How the glass industry

This article is about the material. For other uses, see ).

Studio glass by Tyler Hopkins, demonstrating many of the essential properties of glass

Glass is an amorphous (non-crystalline) solid material that exhibits a glass transition, which is the reversible transition in amorphous materials (or in amorphous regions within semicrystalline materials) from a hard and relatively brittle state into a molten or rubber-like state. Glasses are typically brittleand can be optically transparent. The most familiar type of glass is soda-lime glass, which is composed of about 75% silicon dioxide (SiO₂), sodium oxide (Na₂O) from soda ash, lime (CaO), and several minor additives. The term glass is often used to refer only to this specific use.

Silicate glass generally has the property of being transparent. Because of this, it has a great many applications. One of its primary uses is as a building material, traditionally as small panes set into window openings in walls, but in the 20th-century often as the major cladding material of many large buildings. Because glass can be formed or moulded into any shape, and also because it is a sterile product, it has been traditionally used for vessels:bowls, vases, bottles, jars and glasses. In its most solid forms it has also been used for paperweights, marbles, and beads. Glass is both reflective and refractive of light, and these qualities can be enhanced by cutting and polishing in order to make optical lenses, prisms and fine glassware. Glass can be coloured by the addition of metallic salts, and can also be painted. These qualities have led to the extensive use of glass in the manufacturing of art objects and in particular, stained glass windows. Although brittle, glass is extremely durable, and many examples of glass fragments exist from early glass-making cultures.

In science, however, the term glass is defined in a broader sense, encompassing every solid that possesses a non-crystalline (i.e. amorphous) structure and exhibits a glass transition when heated towards the liquid state. These sorts of glasses can be made of quite different kinds of materials: metallicalloys, ionic melts, aqueous solutions, molecular liquids, and polymers. For many applications (bottles, eyewear) polymer glasses (acrylic glass,polycarbonate, polyethylene terephthalate) are a lighter alternative to traditional silica glasses.

Silicate glass

Silica (the chemical compound SiO₂) is a common fundamental constituent of glass. In nature, vitrification of quartz occurs when lightning strikes sand, forming hollow, branching rootlike structures called fulgurite.

While fused quartz (primarily composed of SiO₂) is used for some special applications, it is not very common due to its high glass transition temperature of over 1200 °C (2192 °F).^[1] Normally, other substances are added to simplify processing. One is sodium carbonate (Na₂CO₃, "soda"), which lowers the glass transition temperature. However, the soda makes the glass water soluble, which is usually undesirable, so lime (calcium oxide [CaO], generally obtained from limestone), some magnesium oxide (MgO) and aluminium oxide (Al₂O₃) are added to provide for a better chemical durability. The resulting glass contains about 70 to 74% silica by weight and is called a soda-lime glass.^[2] Soda-lime glasses account for about 90% of manufactured glass.

Most common glass contains other ingredients added to change its properties. Lead glass or flint glass is more 'brilliant' because the increased refractive index causes noticeably more specular reflection and increased optical dispersion. Adding barium also increases the refractive index. Thorium oxide gives glass a high refractive index and low dispersion and was formerly used in producing high-quality lenses, but due to its radioactivity has been replaced by lanthanum oxide in modern eyeglasses.^{[citation needed]} Iron can be incorporated into glass to absorb infrared energy, for example in heat absorbing filters for movie projectors, while cerium(IV) oxide can be used for glass that absorbs UV wavelengths.^[3]

The following is a list of the more common types of silicate glasses, and their ingredients, properties, and applications:

1. Fused silica glass, vitreous silica glass: silica (SiO₂). Has very low thermal expansion, is very hard and resists high temperatures (1000–1500 °C). It is also the most resistant against weathering (alkali ions leaching out of the glass, while staining it). It is used for high temperature applications such as furnace tubes, melting crucibles, etc.
2. Soda-lime-silica glass, window glass: silica 72% + sodium oxide (Na₂O) 14.2% + magnesia (MgO) 2.5% + lime (CaO) 10.0% + alumina (Al₂O₃) 0.6%. Is transparent, easily formed and most suitable for window glass. It has a high thermal expansion and poor resistance to heat (500–600 °C). Used for windows, containers, light bulbs, tableware.
3. Sodium borosilicate glass, Pyrex: silica 81% + boric oxide (B₂O₃) 12% + soda (Na₂O) 4.5% + alumina (Al₂O₃) 2.0%. Stands heat expansion much better than window glass. Used for chemical glassware, cooking glass, car head lamps, etc. Borosilicate glasses (e.g. Pyrex) have as main constituents silica and boron oxide. They have fairly low coefficients of thermal expansion (7740 Pyrex CTE is 3.25×10^–6/°C^[4] as compared to about 9×10⁻⁶/°C for a typical soda-lime glass^[5]), making them more dimensionally stable. The lower CTE also makes them less subject to stress caused by thermal expansion, thus less vulnerable to cracking from thermal shock. They are commonly used for reagent bottles, optical components and household cookware.
4. Lead-oxide glass, crystal glass: silica 59% + soda (Na₂O) 2.0% + lead oxide (PbO) 25% + potassium oxide (K₂O) 12% + alumina 0.4% + zinc oxide (ZnO) 1.5%. Has a high refractive index, making the look of glassware more brilliant (crystal glass). It also has a high elasticity, making glassware 'ring'. It is also more workable in the factory, but cannot stand heating very well.
5. Aluminosilicate glass: silica 57% + alumina 16% + boric oxide (B₂O₃) 4.0% + barium oxide (BaO) 6.0% + magnesia 7.0% + lime 10%. Extensively used for fiberglass, used for making glass-reinforced plastics (boats, fishing rods, etc.). Also for halogen bulb glass.
6. Oxide glass: alumina 90% + germanium oxide (GeO₂) 10%. Extremely clear glass, used for fiber-optic wave guides in communication networks. Light loses only 5% of its intensity through 1 km of glass fiber.^[6]

Another common glass ingredient is "cullet" (recycled glass). The recycled glass saves on raw materials and energy; however, impurities in the cullet can lead to product and equipment failure. Fining agents such as sodium sulfate, sodium chloride, or antimony oxide may be added to reduce the number of air bubbles in the glass mixture.^[2] Glass batch calculation is the method by which the correct raw material mixture is determined to achieve the desired glass composition.

