Goldstone is a type of glittering glass made in a low-oxygen reducing atmosphere. The finished product can take a smooth polish and be carved into beads, figurines, or other artifacts suitable for semiprecious stone, and in fact goldstone is often mistaken for or misrepresented as a natural material.
Another common name for the material is aventurine glass, based on the original Italian name avventurina (from avventura, "adventure" or "chance"). It is called "del-roba" (Persian: دلربا) in Persian which means "Charming"; or "monk's gold" or "monkstone" from folkloric associations with an unnamed monastic order.
The material is sometimes incorrectly called sandstone when used in watch dials, and other jewelry, despite its lack of resemblance to the porous, matte texture of the natural stone. It's also confused with Sunstone but apart from the aventurine-like look and the colour, they don't share anything in their structure.
Additionally, "aventurine" glass is one of the few synthetic simulants to provide the eponym for the similar natural stones. The mineral name "aventurine" is used for forms of feldspar or quartz with mica inclusions that give a similar glittering appearance; the technical term for this optical phenomenon, "aventurescence", is also derived from the same source.
One original manufacturing process for goldstone was invented in seventeenth-century Venice by the Miotti family, which was granted an exclusive license by the Doge.[ citation needed ] 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 shows that other, earlier artisans were also able to create the material. [1]
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.[ citation needed ]
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.[ citation needed ]
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.
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. [2]
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).
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 the definition to include substances like aerosols and gels. The term colloidal suspension refers unambiguously to the overall mixture. A colloid has a dispersed phase and a continuous phase. The dispersed phase particles have a diameter of approximately 1 nanometre to 1 micrometre.
Glass is a non-crystalline solid that is often transparent, brittle and chemically inert. It has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics.
A metal is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typically ductile and malleable. These properties are the result of the metallic bond between the atoms or molecules of the metal.
Lustre is the way light interacts with the surface of a crystal, rock, or mineral. The word traces its origins back to the Latin lux, meaning "light", and generally implies radiance, gloss, or brilliance.
Glass-ceramics are polycrystalline materials produced through controlled crystallization of base glass, producing a fine uniform dispersion of crystals throughout the bulk material. Crystallization is accomplished by subjecting suitable glasses to a carefully regulated heat treatment schedule, resulting in the nucleation and growth of crystal phases. In many cases, the crystallization process can proceed to near completion, but in a small proportion of processes, the residual glass phase often remains. Glass-ceramic materials share many properties with both glasses and ceramics. Glass-ceramics have an amorphous phase and one or more crystalline phases and are produced by a so-called "controlled crystallization" in contrast to a spontaneous crystallization, which is usually not wanted in glass manufacturing. Glass-ceramics have the fabrication advantage of glass, as well as special properties of ceramics. When used for sealing, some glass-ceramics do not require brazing but can withstand brazing temperatures up to 700 °C. Glass-ceramics usually have between 30% [m/m] and 90% [m/m] crystallinity and yield an array of materials with interesting properties like zero porosity, high strength, toughness, translucency or opacity, pigmentation, opalescence, low or even negative thermal expansion, high temperature stability, fluorescence, machinability, ferromagnetism, resorbability or high chemical durability, biocompatibility, bioactivity, ion conductivity, superconductivity, isolation capabilities, low dielectric constant and loss, corrosion resistance, high resistivity and break-down voltage. These properties can be tailored by controlling the base-glass composition and by controlled heat treatment/crystallization of base glass. In manufacturing, glass-ceramics are valued for having the strength of ceramic but the hermetic sealing properties of glass.
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. In aventurine quartz chrome-bearing fuchsite produces a green stone, and various iron oxides produce a red stone.
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.
Strontium titanate is an oxide of strontium and titanium with the chemical formula SrTiO3. At room temperature, it is a centrosymmetric paraelectric material with a perovskite structure. At low temperatures it approaches a ferroelectric phase transition with a very large dielectric constant ~104 but remains paraelectric down to the lowest temperatures measured as a result of quantum fluctuations, making it a quantum paraelectric. It was long thought to be a wholly artificial material, until 1982 when its natural counterpart—discovered in Siberia and named tausonite—was recognised by the IMA. Tausonite remains an extremely rare mineral in nature, occurring as very tiny crystals. Its most important application has been in its synthesized form wherein it is occasionally encountered as a diamond simulant, in precision optics, in varistors, and in advanced ceramics.
