What is Ftda glass



Glass (from Germanic glasa “The shiny, shimmering”, also for “amber”) is an amorphous, non-crystalline solid. Materials that are referred to as glass in everyday life (for example drinking glasses and window glasses, television panes and light bulbs) are only a part of the variety of glasses.

definition

Glass is an amorphous substance. Glass is usually produced by melting, but glass can also be formed by heating sol-gel and by shock waves. Thermodynamically, glass is referred to as a frozen, supercooled liquid. This definition applies to all substances that are melted and cooled accordingly quickly. This means that when the melt solidifies to form crystal nuclei, there is not enough time left for the crystallization process. The solidifying glass quickly becomes too solid to allow crystal formation. The transformation area, that is the transition area between the melt and the solid, is around 600 ° C for many types of glass.

Despite the undefined melting point, glass is a solid. Even if it deformed under long-term force, it should not be called liquid. The slow deformation under a constant force also occurs in crystalline solids and is known as creep. Reports from flowing church windows can not be confirmed and the idea of liquid glass seems to be due to a wrong translation.

   

Because of their thermodynamic properties (amorphous structure, glass transition, etc.), plastics such as Plexiglas also fall into the category of glasses, although their chemical composition is completely different from that of silicate glasses.

The most meaningful property of glass in common parlance is its optical transparency. The optical properties are as varied as the number of glasses. In addition to clear glasses that allow light to pass through in a wide band, it is possible to block the transparency by adding special materials to the melt. For example, optically clear glasses can be made impenetrable for infrared light, the thermal radiation is blocked. The most well-known control of permeability is the coloration. A wide variety of colors can be achieved. On the other hand, there is opaque glass that is opaque due to its main components or the addition of opacifiers.

Utility glass has a density of approx. 2500 kg / m³ (2.5 g / cm³). The mechanical properties vary greatly. The fragility of glass is proverbial. The breaking strength is largely determined by the quality of the surface. Glass is largely resistant to chemicals. Hydrofluoric acid is an exception; it dissolves the silicon dioxide and converts it to hexafluorosilicic acid. At room temperature, glass has a high electrical resistance, which, however, drops sharply with increasing temperature, unless it is pure quartz glass.

properties

structure

 

Although glass is one of the oldest materials known to mankind, many questions about the atomic structure and its structure are still unclear. The meanwhile generally accepted interpretation of the structure is the network hypothesis, which was put forward by Zachariasen in 1932. This means that basically the same bonding states exist in the glass as in the crystal. In the case of silicate glasses, in other words, in the form of SiO4-Tetrahedra.

As the two-dimensional images of quartz and quartz glass show, the difference lies in the regularity of the structure - here a lattice and there a network. The fourth oxide bond, which points into the third dimension, is not shown for the sake of clarity. The bond angles and distances in the glass are not regular and the tetrahedra are distorted. The comparison shows that glass only has a short-range order in the form of tetrahedra, but has no crystalline long-range order. This lack of long-range order is also responsible for the very difficult analysis of the glass structure. In particular, the medium-range analysis, i.e. the connections of several basic forms (here the tetrahedra), is the subject of current research and is one of the greatest problems in physics today.

The material that determines this basic structure of the glass is called a network builder. In addition to the silicon oxide mentioned, other substances such as boron oxide and non-oxidic substances such as arsenic sulfide can also be network formers. One-component glasses are the exception, however, and quartz glass is the only one that is economically significant. Other substances are integrated differently into the network structure. A distinction is made here between network converters and stabilizers.

Network converters are built into the framework formed by the network builder. For ordinary glass for everyday use - lime-alkali glass (but the narrower term is more common Soda lime glass) - these are sodium or potassium oxide and calcium oxide. These network converters tear open the network structure. In the process, bonds of the bridging oxygen in the silicon oxide tetrahedra are broken. Instead of the atomic bond with the silicon, the oxygen forms an ionic bond with an alkali atom.

Intermediate oxides such as aluminum oxide and lead oxide can function as network formers and converters. However, they are not capable of glass formation on their own.

Transition from the melt to the solid glass

In contrast to the cooling of crystalline materials, the transition from liquid melt to solid is gradual in glass. Therefore one does not speak of enamel herePoint but from a transformationArea. In the course of cooling, the viscosity of the material increases sharply. This is the external sign of an increasing internal structure. Since this structure does not have a regular pattern, the state of the melt in the transformation area, like that of the solidified glass, is called amorphous. At the cool end of the transformation area there is a thermodynamic transition that is characteristic of glass and therefore bears the name glass transition. On it, the melt changes into the solid, glass-like state that the glass also shows when it cools down further. The glass transition is characterized by a sudden change in the coefficient of thermal expansion and a decrease in the specific heat C.p out.

This sequence of transformation area and glass transition is characteristic of all glasses, including those made of hydrocarbons like Plexiglas. The amorphous, viscous state of the melt in the transformation area is used for the processing of glass by glass blowing. It allows any deformation without surface tension and gravity causing the workpiece to melt immediately.