Physical properties

Optical properties

Glass is in widespread use largely due to the production of glass compositions that are transparent to visible wavelengths of light. In contrast, polycrystalline materials do not in general transmit visible light.^[7] The individual crystallites may be transparent, but their facets (grain boundaries) reflect or scatter light resulting in diffuse reflection. Glass does not contain the internal subdivisions associated with grain boundaries in polycrystals and hence does not scatter light in the same manner as a polycrystalline material. The surface of a glass is often smooth since during glass formation the molecules of the supercooled liquid are not forced to dispose in rigid crystal geometries and can follow surface tension, which imposes a microscopically smooth surface. These properties, which give glass its clearness, can be retained even if glass is partially light-absorbing—i.e., colored.^[8]

Glass has the ability to refract, reflect, and transmit light following geometrical optics, without scattering it. It is used in the manufacture of lenses and windows. Common glass has a refraction index around 1.5. According to Fresnel equations, the reflectivity of a sheet of glass is about 4% per surface (at normal incidence in air), and the transmissivity of one element (two surfaces) is about 90%. Glass also finds application in optoelectronics—e.g., for light-transmitting optical fibers.

Other properties

In the process of manufacture, silicate glass can be poured, formed, extruded and moulded into forms ranging from flat sheets to highly intricate shapes. The finished product is brittle and will fracture, unless laminated or specially treated, but is extremely durable under most conditions. It erodes very slowly and can withstand the action of water. It is resilient to chemical attack and is an ideal material for the manufacture of containers for foodstuffs and most chemicals.

Contemporary production

Main articles: Glass production, Float glass, and Glazier

Following the glass batch preparation and mixing, the raw materials are transported to the furnace. Soda-lime glass for mass production is melted in gas fired units. Smaller scale furnaces for specialty glasses include electric melters, pot furnaces, and day tanks.^[2] After melting, homogenization and refining (removal of bubbles), the glass is formed. Flat glass for windows and similar applications is formed by the float glass process, developed between 1953 and 1957 by Sir Alastair Pilkington and Kenneth Bickerstaff of the UK's Pilkington Brothers, who created a continuous ribbon of glass using a molten tin bath on which the molten glass flows unhindered under the influence of gravity. The top surface of the glass is subjected to nitrogen under pressure to obtain a polished finish.^[9] Container glass for common bottles and jars is formed by blowing and pressing methods. Further glass forming techniques are summarized in the table Glass forming techniques.

Once the desired form is obtained, glass is usually annealed for the removal of stresses. Surface treatments, coatings or lamination may follow to improve the chemical durability (glass container coatings, glass container internal treatment), strength (toughened glass, bulletproof glass, windshields), or optical properties (insulated glazing, anti-reflective coating)

Color

Main article: Glass coloring and color marking

Color in glass may be obtained by addition of electrically charged ions (or color centers) that are homogeneously distributed, and by precipitation of finely dispersed particles (such as inphotochromic glasses).^[10] Ordinary soda-lime glass appears colorless to the naked eye when it is thin, although iron(II) oxide (FeO) impurities of up to 0.1 wt%^[11] produce a green tint, which can be viewed in thick pieces or with the aid of scientific instruments. Further FeO and Cr₂O₃ additions may be used for the production of green bottles. Sulfur, together with carbon and iron salts, is used to form iron polysulfides and produce amber glass ranging from yellowish to almost black.^[12] A glass melt can also acquire an amber color from a reducing combustion atmosphere.Manganese dioxide can be added in small amounts to remove the green tint given by iron(II) oxide. When used in art glass or studio glass glass is colored using closely guarded recipes that involve specific combinations of metal oxides, melting temperatures and 'cook' times. Most colored glass used in the art market is manufactured in volume by vendors who serve this market although there are some glass makers with the ability to make their own color from raw materials.

History of silicate glass

Main article: History of glass

See also: Architectural glass and Stained glass

The term glass developed in the late Roman Empire. It was in the Roman glassmaking center at Trier, now in modern Germany, that the late-Latin term glesum originated, probably from aGermanic word for a transparent, lustrous substance.^[13]

Roman Cage Cup from the 4th century CE

Naturally occurring glass, especially the volcanic glass obsidian, has been used by many Stone Age societies across the globe for the production of sharp cutting tools and, due to its limited source areas, was extensively traded. But in general, archaeological evidence suggests that the first true glass was made in coastal north Syria, Mesopotamia or Ancient Egypt.^[14] The earliest known glass objects, of the mid third millennium BCE, were beads, perhaps initially created as 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.^[15]

Glass remained a luxury material, and the disasters that overtook Late Bronze Age civilizations seem to have brought glass-making to a halt. Indigenous development of glass technology in South Asia may have begun in 1730 BCE.^[16] In ancient China, though, glassmaking seems to have a late start, compared to ceramics and metal work. In the Roman Empire, glass objects have been recovered across the Roman Empire in domestic, industrial and funerary contexts.

