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Glass is a homogeneous amorphous, isotropic, transparent, solid and brittle substance in a metastable state, formed by cooling the melt. It mostly contains siliceous sand, soda, alkali metal oxides, limestone. It is a biologically inactive material.

Glass is transparent (transparent) to visible light (opaque glass also exists). Ordinary glass does not transmit light with a wavelength shorter than 400 nm (ultraviolet light) because it contains impurities, e.g. soda (sodium carbonate).

Glass was discovered around 3000 BC. in Egypt. Initially, the technology did not allow the production of pure glass (admixtures) and it was mainly used for the production of small vessels and ornaments. The vessels were processed by wrapping around a clay core, which broke after the glass product cooled. The glass contained silica, calcium and sodium.

Glass is also found in nature, and is formed from volcanic melt. This glass is called obsidian. Obsidian has long been used to make knives using simple tools. Another form of natural glass are tubes created by lightning striking silica sand.





Glass is a homogeneous, amorphous, rigid, brittle, mostly transparent material with a smooth surface. It is made from the so-called enamel melted in a glass furnace. The material cools quickly and therefore does not have enough time to form a crystal lattice. The resulting solid is amorphous (shapeless). Pure glass is a transparent, relatively strong, wear-resistant, essentially inert and biologically inactive material. It can be molded into a variety of shapes. However, the glass is very fragile and breaks into sharp shards. These properties can be modified by adding compounds (most often metal oxides) to the melt. Glass can also be heat treated, e.g. to tarnish.

Glass is made primarily of silica, which is obtained from quartz (silica sand - also glass sand). Quartz has a melting temperature of around 2,000 °C, therefore, during production, alkaline substances are added, which significantly reduce this temperature, e.g. soda and potassium carbonate, which lowers the melting point to about 1000°C. Since alkalies also reduce the resistance of glass to water, which is undesirable, calcium oxide is also added, which improves this resistance.

The basic raw materials for glass production are – pure silica sand, calcium oxide, sodium carbonate (potassium), aluminum oxide and glass shards (separated waste). These raw materials are used to make a powder mixture called glass stock, which is melted in a glass furnace. Various additives are added to the basic components of the stem, which clean, color or make the glass opaque.

 Quartz glass
Glass made only from pure silica SiO2 (quartz) is called quartz glass. Compared to ordinary glasses, it has some different properties. It does not absorb ultraviolet radiation, has a very high melting point (around 1650 °C), is hard, scratch-resistant, optically pure (does not contain impurities), does not distort the wavelength of the passing light (color error). Therefore, it is used where these properties are required. For example for banks of halogen lamps that work at high temperatures, lamps for ultraviolet light, cover glasses of thermal appliances, watches, etc. Due to the high melting temperature, quartz glass is much more complicated and expensive to manufacture than ordinary glass. Quartz glass can be made so pure that hundreds of kilometers of glass are transparent to the infrared wavelengths of light used in optical fibers. Quartz glass is also used in optics to make lenses and mirrors.

Leaded glass, also lead crystal, has better visual optical properties because the increased refractive index (refraction) causes many more reflections. Such glass is used for the production of artistic glass objects. Boron is added to change the thermal and electrical properties. The addition of barium increases the optical refractive index of the glass. Thorium oxide gives the glass a very high refractive index and is used to make high quality lenses. Larger amounts of iron are used in glass to absorb infrared energy, e.g. for heat-absorbing film projector filters. Cerium is used for glass that absorbs UV wavelengths (biologically harmful radiation).

Metals and metal oxides are added to the enamel during production also to change the color of the glass. Manganese removes the green shade of iron, in higher concentrations it gives an amethyst color. like manganese, selenium is used for decolorizing glass, in higher concentrations it gives a red color. Small concentrations of cobalt (0.025–0.1%) give blue glass. Tin oxide with antimony and arsenic oxides produces an opaque white glass, first used in Venice to make imitation porcelain. Using two to three percent copper oxides produces a turquoise color. Pure metallic copper gives a very dark red opaque glass that is used as a substitute for golden ruby glass. Nickel produces blue, purple or black glass depending on the concentration. The addition of titanium produces a yellow-brown glass. Gold in very small concentrations (around 0.001%) produces a ruby colored glass. Uranium (0.1–2%) is added to give a fluorescent yellow or green color. Silver compounds (mainly silver nitrate) produce a range of colors from orange-red to yellow. The method by which the glass is heated and cooled can also affect the color produced by these compounds. New glass colors and new uses often appear due to newly explored properties.

Enamel processing
Liquid enamel is further processed by blowing, pressing, and casting by hand or by machine. The resulting semi-finished products can be further modified by grinding, polishing, painting, etching...

Blowing is a classic glassmaking technique for manual or machine processing of enamel. The principle is the attachment of viscous enamel to a glass pipe into which air is forced. This will create a bubble at the end of the tube. By simultaneously pushing the air and turning the whistle, the enamel is kept axially centered. Machines are produced in this way, e.g. bottles, glasses, decanters, etc. Hand blowing mainly creates hollow art objects, glasses, decanters, chemical glass (banks, coolers) and so on. These objects do not always have to be hollow. Full subjects can also be processed, such as paperweights, flowers and many items for decorative use.

Enamel can be cast. It is cast into metal (in case of manual processing, also into wooden) molds. The disadvantage is a lower quality surface. Bottles, plates, glasses, glass semi-finished products (pipes, couplings) are cast.

Sheet glass
Glass sheets (sheet glass) are produced by casting into flat molds. There is rolled and floated glass. To achieve an ideally flat and smooth surface / float glass / plate glass, the inside of the mold is made of molten tin. This technique is called float coating, originally from England. The liquid enamel therefore floats in the form on the liquid tin. This glass is called float. It is produced in customer format from 3-19 mm in size 200/225*321 cm and 600x321 cm. Sometimes a metal grid (safety glass) is poured into the plate glass - this is glass with a wire insert, the so-called "wired". This glass is rolled. Such glass does not break into loose shards after breaking, but remains cracked as a whole. It is quite fragile, but it is sufficient as a safety glass. The glass in cars is both toughened and laminated - the front and rear glasses are glued (glass-foil-glass) and the side glasses are toughened. After breaking the glued glass, the shards remain stuck to the foil. Tempered glass breaks into many small circular shards. Bulletproof glass is produced as multi-layered laminated glass. Glass with a thickness of 3-5 mm is used, alternated with a safety film.


Fusing – fusing glass
Fusing is a technique used in the sintering and shaping of glass using high temperatures. Currently, it belongs to common methods of glass processing, such as grinding, pressing, shaping, bending, etc.

Fusing technology has been known since ancient times, as evidenced by archaeological evidence from around 2000 BC. They were the first to use a technique similar to today's fusion of Egyptians and Romans.

With the development of blown glass, fusing recedes into the background. The rediscovery of this technique only happened in the course of the 19th century in Europe. Currently, fusing glass is becoming a popular item in interior decoration and architecture.


Other uses of glass
Semi-finished products are also produced from glass, which are used for further processing. An example is glass fibers, which serve as a semi-finished product for the production of glass fabrics, e.g. ropes, wicks, reinforcing grids, mats, braided fibers, glass wool, etc.

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