Adjustment of the glass properties

Glass properties can be determined by means of statistical analysis of glass databases such as B. from SciGlass®[1] or Interglad®[2] determined and optimized. If the desired glass property is not related to crystallization (e.g. liquidus temperature) or phase separation, simple linear regression analysis can be used with the aid of polynomial equations of the first to third order. Below is a second order equation as an example, where C. the concentrations of the glass components such as Na2Represent O or CaO. The bValues ​​are variable coefficients, and n is the number of all glass components. The main glass component SiO2 is excluded in the equation shown and is given by the constant bO considered. Most of the terms in the example equation can be neglected due to correlation and significance analysis. More details and applications are available at [3].


The liquidus temperature was modeled by C. Dreyfus and G. Dreyfus using neural networks regression. [4]


In industry it is often necessary to optimize several glass properties, including production costs, at the same time. To do this, proceed as follows in a spreadsheet program:

  1. List of the desired properties;
  2. Input of models for reliable calculation of properties, including a formula for calculating production costs;
  3. Calculating the squares of the differences between desired and calculated properties;
  4. Minimizing the sum of squares using the solver option[5] in the spreadsheet program, where the variables are set by the glass composition in percentages by weight or moles. (Aside from Microsoft Excel, not all spreadsheet programs have the solver option[5].)

It is possible to weight the desired properties differently. [6]

Glass type SiO2Al2O3N / A2OK2OMgOCaOB.2O3PbOTiO2F.AsSeGeTe
Quartz glass100 %
Soda lime glass 72 %2 %14 %10 % -
Float glass72 %1,5 %13,5 %3,5 %8,5 %
Lead crystal glass60 %8 %2,5 %12 % 17,5 %
Laboratory glass 80 %3 %4 %0,512,5 %
E-glass54 %14 %4,5 %17,5 %10 %
E-mail40 %1,5 %9 %6 %1 %-10 % 4 % 15 % 13 %
Chalcogenide glass 1 12 % 55 % 33 %
Chalcogenide glass 2 13 % 32 % 30 % 25 %

Glass aggregates include:

Glass staining and discoloration

Most types of glass are produced with other additives to influence certain properties, such as their color. To color the glass, metals are added to the glass melt in the form of nanoparticles (around 0.1%). The most frequently used metals are gold and silver with a grain size of a few nanometers. Another decisive factor is the shape of the particles, e.g. B. prolate, spherical or oblate. The different colors in reflection or transmission are influenced by the nanoparticles.

Metal oxides are mainly used to discolor glasses caused by contamination of their raw materials. Basically, the complementary color is used to remove color casts. Decolorizers were called glassmaker's soaps.

 

  • Iron oxides: Depending on the valency of the iron ion, they are colored green-blue-green or yellow and, in combination with brownstone, yellow and brown-black.
  • Copper oxides: bivalent copper colors blue, monovalent copper colors red, this is the result Copper ruby ​​glass.
  • Chromium oxide: Used in conjunction with iron oxide or on its own for green coloring.
  • Uranium oxide: Gives a very fine yellow or green color (Annagelbglas- or Anna green glass) with green fluorescence under UV light. Such glasses were mainly made in the Art Nouveau period. In England and America this type of glass is also known as uranium glass or vaseline glass known. Due to the radioactivity of uranium, it is no longer used today.
  • Cobalt oxide: has an intense blue color and is also used for decolorization. Together with aluminum oxide, it is found in the deep blue as cobalt aluminate Cobalt glass in front.
  • Nickel oxide: violet, reddish also for the gray coloring and for discoloration
  • Manganese oxide (brown stone) as glassmaker's soap to remove the green cast (by absorbing the complementary colors)
  • Selenium oxide: colors pink and red, the pink color is called Rosalin while the red is referred to as Selenium ruby referred to as.
  • Silver: produces a fine silver yellow
  • Indium oxide: yellow to amber orange
  • Neodymium: pink to purple, lavender.
  • Praseodymium: green
  • Samarium: yellow
  • Europium: intense pink
  • Gold: Is only dissolved in aqua regia and turns ruby ​​red, one of the most expensive glass colors gold purple.

Classification of glasses

 

By type of genesis: Next artificial can also be found natural glasses:Obsidian and pumice stone are of volcanic origin, impact glasses and tektites are created by a meteorite impact, fulgurite by lightning strikes, trinitite by an atomic bomb explosion and the frictionite köfelsite by landslides. These glasses are made by melting sand. A crystal lattice can also lose its structure through the action of a shock wave and become an amorphous body. This diaplectic glass includes maskelynite, which is made from feldspar. It is also possible to produce glass without melting using the sol-gel process. An example of this are silicate aerogels.