Bohemian flashed and engraved ruby glass (19th-century)

Glass was used extensively during the Middle Ages. Anglo-Saxon glass has been found across England during archaeological excavations of both settlement and cemetery sites. Glass in the Anglo-Saxon period was used in the manufacture of a range of objects including vessels, beads, windows and was also used in jewellery. From the 10th-century onwards, glass was employed in stained glass windows of churches and cathedrals, with famous examples at Chartres Cathedral and the Basilica of Saint Denis. By the 14th-century, architects were designing buildings with walls of stained glass such as Sainte-Chapelle, Paris, (1203-1248)^[17] and the East end of Gloucester Cathedral.^[18] Stained glass had a major revival with Gothic Revival architecture in the 19th-century. With the Renaissance, and a change in architectural style, the use of large stained glass windows became less prevalent. The use of domestic stained glass increased until it was general for every substantial house to have glass windows. These were initially of small panes leaded together, but with the changes in technology, glass could be manufactured relatively cheaply in increasingly larger sheets, leading to larger window panes, and, in the 20th-century, to much larger windows in ordinary domestic and commercial premises.

Studio glass by David Patchen. Multiple colors within a single object increases the difficulty of production, as each color has different chemical and physical properties when molten.

In the 20th-century, new types of glass such as laminated glass, reinforced glass and glass bricks have increased the use of glass as a building material and resulted in new applications of glass. Multi-storey buildings are frequently constructed withcurtain walls made almost entirely of glass. Similarly, laminated glass has been widely applied to vehicles for windscreens. While glass containers have always been used for storage and are valued for their hygienic properties, glass has been utilised increasingly in industry. Optical glass for spectacles has been in use since the late Middle Ages. The production of lenses has become increasingly proficient, aiding astronomers as well as having other application in medicine and science. Glass is also employed as the aperture cover in many solar energy systems.

From the 19th century, there was a revival in many ancient glass-making techniques including Cameo glass, achieved for the first time since the Roman Empire and initially mostly used for pieces in a neo-classical style. The Art Nouveau movement made great use of glass, with René Lalique, Émile Gallé, and Daum of Nancy producing colored vases and similar pieces, often in cameo glass, and also using lustre techniques. Louis Comfort Tiffany in America specialized in stained glass, both secular and religious, and his famous lamps. The early 20th-century saw the large-scale factory production of glass art by firms such as Waterfords and Lalique. From about 1960 onwards there have been an increasing number of small studios hand-producing glass artworks, and glass artists began to class themselves as in effect sculptors working in glass, and their works as part fine arts.

In the 21st century, scientists, observing the properties of ancient stained glass windows, in which suspended nanoparticles prevent UV light from causing chemical reactions that change image colors, are developing photographic techniques that use similar stained glass to capture true color images of Mars for the 2019 ESA Mars Rover mission

Chronology of advances in architectural glass

• 1226 – "Broad Sheet" first produced in Sussex
• 1330 – "Crown Glass" first produced in Rouen, France. "Broad Sheet" also produced. Both were also supplied for export
• 1620 – "Blown Plate" first produced in London. Used for mirrors and coach plates.
• 1678 – "Crown Glass" first produced in London. This process dominated until the 19th century
• 1843 – An early form of "Float Glass" invented by Henry Bessemer, pouring glass onto liquid tin. Expensive and not a commercial success.
• 1888 – "Machine Rolled" glass introduced allowing patterns to be introduced
• 1898 – "Wired Cast" glass invented by Pilkington for use where safety or security was an issue.
• 1959 – "Float Glass" launched in UK. Invented by Sir Alastair Pilkington

Other types of glass

New chemical glass compositions or new treatment techniques can be initially investigated in small-scale laboratory experiments. The raw materials for laboratory-scale glass melts are often different from those used in mass production because the cost factor has a low priority. In the laboratory mostly pure chemicals are used. Care must be taken that the raw materials have not reacted with moisture or other chemicals in the environment (such as alkali or alkaline earth metal oxides and hydroxides, or boron oxide), or that the impurities are quantified (loss on ignition).^[21]Evaporation losses during glass melting should be considered during the selection of the raw materials, e.g., sodium selenite may be preferred over easily evaporating SeO₂. Also, more readily reacting raw materials may be preferred over relatively inert ones, such as Al(OH)₃ over Al₂O₃. Usually, the melts are carried out in platinum crucibles to reduce contamination from the crucible material. Glass homogeneity is achieved by homogenizing the raw materials mixture (glass batch), by stirring the melt, and by crushing and re-melting the first melt. The obtained glass is usuallyannealed to prevent breakage during processing.^[21][22]

In order to make glass from materials with poor glass forming tendencies, novel techniques are used to increase cooling rate, or reduce crystal nucleation triggers. Examples of these techniques include aerodynamic levitation (cooling the melt whilst it floats on a gas stream), splat quenching (pressing the melt between two metal anvils) and roller quenching (pouring the melt through rollers).

Network glasses

Some glasses that do not include silica as a major constituent may have physico-chemical properties useful for their application in fiber optics and other specialized technical applications. These include fluoride glasses, aluminosilicates, phosphate glasses, borate glasses, and chalcogenide glasses.

There are three classes of components for oxide glasses: network formers, intermediates, and modifiers. The network formers (silicon, boron, germanium) form a highly cross-linked network of chemical bonds. The intermediates (titanium, aluminium, zirconium, beryllium, magnesium, zinc) can act as both network formers and modifiers, according to the glass composition. The modifiers (calcium, lead, lithium, sodium, potassium) alter the network structure; they are usually present as ions, compensated by nearby non-bridging oxygen atoms, bound by one covalent bond to the glass network and holding one negative charge to compensate for the positive ion nearby. Some elements can play multiple roles; e.g. lead can act both as a network former (Pb⁴⁺ replacing Si⁴⁺), or as a modifier.