Smart glass, also known as switchable glass, dynamic glass, and smart-tinting glass, is a type of glass that can change its reflective properties to prevent sunlight and heat from entering a building and to also provide privacy. Smart glass for building aims to provide more energy-efficient buildings by reducing the amount of solar heat that passes through glass windows.
In materials science, the sol–gel process is a method for producing solid materials from small molecules. The method is used for the fabrication of metal oxides, especially the oxides of silicon (Si) and titanium (Ti). The process involves conversion of monomers into a colloidal solution (sol) that acts as the precursor for an integrated network of either discrete particles or network polymers. Typical precursors are metal alkoxides. Sol-gel process is used to produce ceramic nanoparticles.
Ceramic engineering is the science and technology of creating objects from inorganic, non-metallic materials. This is done either by the action of heat, or at lower temperatures using precipitation reactions from high-purity chemical solutions. The term includes the purification of raw materials, the study and production of the chemical compounds concerned, their formation into components and the study of their structure, composition and properties.
A self-cleaning or pyrolytic oven is an oven which uses high temperature to burn off leftovers from baking, without the use of any chemical agents. The oven can be powered by domestic (non-commercial) electricity or gas.
A frit is a ceramic composition that has been fused, quenched, and granulated. Frits form an important part of the batches used in compounding enamels and ceramic glazes; the purpose of this pre-fusion is to render any soluble and/or toxic components insoluble by causing them to combine with silica and other added oxides. However, not all glass that is fused and quenched in water is frit, as this method of cooling down very hot glass is also widely used in glass manufacture.
Glass-to-metal seals are a type of mechanical seal which joins glass and metal surfaces. They are very important elements in the construction of vacuum tubes, electric discharge tubes, incandescent light bulbs, glass-encapsulated semiconductor diodes, reed switches, glass windows in metal cases, and metal or ceramic packages of electronic components.
Forest glass is late medieval glass produced in northwestern and central Europe from approximately 1000–1700 AD using wood ash and sand as the main raw materials and made in factories known as glasshouses in forest areas. It is characterized by a variety of greenish-yellow colors, the earlier products often being of crude design and poor quality, and was used mainly for everyday vessels and increasingly for ecclesiastical stained glass windows. Its composition and manufacture contrast sharply with Roman and pre-Roman glassmaking centered on the Mediterranean and contemporaneous Byzantine and Islamic glass making to the east.
Solid is one of the four fundamental states of matter along with liquid, gas, and plasma. The molecules in a solid are closely packed together and contain the least amount of kinetic energy. A solid is characterized by structural rigidity and resistance to a force applied to the surface. Unlike a liquid, a solid object does not flow to take on the shape of its container, nor does it expand to fill the entire available volume like a gas. The atoms in a solid are bound to each other, either in a regular geometric lattice, or irregularly. Solids cannot be compressed with little pressure whereas gases can be compressed with little pressure because the molecules in a gas are loosely packed.
A colloidal crystal is an ordered array of colloidal particles and fine grained materials analogous to a standard crystal whose repeating subunits are atoms or molecules. A natural example of this phenomenon can be found in the gem opal, where spheres of silica assume a close-packed locally periodic structure under moderate compression. Bulk properties of a colloidal crystal depend on composition, particle size, packing arrangement, and degree of regularity. Applications include photonics, materials processing, and the study of self-assembly and phase transitions.
Glass coloring and color marking may be obtained in several ways.
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. Purpurin is somewhat harder than normal glass but can be easily cut and polished. Its red color is permanently lost upon smelting. The material bears some resemblance to goldstone.
Crystallization of polymers is a process associated with partial alignment of their molecular chains. These chains fold together and form ordered regions called lamellae, which compose larger spheroidal structures named spherulites. Polymers can crystallize upon cooling from melting, mechanical stretching or solvent evaporation. Crystallization affects optical, mechanical, thermal and chemical properties of the polymer. The degree of crystallinity is estimated by different analytical methods and it typically ranges between 10 and 80%, with crystallized polymers often called "semi-crystalline". The properties of semi-crystalline polymers are determined not only by the degree of crystallinity, but also by the size and orientation of the molecular chains.