According to the type of "chemism": In addition to soda-lime glass, which corresponds to normal glass for use, there is quartz glass made of pure silicon dioxide, lead glass for e.g. B. crystal drinking glasses, television funnels and optical lenses. The lead in the glass shields electromagnetic radiation, has a high refractive index and is evenly dispersed. Water glass is soluble in water. Borosilicate glass is particularly chemically resistant and is used in laboratory equipment, cookware, but also optical glasses. Boron phosphate glass (boron trioxide, phosphorus pentoxide) and aluminosilicate glasses are further special glasses. The group of non-oxidic glasses includes fluoride glasses and chalcogenide glasses in infrared optics. Glass ceramics have to be understood as a special case in this classification. It is produced as glass and recrystallization is partially achieved through the heat treatment. Strictly speaking, it is no longer glass, but a mixed glass-crystal body.

According to the basic shape of the product and the production process: The glass industry is usually divided into hollow glass, flat glass and special glass production. Hollow glass refers to bottles and canning jars. These mass products are blown by machine. Higher quality products are pressed. This includes glass blocks and drinking glasses. A special production process is necessary for incandescent lamps, as well as for tubular glass. Flat glass is called float glass or rolled glass, depending on the production process. The basic product is a pane of glass. End products are e.g. B. automotive glass, mirrors, tempered glass, laminated glass. Fiberglass includes fiber optic cables, glass wool and is also used in fiberglass reinforced plastics. Optical glasses are lenses for microscopes and binoculars. Hand-blown glasses practically only exist in the arts and crafts, as well as in expensive vases and wine glasses.

According to their traditional trade names: Antique glass, diatret glass, flint glass (lead glass as optical glass), hyalith glass (opaque glass, used in the 19th century for table and pharmaceutical glass), crown glass (optical glass), cryolite glass (opaque, white fluoride glass).

According to their brand names as a generic term: Ceran (glass ceramic for e.g. hobs), Jenaer Glas (heat-resistant borosilicate glass) both from Schott and Pyrex (borosilicate glass) from Corning are synonymous in the Anglo-Saxon language area Jena glass.

See also:List of glasses

Production process

mixture

     

The following raw materials are used for the production of soda-lime glass, which makes up approx. 90% of the amount of glass produced:

  • Quartz sand as almost pure SiO2- Support for network building. It is important that the sand only contains a small amount of Fe2O3 may own (
  • Sodium carbonate (mineral: natrite; Na2CO3) serves as a sodium oxide carrier, which serves as a network converter and as a flux, and the melting point of the SiO2 lowers. Carbon dioxide is released in the melt and dissolves from the glass as a gas. Sodium can also be added to the melt as nitrate or sulfate.
  • Potash (K2CO3) supplies potassium oxide for the melt, which, like sodium oxide, serves as a network converter and flux.
  • Feldspar (NaAlSi3O8) carries in addition to SiO2 and well2O clay (Al2O3) into the mix. This leads to an increase in the glass hardness.
  • Lime acts as a network converter and increases the strength of the glasses. Pure CaO has a melting point that is too high, so CaCO3 is used. When it melts, it converts to carbon dioxide and calcium oxide. A moderate addition (10–15%) of CaO increases the hardness.
  • Dolomite is a carrier for CaO and MgO. Magnesium oxide has properties similar to calcium oxide on the melt.
  • Old glass or cullet from broken production are also returned to the batch - but only used in the container glass industry, where their share can be up to 90%. In addition to saved raw materials, this is noticeable in the lower energy consumption, since cullet melts more easily than the batch. Problems with waste glass recycling are poor color separation, foreign components such as metals, ceramics or special glasses. The foreign substances cause glass defects due to incomplete melting and damage to the glass melting tank, as metals eat into the refractory floor.

Red lead, borax, barium carbonate and rare earths are also used for special glasses.

melt

The glass melt consists of different phases: The rough melt starts with the melting of the mixture. This includes rough melt and homogenization. After the solid components have melted, there is refining, in which the gases in the melt are expelled. This is followed by the protrusion of the glass, in which the material is cooled down for further shaping.

In the case of batch-type day tubs and port furnaces, all these steps take place one after the other in the same basin. This historical production process only takes place today in the case of handicraft production and special, optical glasses in small quantities. Only continuously operating ovens are used on an industrial scale. Here the sequence of the above steps is not temporally but spatially separated. The amount of glass removed corresponds to that of the batch added.

The batch is fed into the melting tank with a feeding machine. At temperatures of approx. 1480 ° C, the various components slowly melt. The movement of convection in the glass bath creates homogeneity.This can be supported by bubbling, the injection of air or gases into the melt.

In the refining area, which immediately follows the melting area and is often separated from it by a wall in the melt, bubbles remaining in the melt are expelled. Due to the high viscosity of the melt, this happens only very gradually, and the temperatures required are just as high as in the melting range. Since the refining is decisive for the quality of the glass, there are various measures to support this.

The structurally clearly separated working tub adjoins the lautering area. Since lower temperatures are required for shaping than for melting and refining, the glass must protrude beforehand. This is why one also speaks of a standing trough. The channel that connects the melting tank and working tank is called the flow and works according to the siphon principle. In the case of flat glass tanks, the melting and working tanks are only separated by a constriction, since a flow would create an optical unrest in the finished product.