The presence of non-bridging oxygens lowers the relative number of strong bonds in the material and disrupts the network, decreasing the viscosity of the melt and lowering the melting temperature.

The alkali metal ions are small and mobile; their presence in glass allows a degree of electrical conductivity, especially in molten state or at high temperature. Their mobility, however, decreases the chemical resistance of the glass, allowing leaching by water and facilitating corrosion. Alkaline earth ions, with their two positive charges and requirement for two non-bridging oxygen ions to compensate for their charge, are much less mobile themselves and also hinder diffusion of other ions, especially the alkalis. The most common commercial glasses contain both alkali and alkaline earth ions (usually sodium and calcium), for easier processing and satisfying corrosion resistance.^[24] Corrosion resistance of glass can be achieved by dealkalization, removal of the alkali ions from the glass surface by reaction with e.g. sulfur or fluorine compounds. Presence of alkaline metal ions has also detrimental effect to the loss tangent of the glass, and to its electrical resistance; glasses for electronics (sealing, vacuum tubes, lamps...) have to take this in account.

Addition of lead(II) oxide lowers melting point, lowers viscosity of the melt, and increases refractive index. Lead oxide also facilitates solubility of other metal oxides and therefore is used in colored glasses. The viscosity decrease of lead glass melt is very significant (roughly 100 times in comparison with soda glasses); this allows easier removal of bubbles and working at lower temperatures, hence its frequent use as an additive in vitreous enamels and glass solders. The high ionic radius of the Pb²⁺ ion renders it highly immobile in the matrix and hinders the movement of other ions; lead glasses therefore have high electrical resistance, about two orders of magnitude higher than soda-lime glass (10^8.5 vs 10^6.5 Ohm·cm, DC at 250 °C). For more details, see lead glass.^[25]

Addition of fluorine lowers the dielectric constant of glass. Fluorine is highly electronegative and attracts the electrons in the lattice, lowering the polarizability of the material. Such silicon dioxide-fluoride is used in manufacture of integrated circuits as an insulator. High levels of fluorine doping lead to formation of volatile SiF₂O and such glass is then thermally unstable. Stable layers were achieved with dielectric constant down to about 3.5–3.7

Amorphous metals

In the past, small batches of amorphous metals with high surface area configurations (ribbons, wires, films, etc.) have been produced through the implementation of extremely rapid rates of cooling. This was initially termed "splat cooling" by doctoral student W. Klement at Caltech, who showed that cooling rates on the order of millions of degrees per second is sufficient to impede the formation of crystals, and the metallic atoms become "locked into" a glassy state. Amorphous metal wires have been produced by sputtering molten metal onto a spinning metal disk. More recently a number of alloys have been produced in layers with thickness exceeding 1 millimeter. These are known as bulk metallic glasses (BMG). Liquidmetal Technologiessell a number of zirconium-based BMGs. Batches of amorphous steel have also been produced that demonstrate mechanical properties far exceeding those found in conventional steel alloys.^[27][28][29]

In 2004, NIST researchers presented evidence that an isotropic non-crystalline metallic phase (dubbed "q-glass") could be grown from the melt. This phase is the first phase, or "primary phase," to form in the Al-Fe-Si system during rapid cooling. Interestingly, experimental evidence indicates that this phase forms by a first-order transition. Transmission electron microscopy (TEM) images show that the q-glass nucleates from the melt as discrete particles, which grow spherically with a uniform growth rate in all directions. The diffraction pattern shows it to be an isotropic glassy phase. Yet there is a nucleation barrier, which implies an interfacial discontinuity (or internal surface) between the glass and the melt

Electrolytes

Electrolytes or molten salts are mixtures of different ions. In a mixture of three or more ionic species of dissimilar size and shape, crystallization can be so difficult that the liquid can easily be supercooled into a glass. The best studied example is Ca_0.4K_0.6(NO₃)_1.4.

Aqueous solutions

Some aqueous solutions can be supercooled into a glassy state, for instance LiCl:RH₂O in the composition range 4<R<8.

Molecular liquids

A molecular liquid is composed of molecules that do not form a covalent network but interact only through weak van der Waals forces or through transient hydrogen bonds. Many molecular liquids can be supercooled into a glass; some are excellent glass formers that normally do not crystallize.

A widely known example is sugar glass.

Under extremes of pressure and temperature solids may exhibit large structural and physical changes that can lead to polyamorphic phase transitions.^[32] In 2006 Italian scientists created an amorphous phase of carbon dioxide using extreme pressure. The substance was named amorphous carbonia(a-CO₂) and exhibits an atomic structure resembling that of silica

Colloidal glasses

Concentrated colloidal suspensions may exhibit a distinct glass transition as function of particle concentration or density

Glass-ceramics

Glass-ceramic materials share many properties with both non-crystalline glass and crystalline ceramics. They are formed as a glass, and then partially crystallized by heat treatment. For example, the microstructure of whiteware ceramics frequently contains both amorphous and crystalline phases. Crystalline grains are often embedded within a non-crystalline intergranular phase of grain boundaries. When applied to whiteware ceramics, vitreousmeans the material has an extremely low permeability to liquids, often but not always water, when determined by a specified test regime.^[37][38]

The term mainly refers to a mix of lithium and aluminosilicates that yields an array of materials with interesting thermomechanical properties. The most commercially important of these have the distinction of being impervious to thermal shock. Thus, glass-ceramics have become extremely useful for countertop cooking. The negative thermal expansion coefficient (CTE) of the crystalline ceramic phase can be balanced with the positive CTE of the glassy phase. At a certain point (~70% crystalline) the glass-ceramic has a net CTE near zero. This type of glass-ceramic exhibits excellent mechanical properties and can sustain repeated and quick temperature changes up to 1000 °C

Structure

Main article: Structure of liquids and glasses

As in other amorphous solids, the atomic structure of a glass lacks any long-range translational periodicity. However, due to chemical bonding characteristics glasses do possess a high degree of short-range order with respect to local atomic polyhedra.^[39]

The amorphous structure of glassy silica (SiO₂) in two dimensions. No long-range order is present, although there is local ordering with respect to the tetrahedralarrangement of oxygen (O) atoms around the silicon (Si) atoms.

