspended throughout another substance. Some definitions specify that the particles must be dispersed in a liquid, while others extend ...
al copper. The key variable is controlling the colloid size: goldstone has macroscopic reflective crystals; purpurin glass has microscopic opaque particles; copper ruby
glass Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling (quenching) of ...
has submicroscopic transparent nanoparticles. The outer layers of a goldstone batch tend to have duller colors and a lower degree of glittery
aventurescence In gemology, aventurescence (sometimes called aventurization) 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. Thes ...
. 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 In pyrology, flames are affected by the fuel introduced and the oxygen available. A flame with a good oxygen-fuel ratio is called a neutral flame. The color of the flame is semi-transparent purple or blue. This flame is optimal for all intentions, ...
, 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 is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, pr ...
or
manganese Manganese is a chemical element with the symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of industrial alloy use ...
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 is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal. Chromium metal is valued for its high corrosion resistance and hardne ...
oxides rather than the elemental metal, but is otherwise fairly similar.MJ Pelouze,
On A New Aventurine, With Chrome as the Base
. ''Philosophical Magazine and Journal of Science''. 1865, pages 455-6
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

{{commons category, Goldstone

Earliest documentation of goldstone cited as 1626. Gemstones Glass types Glass art