The glass continues to flow from the working tub to the point of removal. In the production of hollow glass, these are the risers or feeders. Here, drops are directed into the glass machines below. With flat glass, the glass flows over the lip into the float bath.

Shaping

Glass is shaped differently depending on the product. A distinction is made primarily between glasses that are pressed, blown, jetted, spun or rolled.

 

  • Hollow glass is made in several processes by pressing, blowing, sucking and combinations of these techniques. The IS machine dominates here, operating in the blow-and-blow or press-and-blow process. For higher-quality tableware, press-blow processes are used, which work in the shape of a carousel.
  • Fiberglass are produced by spinning in the so-called TEL process.
  • Flat glass is manufactured, drawn, rolled or cast using the float process
  • Tubular glass has been manufactured using a continuous drawing process since 1912

cooling

Relaxation cooling

In every glass object, mechanical stresses arise during shaping as a result of differences in expansion in the material. These stresses can be measured with optical stress testers (stress birefringence). The susceptibility to stress depends on the expansion coefficient of the respective glass and must be thermally compensated.

For each glass you can choose between the upper cooling temperature (viscosity of 1013 mPas) and a lower cooling temperature (1018 mPas), usually between 550 ° C and 350 ° C, specify a cooling range. The stresses are reduced by a defined slow cooling in the cooling area, the tempering.

The time in which a glass object can pass through the cooling area is largely dependent on the temperature to be bridged and the thickness of the object, depending on the type of glass. In the hollow glass area, these are between 30 min and 100 min; for large optical lenses with a diameter of 1 m and more, a slow cooling of a year may be necessary in order to avoid visible tension and thus image distortion of the lens.

The controlled temperature reduction can be carried out with different ovens. A distinction is made between periodic cooling furnaces and continuous cooling tracks. Cooling furnaces are only suitable for special productions and very small batches, as the furnace has to be brought back up to temperature each time the workpieces are removed. Cooling tracks are used industrially. Here the production is slowly transported on steel mats (hollow glass) or rolls (flat glass) through stepped heated furnace segments.

 

Surface finishing

  • The finest metal coatings can be applied by chemical and physical vapor deposition. Most window and car glasses are provided with coatings that are impervious to infrared light in this way. The heat radiation is reflected and interior rooms are less heated by solar radiation. At the same time, heat losses are reduced in winter without significantly impairing transparency.
See also: Ikora
  • The coating with dielectric material, which is itself transparent, but has a refractive index that differs from that of the glass substrate, both reflective and anti-reflective coatings are possible. This is used in the manufacture of spectacle lenses and lenses for cameras in order to reduce annoying reflections. For scientific purposes, layers are made that reflect more than 99.9999% of the incident light of a certain wavelength. Conversely, it can also be achieved that 99.999% of the light pass through the surface.
  • The surface can be roughened by sandblasting or with hydrofluoric acid so that the light is strongly scattered. It then appears milky and no longer transparent, but very little light is still absorbed. Therefore this technique is often used for lampshades or for opaque windows.

History of glass production

Early and ancient times

 

Natural glass such as obsidian has been used for tools such as wedges, blades, scrapers and drills since the earliest times because of its great hardness and sharp breakage. However, unlike artificially produced glass, obsidian cannot be melted or colored using ancient means.

Whether glass manufacture was invented in Mesopotamia, Egypt or on the Levant coast cannot be said with absolute certainty. The oldest regularly occurring glass finds come from Mesopotamia, and Egyptian sources point to an import from the east for the initial phase of glass use in Egypt. The oldest textual mention comes from Ugarit and is dated around 1600 BC. dated. The oldest finds are the Nuzi pearls, the oldest glass vessel that can be safely dated is a chalice that bears the name of the Egyptian pharaoh Thutmose III. carries and around 1450 BC BC originated. The chalice is now in the State Museum of Egyptian Art in Munich.

Glass has been in Egypt since around 1400 BC. processed into vessels, the place of manufacture of this earliest glass is unknown. The best-known processing technique is based on the production of hollow vessels by wrapping softened glass rods around a porous ceramic core, which is then scraped out. The best finds on this are from the excavations of Flinders Petrie from Amarna. The so far only known Bronze Age glassworks in which glass was made from its raw materials dates back to the Ramesside period and was discovered in the late 1990s during excavations of the Roemer and Pelizaeus Museum (Hildesheim) under the direction of Edgar Pusch in the eastern Nile Delta in Qantir -Piramesse found. Investigations provided information about the melting process. Quartz rock was crushed, mixed with plant ash containing soda, poured into a jug and melted into a frit at about 800 ° C. After cooling, this frit was presumably crushed and melted in a second melt in specially manufactured crucibles at 900 to 1100 ° C. to form an 8 to 10 cm high bar with a 10 to 14 cm diameter. The glass was colored black, violet, blue, green, red, yellow or white by adding metal oxides. A specific connection between glass production and metal extraction cannot be proven despite the similar temperatures. The colored raw glass was delivered in bar form to the further processing workshops, which made monochrome and polychrome objects from it. Such glass bars were found in the shipwreck of Uluburun near the Turkish city of Bodrum, which dates back to the 14th century BC. is dated. The first known recipe comes from the library of the Assyrian King Ashurbanipal, which dates back to around 650 BC. is dated: Take 60 parts of sand, 180 parts of seaweed ash and 5 parts of chalk and you will get glass. At that time, a lot more glass was being processed, and a new glass melting technique was developing.