Formation from a supercooled liquid[edit]

Main article: Glass transition

In physics, the standard definition of a glass (or vitreous solid) is a solid formed by rapid melt quenching.^{[40][41][42][43][44]} However, the term glass is often used to describe any amorphous solid that exhibits a glass transition temperature T_g. If the cooling is sufficiently rapid (relative to the characteristic crystallization time) then crystallization is prevented and instead the disordered atomic configuration of the supercooled liquid is frozen into the solid state at T_g. The tendency for a material to form a glass while quenched is called glass forming ability. This ability can be predicted by therigidity theory.^[45] Generally, the structure of a glass exists in a metastable state with respect to its crystalline form, although in certain circumstances, for example in atactic polymers, there is no crystalline analogue of the amorphous phase.^[46]

Some people consider glass to be a liquid due to its lack of a first-order phase transition^[47][48] where certain thermodynamic variables such as volume,entropy and enthalpy are discontinuous through the glass transition range. However, the glass transition may be described as analogous to a second-order phase transition where the intensive thermodynamic variables such as the thermal expansivity and heat capacity are discontinuous.^[49] Despite this, the equilibrium theory of phase transformations does not entirely hold for glass, and hence the glass transition cannot be classed as one of the classical equilibrium phase transformations in solids.^[43][44]

Glass is an amorphous solid. It exhibits an atomic structure close to that observed in the supercooled liquid phase but displays all the mechanical properties of a solid.^[47][50] The notion that glass flows to an appreciable extent over extended periods of time is not supported by empirical research or theoretical analysis (see viscosity of amorphous materials). Laboratory measurements of room temperature glass flow do show a motion consistent with a material viscosity on the order of 10¹⁷–10¹⁸ Pa s.^[51]

Although the atomic structure of glass shares characteristics of the structure in a supercooled liquid, glass tends to behave as a solid below its glass transition temperature.^[52] A supercooled liquid behaves as a liquid, but it is below the freezing point of the material, and in some cases will crystallize almost instantly if a crystal is added as a core. The change in heat capacity at a glass transition and a melting transition of comparable materials are typically of the same order of magnitude, indicating that the change in active degrees of freedom is comparable as well. Both in a glass and in a crystal it is mostly only the vibrational degrees of freedom that remain active, whereas rotational and translational motion is arrested. This helps to explain why both crystalline and non-crystalline solids exhibit rigidity on most experimental time scales.

Behavior of antique glass

The observation that old windows are sometimes found to be thicker at the bottom than at the top is often offered as supporting evidence for the view that glass flows over a timescale of centuries, the assumption being that the glass was once uniform but has flowed to its new shape, which is a property of liquid.^[54] However, this assumption is incorrect; once solidified, glass stops flowing. The reason for the observation is that in the past, when panes of glass were commonly made by glassblowers, the technique used was to spin molten glass so as to create a round, mostly flat and even plate (the crown glass process, described above). This plate was then cut to fit a window. The pieces were not, however, absolutely flat; the edges of the disk became a different thickness as the glass spun. When installed in a window frame, the glass would be placed with the thicker side down both for the sake of stability and to prevent water accumulating in the lead cames at the bottom of the window.^[55] Occasionally such glass has been found thinner side down or thicker on either side of the window's edge.^[56]

Mass production of glass window panes in the early twentieth century caused a similar effect. In glass factories, molten glass was poured onto a large cooling table and allowed to spread. The resulting glass is thicker at the location of the pour, located at the center of the large sheet. These sheets were cut into smaller window panes with nonuniform thickness, typically with the location of the pour centered in one of the panes (known as "bull's-eyes") for decorative effect. Modern glass intended for windows is produced as float glass and is very uniform in thickness.

Several other points can be considered that contradict the "cathedral glass flow" theory:

• Writing in the American Journal of Physics, materials engineer Edgar D. Zanotto states "... the predicted relaxation time for GeO₂ at room temperature is 10³² years. Hence, the relaxation period (characteristic flow time) of cathedral glasses would be even longer."^[57] (10³² years is many times longer than the estimated age of the Universe.)
• If medieval glass has flowed perceptibly, then ancient Roman and Egyptian objects should have flowed proportionately more—but this is not observed. Similarly, prehistoric obsidian blades should have lost their edge; this is not observed either (although obsidian may have a different viscosity from window glass).^[47]
• If glass flows at a rate that allows changes to be seen with the naked eye after centuries, then the effect should be noticeable in antique telescopes. Any slight deformation in the antique telescopic lenses would lead to a dramatic decrease in optical performance, a phenomenon that is not observed.^[47]
• There are many examples of centuries-old glass shelving that has not bent, even though it is under much higher stress from gravitational loads than vertical window glass.^{[citation needed]}

The above does not apply to materials that have a glass transition temperature close to room temperature, such as certain plastics used in daily life like polystyrene and polypropylene.

