Cristallo is a glass that is totally clear (like rock crystal), without the slight yellow or greenish color originating from iron oxide impurities. This effect is achieved through small additions of manganese oxide. [1] Often Cristallo has a low lime content, which makes it prone to glass corrosion (otherwise known as glass disease).
The invention of Cristallo glass is attributed to Angelo Barovier around 1450. [2]
In addition to common glass making materials manganese, quartz pebbles, and alume catino, a particularly suitable form of soda ash, are used in the making of cristallo glass.
Rather than using common sand, crushed quartz pebbles were used instead. The quartz pebbles were typically from the Ticino and the Adige rivers. The quartz pebbles went through a rigorous screening process before being selected for use in cristallo production. The quartz pebbles had to be free of yellow and black veins and also had to be able to produce sparks when struck with steel.
If the quartz pebbles passed the selection process then the pebbles were heated to the point where the stones began to glow and then placed into cold water. Then the pebbles were crushed and ground.
The typical flux used in the production of cristallo was called alume catino. Alume catino was derived from the ash of the salsola soda and salsola kali bushes that grew in the Levantine coastal region. It was found to contain high and constant amounts of sodium and calcium carbonates, necessary to make workable and chemically stable glass. [3]
The ash of the plants was carefully sieved and then placed into water to be gently boiled with constant mixing. Then the ashen mixture was placed into shallow pans to be dried. The alume catino would repeatedly undergo the boiling and drying process until all of the salt was extracted from the ashes.
The crushed and ground quartz was mixed with the purified alume catino and constantly mixed at high temperatures. The top of the molten batch would then be skimmed off. By skimming the top of the molten glass, unreacted and undissolved chlorides and sulfates in the mixture were removed.
The molten glass would then be ladled into vats of water. The water removed chloride and sulfate impurities from the mixture. The process of remelting and placing the molten mixture into vats of water was repeated several times until the glass-makers were satisfied.
Next the glass was placed into a furnace that was heated to the highest temperature possible and left there for several days. The material was stirred continually to eliminate defects, such as bubbles.
Then the refined mixture was taken, heated and shaped into blocks called frit. The frit was then taken and remelted and skimmed once again in order to remove impurities. The batch then had manganese added to the mixture at this time. The addition of manganese helps to rid the cristallo of any color tints. This step is repeated until the glass-maker is satisfied.
Now the molten mixture is ready to be shaped by glass-makers into pieces of cristalloware.
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.
Sodium carbonate is the inorganic compound with the formula Na2CO3 and its various hydrates. All forms are white, odourless, water-soluble salts that yield alkaline solutions in water. Historically, it was extracted from the ashes of plants grown in sodium-rich soils, and because the ashes of these sodium-rich plants were noticeably different from ashes of wood, sodium carbonate became known as "soda ash". It is produced in large quantities from sodium chloride and limestone by the Solvay process, as well as by carbonating sodium hydroxide which is made using the Chlor-alkali process.
Potassium chlorate is a compound containing potassium, chlorine and oxygen, with the molecular formula KClO3. In its pure form, it is a white crystalline substance. After sodium chlorate, it is the second most common chlorate in industrial use. It is a strong oxidizing agent and its most important application is in safety matches. In other applications it is mostly obsolete and has been replaced by safer alternatives in recent decades. It has been used
Manganese dioxide is the inorganic compound with the formula MnO
2. This blackish or brown solid occurs naturally as the mineral pyrolusite, which is the main ore of manganese and a component of manganese nodules. The principal use for MnO
2 is for dry-cell batteries, such as the alkaline battery and the zinc–carbon battery. MnO
2 is also used as a pigment and as a precursor to other manganese compounds, such as KMnO
4. It is used as a reagent in organic synthesis, for example, for the oxidation of allylic alcohols. MnO
2 has an α-polymorph that can incorporate a variety of atoms in the "tunnels" or "channels" between the manganese oxide octahedra. There is considerable interest in α-MnO
2 as a possible cathode for lithium-ion batteries.