 

Pliny the Elder describes in the Historia naturalis the manufacture of the glass. Chemical analyzes and findings of experimental archeology have confirmed Plinus in many questions. In Roman times, glass was melted with river sand and baking soda from Egypt. This Egyptian natron was mined at Wadi Natrun, a natural natron lake in northern Egypt, and exported by the Phoenicians to the Mediterranean via Alexandria. It contained more than 40% sodium oxide and up to 4% lime, so it was an ideal flux. Pliny continues to write about glass sand deposits in Italy, Hispania and Gaul, but none of these places developed such significant glass production as on the Palestinian coast between Acre and Tire and in the Egyptian glassworks around Wadi Natrun near Alexandria.

Emperor Diocletian laid down in 301 AD. fixed prices for a whole range of products, including raw glass. A distinction was made judaicum and alexandriumthe latter being more expensive and likely discolored glass. At that time, glass production was essentially still divided into primary and secondary workshops. In the primary workshops, raw glass was melted in large melting tanks, which was then delivered to the secondary workshops, where it was melted down in crucibles and processed. In Bet Eli’ezer in what is now Israel, 17 glass melting tanks, each 2 mx 4 m in size, were uncovered. After the mixture had been placed in the tub, the furnace was bricked up and fired for 10 to 15 days. Eight to nine tons of blue or green raw glass were melted in just one operation. After the furnace had stopped and had cooled down, the vault of the furnace was removed, the glass block pried out and the raw glass sent for further processing. A shipwreck from the 3rd century found on the southern French coast had more than 3 tons of raw glass loaded. In Egypt, raw glassworks were found that reached back into the 10th century. The Egyptians used antimony to discolor, so they were able to produce colorless, transparent glass.

The secondary glass works were widespread throughout the Roman Empire and produced hollow glass, flat glass and mosaic stones. The raw glass was melted in a crucible and taken out of the furnace with the pipe in its viscous state and processed. The glass on the pipe could be inflated, which enabled the manufacture of larger vessels and new shapes. Until then, glass was used for pearls, perfume bottles and drinking bowls, but container glass in particular spread in the Roman Empire - in contrast to the usual clay, wood, metal or leather containers, glass is tasteless - as well as carafes for serving and in late antiquity Drinking glasses. The first window glasses were found in Aix-en-Provence and Herculaneum. The finds have sizes of 45 cm × 44 cm and 80 cm × 80 cm. However, nothing is known about the manufacturing process. The cylinder blow molding process and the casting technique are considered here.

Middle Ages and Modern Times

In the early Middle Ages, wherever the Romans had withdrawn, the Teutons produced glass that seamlessly followed the Germanised late antiquity of forms. Today it is assumed that Roman glasses that were still in existence for Franconian glass were recycled.

 

Forest glass

See also main article forest glass.

With “de diversis artibus” by the Benedictine monk Theophilus Presbyter, we have a longer written source available for the first time, which describes glass production, the blowing of flat glass and hollow glass as well as furnace technology. Theophilus, who was probably in Constantinople, mixed ashes from dried beech wood with sifted river sand in a ratio of 2: 1 and dried this mixture in the oven with constant stirring so that it could not melt or stick together for a day and night. This frit was then placed in a crucible and melted into glass in one night under high heat. This text, which was probably written in Cologne at the beginning of the 12th century, may form the basis for the Gothic church windows and also for the forest glass. The vegetable ash with all its impurities also provided part of the lime that was necessary for the production of good glass. In order not to have to transport the enormous amount of wood that was necessary for firing the stoves and even more for ash extraction over long distances, the glassworks were set up in remote forest areas. These forest glassworks mainly produced glass for the urban population, which was colored green by the sand contaminated with iron oxide.

In Georgius Agricola's “de re metalica” there is a brief description of glass art. He lived in Venice from 1524 to 1527 and was probably allowed to visit the island of Murano, as the detailed descriptions of the ovens suggest. Transparent stones are named as raw materials, i.e. rock crystal and white stones, i.e. marble, which are burned in the fire and crushed in the stamping mill and then brought into the form of coarse grains and then sieved. He also cites table salt, magnetic stone and soda. Table salt and magnetic stone are rejected as useless by later authors, marble and soda were found in altars and in Milan; However, they are not available in Germany, just a hint: “salt that is represented from lye” points to a Venetian secret.