History of perfume

The word perfume is used today to describe scented mixtures and is derived from the Latin word, "per fumus", meaning through smoke. Perfumery, or the art of making perfumes, began in ancient Egypt but was developed and further refined by the Romans, the Persians and the Arabs. Although perfume and perfumery also existed in East Asia, much of its fragrances are incense based. The basic ingredients and methods of making perfumes are described by Pliny the Elder in his Naturalis Historia.

Mesopotamia

The world's first recorded chemist is a person named Tapputi, a perfume maker who was mentioned in a Cuneiform tablet from the 2nd millennium BC in Mesopotamia

India

Perfume and perfumery also existed in India, much of its fragrances were incense based. The earliest distillation of Attar was mentioned in the Hindu Ayurvedic text Charaka Samhita. The Harshacharita, written in 7th century A.D. in Northern India mentions use of fragrant agarwood oil.

Cyprus

To date, the oldest perfumery was discovered on the island of Cyprus.^[2] Excavations in 2004-5 under the initiative of an Italian archaeological team unearthed evidence of an enormous factory that existed 4,000 years ago during the Bronze Age.^[3] This covered an estimated surface area of over 4,000m² indicating that perfume manufacturing was on an industrial scale.^[4] The news of this discovery was reported extensively through the world press and many artifacts are already on display in Rome.^[5][6] The Bible describes a sacred perfume (Exodus 30:22-33) consisting of liquid myrrh, fragrant cinnamon, fragrant cane, and cassia. Its use was forbidden, except by the priests. The women wore perfume to present their beauty.

Islamic

See also: Alchemy and chemistry in Islam

Islamic cultures contributed significantly in the development of Western perfumery in both perfecting the extraction of fragrances through steam distillation and introducing new, raw ingredients. Both of the raw ingredients and distillation technology significantly influenced Western perfumery and scientific developments, particularly chemistry.

As traders, Islamic cultures such as the Arabs and Persians had wider access to different spices, herbals, and other fragrance material. In addition to trading them, many of these exotic materials were cultivated by the Muslims such that they can be successfully grown outside of their native climates. Two examples of this are jasmine, which is native to South and Southeast Asia, and various citrus, which is thought to have originated in Southeast Asia. Both of these ingredients remain important in modern perfumery.

In Islamic culture, perfume usage has been documented as far back as the 6th century and its usage is considered a religious duty. Muhammad said:

“

The taking of a bath on Friday is compulsory for every male Muslim who has attained the age of puberty and (also) the cleaning of his teeth with Miswaak (type of twig used as a toothbrush), and the using of perfume if it is available. (Recorded in Sahih Bukhari).

”

Such rituals gave incentives to scholars to search and develop a cheaper way to produce incenses and in mass production. Thanks to the hard work of two talented Arabian chemists: Jābir ibn Hayyān (Geber, born 722, Iraq), and Al-Kindi (Alkindus, born 801, Iraq) who established the perfume industry. Jabir developed many techniques, including distillation, evaporation and filtration, which enabled the collection of the odour of plants into a vapour that could be collected in the form of water or oil.^[7]

Al-Kindi, however, was the real founder of perfume industry as he carried out extensive research and experiments in combining various plants and other sources to produce a variety of scent products. He elaborated a vast number of ‘recipes’ for a wide range of perfumes, cosmetics and pharmaceuticals. His work in the laboratory is reported by a witness who said:

“

I received the following description, or recipe, from Abu Yusuf Ya'qub b. Ishaq al-Kindi, and I saw him making it and giving it an addition in my presence.

”

The writer goes on in the same section to speak of the preparation of a perfume called ghaliya, which contained musk, amber and other ingredients; too long to quote here, but which reveals a long list of technical names of drugs and apparatus. Al-Kindi also wrote in the 9th century a book on perfumes which he named ‘Book of the Chemistry of Perfume and Distillations’. It contained more than a hundred recipes for fragrant oils, salves, aromatic waters and substitutes or imitations of costly drugs. The book also described one hundred and seven methods and recipes for perfume-making, and even the perfume making equipment, like the alembic, still bears its Arabic name.^[8]

The Persian Muslim doctor and chemist Avicenna (also known as Ibn Sina) introduced the process of extracting oils from flowers by means of distillation, the procedure most commonly used today. He first experimented with the rose. Until his discovery, liquid perfumes were mixtures of oil and crushed herbs, or petals which made a strong blend. Rose water was more delicate, and immediately became popular. Both of the raw ingredients and distillation technology significantly influenced western perfumery and scientific developments, particularly chemistry.

Eggs and floral perfumes were brought to Europe in the 11th and 12th centuries from Arabia, through trade with the Islamic world and with the returning Crusaders. Those who traded for these were most often also involved in trade for spices and dyestuffs. There are records of the Pepperers Guild of London, going back to 1179; which show them trading with Muslims in spices, perfume ingredients and dyes

Western

Knowledge of something perfumery came to Europe as early as the 14th century due partially to Arabic influences and knowledge. But it was the Hungarians who ultimately introduced the first modern perfume. The first modern perfume, made of scented oils blended in an alcohol solution, was made in 1370 at the command of Queen Elizabeth of Hungary and was known throughoutEurope as Hungary Water. The art of perfumery prospered in Renaissance Italy, and in the 16th century, Italian refinements were taken to France by Catherine de' Medici's personal perfumer,Rene le Florentin. His laboratory was connected with her apartments by a secret passageway, so that no formulas could be stolen en route.