The Leblanc process was an early industrial process for making soda ash used throughout the 19th century, named after its inventor, Nicolas Leblanc. It involved two stages: making sodium sulfate from sodium chloride, followed by reacting the sodium sulfate with coal and calcium carbonate to make sodium carbonate. The process gradually became obsolete after the development of the Solvay process.
Sodium sulfate (also known as sodium sulphate or sulfate of soda) is the inorganic compound with formula Na2SO4 as well as several related hydrates. All forms are white solids that are highly soluble in water. With an annual production of 6 million tonnes, the decahydrate is a major commodity chemical product. It is mainly used as a filler in the manufacture of powdered home laundry detergents and in the Kraft process of paper pulping for making highly alkaline sulfides.
Nicolas Leblanc was a French chemist and surgeon who discovered how to manufacture soda ash from common salt.
Venetian glass is glassware made in Venice, typically on the island of Murano near the city. Traditionally it is made with a soda–lime "metal" and is typically elaborately decorated, with various "hot" glass-forming techniques, as well as gilding, enamel, or engraving. Production has been concentrated on the Venetian island of Murano since the 13th century. Today Murano is known for its art glass, but it has a long history of innovations in glassmaking in addition to its artistic fame—and was Europe's major center for luxury glass from the High Middle Ages to the Italian Renaissance. During the 15th century, Murano glassmakers created cristallo—which was almost transparent and considered the finest glass in the world. Murano glassmakers also developed a white-colored glass that looked like porcelain. They later became Europe's finest makers of mirrors.
Salsola soda, the opposite-leaved saltwort, oppositeleaf Russian thistle, or barilla plant, is a small, annual, succulent shrub that is native to the Mediterranean Basin. It is a halophyte that typically grows in coastal regions and can be irrigated with salt water.
Kali turgidum, commonly known as prickly saltwort or prickly glasswort, is an annual plant that grows in salty sandy coastal soils.
Barilla refers to several species of salt-tolerant (halophyte) plants that, until the 19th century, were the primary source of soda ash and hence of sodium carbonate. The word "barilla" was also used directly to refer to the soda ash obtained from plant sources. The word is an anglicization of the Spanish word barrilla for saltwort plants.
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.
The glassworts are various succulent, annual halophytic plants, that is, plants that thrive in saline environments, such as seacoasts and salt marshes. The original English glasswort plants belong to the genus Salicornia, but today the glassworts include halophyte plants from several genera, some of which are native to continents unknown to the medieval English, and growing in ecosystems, such as mangrove swamps, never envisioned when the term glasswort was coined.
Glass casting is the process in which glass objects are cast by directing molten glass into a mould where it solidifies. The technique has been used since the 15th century BCE in both Ancient Egypt and Mesopotamia. Modern cast glass is formed by a variety of processes such as kiln casting or casting into sand, graphite or metal moulds.
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.
A glossary of terms used in glass art
Medieval stained glass is the coloured and painted glass of medieval Europe from the 10th century to the 16th century. For much of this period stained glass windows were the major pictorial art form, particularly in northern France, Germany and England, where windows tended to be larger than in southern Europe. In some countries, such as Sweden and England, only a small number of original stained windows has survived to this day.
Vitrified sand is sand that has been heated to a high enough temperature to undergo vitrification, which is the melting of the silicon dioxide or quartz that compose common sand. Vitrified sand is a type of natural glass, contrasted with manufactured glass in which soda ash or potash are added to lower the melting point. Pure quartz melts at 1,650 °C (3,002 °F). There are several natural processes that produce more or less melted sand and one man-made form:
The history of glass-making dates back to at least 3,600 years ago in Mesopotamia. However, some writers claim that they may have been producing copies of glass objects from Egypt. Other archaeological evidence suggests that the first true glass was made in coastal north Syria, Mesopotamia or Egypt. The earliest known glass objects, of the mid 2,000 BCE, were beads, perhaps initially created as the accidental by-products of metal-working (slags) or during the production of faience, a pre-glass vitreous material made by a process similar to glazing. Glass products remained a luxury until the disasters that overtook the late Bronze Age civilizations seemingly brought glass-making to a halt.
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