The glass melting furnaces of the Waldglashütten and Venice were harbor furnaces; they were egg-shaped constructions made of clay bricks mixed with fired chamotte, 3 m in diameter and up to 3 m high. The firing room was on the lower floor with one or two semicircular openings for wood to be thrown in. In the middle, the flames broke through a large round opening into the second floor, where the harbors stood. This approximately 1.20 m high room was provided with oven gates measuring 20x20 cm all around, through which the mixture could be inserted and the glass removed. On the upper floor, which was connected to the smelting room through a small opening, was the cooling furnace, which was only 400 ° C. The cooling furnace was provided with a small opening through which finished workpieces could be entered. In the evening, the hole between the melting room and the cooling room was closed with a stone so that the glass could cool down overnight.

Venice

At the beginning of the Venetian glass tradition there was probably the trade in Byzantine glass products, which were imported and exported to all of Europe as early as the 10th century. The first glassmakers can be found in the registers of the 11th century. They are called "phiolarius", bottle makers. A merchant ship wrecked on the south coast of Turkey, which sank around 1025, transported no less than 3 tons of raw glass that came from Caesarea in Palestine. Whether it was intended for Venice cannot be said with certainty, but it is obvious. By 1295, all glassmakers were settled on the island of Murano and their freedom of travel was restricted by law. On this island, cut off from the world, Angelo Barovier, who lived in the middle of the 15th century, was able to reveal the secret of discoloration and was the first to produce clear, clear glass in Europe. The “crystallo”, a soda-lime glass that was decolorized with manganese oxide, should establish the world fame of the Venetian glass. The soda was imported from the Levant or Alexandria, leached and boiled until a pure salt was created. Pure glass sand from the Ticino river or burnt marble were used as sand. Another Venetian rediscovery is the “lattimo” (milk glass), an opaque white glass that was tarnished with tin oxide and bone ash, which mimicked Chinese porcelain.

It is only a little flawlessly preserved as authentically Venetian origin verifiable Renaissance glass. The rich variety of its shapes and decors is mainly revealed in still life painting. As a glass à la façon de Venise, the Venetian style found access to the countries north of the Alps, despite all attempts by the Republic of Venice to keep its art secret. Extensive collections have been preserved in Germany, the provenance of which can often only be ascertained indirectly and no longer clearly.

For this chapter see also: Glass production 1550-1700, pdf, 1.1 Mb

Baroque glass

Baroque chopped glass mainly from Bohemia and Silesia, but also Nuremberg, Brandenburg and Saxony, and more rarely Thuringia, Hesse, Northern Germany and the Netherlands outstripped Venetian glass from the 18th century. The Venetians did not master the art of cutting and grinding glass.

The shapes with foot, baluster shaft and thin-walled cupa were similar to the colorless Venetian glass, but without wings. The novelty of this art was the finely elaborated picture scenes cut into the wall. The topics were varied. Hunting scenes were common, landscapes, but also allegorical figures with inscriptions, flower and leaf ornaments.

For the first time in the history of European glass art, individual artists can be identified in the 18th century: Christian Gottfried Schneider shaped the glass cutting in Silesia like Martin Winter that of Potsdam, Johann Christoph Kießling worked for August the Strong, David Wolff in the Netherlands.

Occasionally, the baroque cut glasses have gilding on the base, shaft or on the edge of the lip. If the motifs are gilded, one speaks of intermediate gold glasses. Gold leaf foils were put on and the motifs were erased.

From porcelain painting comes the technique of black solder painting, which in another context was already known in the Middle Ages. Johann Schaper and Ignaz Preissler shaped this art in Nuremberg and Silesia, Bohemia and Saxony.

A rural finishing technique for baroque glass is enamel painting. It is mainly found on glass for use in rural areas (e.g. beer mugs from rifle clubs and schnapps bottles). The motifs match the provenance: farmer with cattle and farm implements, tavern scenes, playing cards, sayings. In Bohemia, enamel painting is also made on opaque milk glass, which brings this technique close to porcelain painting.

Window glass

Although finds already show the use of window glass in the Roman Empire and St. Peter and Santa Maria in Rome showed window glazing as early as the 9th century, a wider use is only proven with the emerging Gothic in the 12th century.

Cylinder stretching process I ...

 

In the moon glass process, which is documented in Rouen in 1330, a glass drop is blown into a ball with a glassmaker's pipe. This was blown off the pipe and attached to a metal rod on the opposite side with a drop of liquid glass. The ball was brought back to temperature for further processing. At around 1000 ° C, the glass was soft enough to be thrown into the shape of a plate by centrifugal force: the ball opened around the hole to which the pipe was previously attached. This technique produced glass plates with a diameter of approx. 1.20 m. Then the outer edge was cut into rectangles. These were used as e.g. B. Church glass with lead frames. The middle piece with the connection point of the throwing rod is called Butze and was used for slug disks with a diameter of 10–15 cm.

 

The rolled glass process was first documented in 1688 in Saint Gobain, the nucleus of today's global corporation of the same name. Molten glass is poured onto the roller table, distributed and finally rolled. In contrast to the previously mentioned methods, a uniform thickness was achieved here. For the first time, pane sizes of 40 inches × 60 inches were also possible, which was used for the production of mirrors. However, the uneven surface causes problems. Window glass made by this manufacturing process is often blind and mirror glass can only be achieved by laborious cold polishing.