France quickly became the European center of perfume and cosmetic manufacture. Cultivation of flowers for their perfume essence, which had begun in the 14th century, grew into a major industry in the south of France. During the Renaissance period, perfumes were used primarily by royalty and the wealthy to mask body odors resulting from the sanitary practices of the day. Partly due to this patronage, the western perfumery industry was created. Perfume enjoyed huge success during the 17th century. Perfumed gloves became popular in France and in 1656, the guild of glove and perfume-makers was established. Perfumers were also known to create poisons; for instance, a French duchess was murdered when a perfume/poison was rubbed into her gloves and was slowly absorbed into her skin.

Perfume came into its own when Louis XV came to the throne in the 18th century. His court was called "la cour parfumée" (the perfumed court). Madame de Pompadour ordered generous supplies of perfume, and King Louis demanded a different fragrance for his apartment everyday. The court of Louis XIV was even named due to the scents which were applied daily not only to the skin but also to clothing, fans and furniture. Perfume substituted for soap and water. The use of perfume in France grew steadily. By the 18th century, aromatic plants were being grown in the Grasseregion of France to provide the growing perfume industry with raw materials. Even today, France remains the centre of the European perfume design and trade.

After Napoleon came to power, exorbitant expenditures for perfume continued. Two quarts of violet cologne were delivered to him each week, and he is said to have used sixty bottles of double extract of jasmine every month. Josephine had stronger perfume preferences. She was partial to musk, and she used so much that sixty years after her death the scent still lingered in her boudoir.

England

Perfume reached its peak in England during the reigns of Henry VIII and Queen Elizabeth I. All public places were scented during Queen Elizabeth's rule, since she could not tolerate bad smells. It was said that the sharpness of her nose was equaled only by the slyness of her tongue. Ladies of the day took great pride in creating delightful fragrances and they displayed their skill in mixing scents.

As with industry and the arts, perfume was to undergo profound change in the 19th century. Changing tastes and the development of modern chemistry laid the foundations of perfumery as we know it today. Alchemy gave way to chemistry and new fragrances were created. The industrial revolution had in no way diminished the taste for perfume, there was even a fragrance called "Parfum à la Guillotine". Under the post-revolutionary government, people once again dared to express a penchant for luxury goods, including perfume. A profusion of vanity boxes containing perfumes appeared in the 19th century.

Americas

In early America, the first scents were colognes and scented water by French explorers in New France. Florida water, an uncomplicated mixture of eau de cologne with a dash of oil of cloves, cassia, and lemongrass, was popular