Cylinder stretching method II ...

Industrialization and automation

Important events in the development of the glass industry

Generally

  • 1856 First glass furnace with regenerative firing by Friedrich Siemens
  • 1847 Introduction of metal molds in hollow glass production (Joseph Magoun)
  • 1867 Continuous furnace from Friedrich Siemens
  • 1882 Ernst Abbe and Otto Schott found glass works for special optical glasses in Jena

Flat glass

 

Around 1900 the American John H. Lubbers developed a process for cylinder production. These could reach a diameter of 80 cm and were up to 8 m (!) High. The cylinder was cut open and flattened. However, the process was very cumbersome, and in particular the turning of the cylinder into a horizontal position caused difficulties.

A far-reaching patent was to follow from Emile Fourcault in 1904. The Fourcault process named after him for the manufacture of drawn glass. The glass is removed continuously. A pubic nozzle lies in the liquid melt. By pulling it up through a cooling duct to a height of approx. 8 m, it can be cut to size at the top. The thickness of the glass can be adjusted using the pulling speed. It came into use from 1913 and was a great improvement.

The American Irving Wightman Colburn patented a process based on this in 1905. The glass ribbon was diverted into a horizontal cooling channel for better handling. An attempt was made to master the process with its own factory until 1912, but was ultimately unsuccessful, so that bankruptcy was filed. The patent went to the Toledo Glass Company. In 1917 the so-called Libbeys-Owens process came into industrial use. The advantages over the Fourcault process lay in the simpler cooling. On the other hand, several drawing machines were able to work on a glass melting tank. Since the cooling furnace could be of any length, this process achieved about twice the production speed. In the period that followed, both procedures existed in parallel. In 1928 the Plate Glass Company improved the advantages of the Fourcault and Colburn processes; With the Pittsburg process, she achieved a significant increase in production speed.

 

In 1919 Max Bicheroux took the decisive step in the manufacture of cast glass. The liquid glass mass was formed into a glass ribbon between cooled rollers, cut into sheets while still heated and cooled in ovens. With this method, the pane sizes of 3 m × 6 m that are still common today were achieved.

1923 Pilkington and Ford: continuous rolled glass for automotive glass.

1902 William E. Heal's patent on the float process, which goes back to an idea by Henry Bessemer.

1959 The Pilkington company is the first to overcome the technical problems of float glass production. This principle revolutionized flat glass production and became the general standard in the 1970s.

Hollow glass

In the early 19th century, new mechanical aids were used to blow glasses. Shapes were used that already had a relief as a negative. The blowing pressure pushes the glass into the cavities and the workpiece takes on its shape. However, the glassmaker's lung power is not high enough for deeper reliefs, so mechanical aids were introduced: Sufficient pressure is achieved using air pumps [7].

 

Another innovation in the mid-19th century was the introduction of metal molds. For the first time in 1847, the forms developed by Joseph Magoun replaced the old ones made of wood, which considerably increased their durability.

The first semi-automatic bottle blowing machine was developed in 1859 by the British Alexander Mein and Howard M. Ashley in Pittsburg. But manual work steps were still necessary. [8]

A milestone was the Owens machine introduced by Michael Joseph Owens in 1903 as the first fully automatic glass machine. A vacuum is created in a tube immersed in the melt and the problematic droplet size is precisely dosed. The arm swings back and presses the drop into the mold. When the vacuum is reversed in compressed air, the drop is blown into the metal mold and the workpiece is given its final shape. With this technology it was possible to produce the enormous amount of four bottles per minute at the time. This technique is called the suction-blow process [9].

Despite this achievement, machine-blown bottles remained heavier than hand-blown ones for many years. In order to outperform the glassmakers, the machines had to work much more precisely. This also explains why the various production processes were operated in parallel for a long time.

 

Significant improvements in drop removal have also been implemented. Karl E. Pfeiffer's gob feeder in 1911 no longer allowed the glass gob to be removed from the melt from above, but instead the melt dripped through an opening in the feeder (riser). The more precise dosing of the amount of glass made it possible to produce more uniform bottles.

In 1924 the IS machine was patented by the namesake Ingle and Smith, the first industrial application followed a few years later. This machine, which only really uses the advantages of the drop process, works according to the blow-and-blow process. A drop is fed into a metal mold and pre-blown. The preformed gob is swiveled into a second mold in which the workpiece is blown to finish.

The first applications of the new process followed a few years later. The first machine from 1927 had four stations: A feeder fed a machine and it could produce four bottles in parallel [10]. The principle of the blow-and-blow process is still valid in mass production today.

See also:[11]

Tubular glass

Until the 19th century, glass tubes were also produced (hand-blown) exclusively discontinuously from one batch or one batch of glass. Then in 1912 E. Danner (Libbey Glass Company) developed the first continuous tube drawing process in the USA; In 1918 he received a patent for it.

In order to produce a glass tube, a glass melt flows as a ribbon onto a rotating ceramic hollow cylinder that is inclined downwards at an angle (Danner pipe). After the supply of compressed air via the inside of the pipe, the glass pipe that is forming is pulled off in the direction of the pipe axis. The drawing speed and the pressure of the air supplied determine the pipe dimensions. If the drawing speed is kept constant, an increase in pressure causes larger diameters and smaller wall thicknesses; If, on the other hand, the drawing speed is varied with a constant supply of blown air, tubes with greater wall thicknesses result. Higher pressure creates smaller diameters. After the drawn tube has been deflected horizontally and passed through a roller conveyor to the drawing machine, pieces about 1.5 m long are cut off. With this method, pipe diameters between 2 and 60 mm can be achieved.

In 1929 L. Sanches-Vello worked out a vertical drawing process in France; here the pipe can first be pulled vertically downwards in a temperature-controlled shaft and then deflected horizontally. A conical nozzle mandrel must be set eccentrically to the drawing nozzle in order to avoid uneven wall thicknesses. The resulting pipe therefore initially has different wall thicknesses, which then balance out after being bent.

With the French process, pipe diameters between 1.5 and 70 mm can be produced; however, the throughput is higher than with the Danner process. Furthermore, it is also possible to use glasses with highly volatile components such as borates and lead oxides, since the temperatures at the drawing nozzle are lower than in the Danner muffle.

A newer, modified Vello process ("downward drawing process"), on the other hand, can produce pipes with a maximum diameter of 350 mm and wall thicknesses of 2 to 10 mm. A pipe redirection is not necessary. A drawing speed of 0.3 m / min can be achieved for borosilicate glass (35 mm diameter). [12]

Glass art and handicrafts

Glass fusing

In many glaziers, the glass is processed using a certain technique, glass fusing.
This technique is a glass processing technique that is around 2200 years old. In the last decades the process has been further developed and enriched with new possibilities. Glass fusing is one of the most modern glass processing techniques today. Glass fusing means melting different pieces of glass together.

In glaziers there is usually a warehouse where different colored, small or large glass plates are stored and arranged. Right parts of these glass plates are nipped off with special pliers. The glass artist then designs, for example, a pattern for the frame of a mirror or a bowl. The often irregularly cut glass parts are then placed next to each other according to the design. The gaps are often filled with powdered glass from crushed glass plates. The glass element is then fused in a furnace at 780-850 ° C. These temperatures are not sufficient to liquefy the glass, but only soften it to such an extent that an intimate connection occurs within the material. This firing process takes about 18 to 22 hours, depending on the thickness and diameter of the glass.

In a second step, the resulting plate is shaped again in a glass melting furnace. For this you need different support forms, often made of clay or unglazed ceramic, into which the glass plate can be lowered or on which it can be shaped. The shape should be slightly larger than the glass plate, as glass expands when heated, but contracts again when cooled. The cooled objects can be ground, sandblasted or engraved.

Glass beads

The glass beads became a sought-after commodity and quickly spread across Europe. For centuries, glass beads have been a popular means of payment in the bartering of gold, ivory, silk and spices. The colorful works of art have been coveted objects for collectors for a number of years.

Glass beads from Venice are the most famous and sought-after pearls in the world. Venetian glass artists have influenced bead makers around the world for several centuries. There the glass beads are made over an open flame. It is a very time consuming process as each bead is individually crafted. A glass rod is heated until it melts using a blowtorch and wrapped around a metal rod until the desired bead shape is achieved. Gradually, further glass colors can be melted onto this basic bead and various decorative elements, such as thin glass threads or wafer-thin glass plates (confettis), can be applied. Then the pearl is cooled very slowly and removed from the rod, creating a hole through which the pearl can later be threaded. These pearls are called winding pearls.

Egypt

In the First Egyptian glass art flower (18 to 21 dynasty) there are rod-shaped vessels that go back to models in clay, stone or metal. One knows lotus chalice cups, pomegranate pots, krateriskoi, cabbage pots and cabbage palm pillars, which are regarded as purely Egyptian forms. Especially since Thutmose III. There are also imported vessel shapes from the Mediterranean region (amphoriskoi, lentil bottle, hanging bottle, bilbils and special shapes). The vessels are mostly dark blue-black or white-gray. As decoration you can see thread decorations in zigzag or garland form in yellow, white and light blue as well as twisted threads in a light-dark contrast. All of these vessels are used to store oils, perfumes and other make-up utensils.

In the Second Egyptian art glass flower (Third interim period until Persian rule) the forms are canonized and are limited to Arybaloi, Alabastra, Amphoriskoi and Oinuchoi. Special shapes are very rare, all vessels are decorated with a thread decoration.

In the Third Egyptian Artificial Glass Flower (Hellenism), together with new manufacturing techniques, a completely new world of forms appears. In addition to inlays and pearls, we find multicolored mosaic bowls and the vessels of the "Canossa Group".

Roman Empire

The Romans made slide glasses, mostly bell-shaped, sumptuous drinking vessels that are admired to this day for their artistic quality. One of the most famous Roman glasses is that owned by the British Museum Lykurgos cup[13]