A full search for the paper industry .. how the paper industry

Material in the form of thin pages made ​​cellulosic fiber weave for vegetables . The material used in these pages of writing and printing , packaging and in the fulfillment of many of purposes , ranging from filtering sediment from solution and industry specific types of building materials.
In the civilization of the twentieth century , it has become an essential element of the paper and became the development of technology for the production responsible for the rapid increase of education and high levels of education among people across the world .
History of the paper industry
Invention of paper back to the third millennium BC (about 2700 BC. AD ) has invented the ancient Egyptians good material for writing , with easy access to this article invaluable in handy , a papyrus . That was one of the greatest inventions in the history of mankind , and before that was the writing ( which appeared in the fourth millennium ) limited to stone or mud flaps and used by the Sumerians , preferring to write on it and found closer to trading , and Acer in the cost of cut stone , the boards made ​​up of silt pure soft , and pour into molds with canonical forms , and they come out the painting on the flat -sided disc , or in the form of a quarter circle flat surface convex back, or in the form of a rectangle . Painting may be in the form of the cone , and leave unchanged , after writing or dried in the heat of normal so gaining appropriate hardness .
The rectangular panels are more common , and were burned in ovens , and kept in the covers of mud after tossing them a little powder dry to prevent silt possess an adhesion , then this breaks cover before reading his portrait of the Interior.
The Egyptians then making paper from papyrus stalks , and resolving place books stone and clay . The papyrus cheaper price and Acer as it was growing in abundance in the swamps of the Delta . The paper pulp to make the cut longitudinal strips are placed in opposing two or three on top of each and then wetted with water and press . It was made ​​as pages separate , and then plastered these pages one at the bottom of the other , and thus might work tapes of different lengths with long texts . The width strips of papyrus has ranged from three feet to 18 feet . The longest known papyrus is Papyrus Harris reached a length of 133 feet and display (16) feet . I have been using papyrus in writing in AD uttered the Mediterranean until the atheist century AD .
The paper is now known , its history goes back to the second century AD . In 105 AD, making Chinese Tse any color paper from the bark of trees, and fish nets . Then come the Chinese to make paper from pulp to the door of the trees disappeared, this place is expensive silk , and the heavy weight of the jungle , who disguised by the Chinese for a long time . After the Chinese developed this material workmanship using fishplates of glue or gelatin mixed with a starchy paste prevailed by fiber paper and make a quick absorption of the ink .
But Chinese paper was limited and did not spread Iva experience in the ancient world or the mediator until the eighth century AD , when the Arabs knew the secrets of the Chinese paper industry after opening Samarkand in 93 AH / 712 AD . And established the first paper mill in Baghdad in 178 AH / 794 AD . And founded al-Fadl ibn Yahya in the era of Harun al-Rashid . Then spread the paper industry by leaps and bounds in all parts of the Islamic world , entered Syria, Egypt , North Africa and Spain , and people were writing until the time of slavery and Alasp and Allkhav , then ordered Harun al-Rashid , after a lot of paper , not people write only in Alkagd .
And developed industry Alkagd Muslims and Islamic factories produced excellent types of it. Among the most famous methods of industry Alkagd in Islamic eras mentioned in the book ' Mayor of the book and several with Kernels ' and it mentions the author of Prince goats bin Badesi way industry Alkagd of material hemp and white way : ' to soak hemp and wander until softened and then soaked in water, lime and rubbed by hand and dried reiterates this process three days and replace the water every time until it becomes white and then cut Palmqrad and soaked with water until relieved lime and then it beats in a mortar , a soprano so as not to keep the contract and then analyzes in the water and it becomes like silk and pour into molds according to the size you want and be a paper cut open strings is attributable to cannabis and hits a strong and boiled in the form of large water and stir on both sides, strong and boiled in the form of large water and stir on both sides, so be Tgena then poured into a mold and stir on a board and pasted on the wall to dry and fall Wei Akhz his smooth delicate and starch in cold water and boil until boiling and pour the flour and stir until Fataly amuse him paper and then damage the paper on a reed to dry from the duplex and then sprinkle with water and dried and polished ' .
During the ten consecutive centuries , until the date of the invention of the first paper machine in the eighteenth century did not change the basic processes used in the paper industry. The raw material was placed in a large basin then Tsahn Bmedkh or sledgehammer to separate the fibers . Then this article is washed with running water to get rid of the dirt , and after separation of the fiber without reservation change the water in the basin. At this stage , the liquid material is ready for the actual papermaking process .
The main machine in the paper industry is the template. This template is placed inside a wooden frame , a movable frame low around its edge . The maker of paper and dip the mold frame in the basin that contains a liquid material , and when they go out of the basin , the mold surface is covered with a thin layer of a mixture of fiber and water. The machine is then rocked back and forth and side to side . This process helps to distribute the mixture evenly over the surface of the mold and make the individual fibers are interwoven with other fibers near them, which makes the paper strong chick . During that run a large part of the water in the mixture over the network in the mold. Then leave the machine and chick wet paper some time until the paper together enough so that they can get rid of the wooden frame around the existing template.
And after removing the wooden frame of the mold , the mold is placed in a position inverted and placed the chick paper on the so-called non-woven homespun pad , then put the pad on the other chick paper and the process is repeated .
After laying pads between the number of chicks paper , placed in a pile all piston and subjected to a pressure of up to 100 tons degree or more where they are getting rid of most of the remaining water in the paper. Then separated from the chicks paper felts and overstock and press . And repeat the process pressure pile of paper several times and each time the pile placed in a different format where the chicks single paper in different modes for the other chicks . This process is called alternately repeated and leads to improve the surface of the leaves that have been completed manufactured . The last stage in the paper industry is the drying stage , where the paper attached in groups of four or five chicks on the ropes in a special drying room until the moisture evaporates completely in it .
For the paper , which uses the ink for the purposes of writing or in print , it requires additional treatment after drying , because without this treatment , will be absorbed by the paper and ink lines appear distorted. Include the treatment process to cover the paper with a layer of glue through Gmesh in a solution of animal glue and then drying the paper they are subjected to this process , and the completion of the paper by pressing the chicks between the metal sheets of paper or cardboard smooth . And determines the strength of the pressure feel of the paper. And pressing the leaves with coarse texture lightly to a relatively short period , while pressing the leaves with a soft texture severe pressure for a relatively longer period .
We have many types of paper in parts of the Islamic state , there was a Ettalhi , and Alnouha , and al-Jaafari , and the Pharaonic , and Tahiri , relative to the names of corrupt officials . This led to facilitate the production of books in a big way . In less than a century , Muslims produced hundreds of thousands of copies of the books , which was decorated with hundreds of public and private libraries all over the world from China in the east to the west of Andalusia .
Enter the Muslims of Andalusia and paper to Europe , and the Europeans at the time they write the Terrapins from the skins of animals , but the monks are accustomed to Knit literature greats Greece Blog slavery to write instead of religious sermons , which led to the loss of much of the heritage of Greece, scientific and cultural .
Then spread craft paper industry in Europe , Vonci the first paper mill in Spain around the year 544 AH / 1150 AD , then deteriorated this industry in Spain , and moved to Italy , and established the first factory for this purpose in the city Verriano year 674 AH / 1276 AD , and set up another factory in Padua in 833 AH / 1340 AD , then the other factories in many Trever , Florence, Bologna , Parma , Milan and Venice . The first paper mill was established in Germany was in the city of Mainz in 719 AH / 1320 AD , followed by another factory in Nuremberg in 792 AH / 1390 AD , while England have delayed the paper industry where for the rest of the European countries for nearly a hundred years was the construction of the first plant where the paper in 1495 AD . During the fifteenth century solution to replace paper skin parchments in writing in Europe . While the paper industry to have entered the United States in the late seventeenth century where he established the first factory in America in 1690 .
And has resulted in increased use of paper in the seventeenth and eighteenth centuries to a shortage in the bark of the wood raw material , which was sufficient only known European paper makers . At the same time , attempts were made to reduce the cost of paper through the invention of the machine replace the hand- molding process used in the paper industry. Has manufactured the first machine in the process of its 1203 / 1789 was invented by French inventor Nicolas Louis Robert . The development of this machine brothers Robert and Henry Fordgnier Ossell Fordgnier year 1217 AH / 1803 AD . It also solved the problem of the paper industry from cheap raw materials through the manufacturing process to reach a pulp around the year 1840 , has also been reached chemically pulp production processes then about ten years .
And currently makes more than 95% of paper from wood cellulose . Wood pulp is used only in the manufacture of cheap types of paper , such as that used in newsprint , but the species is used where the finest chemically treated wood pulp and a mixture of pulp and bark fibers . . The best types of paper - such as those used in writing - those made of bark fiber only .
Papermaking machine
When the paper industry automatically cleans the bark user using the machine in order to get rid of dust or ash and exotic materials . After the cleaning process , the bark is placed in the kettle where a large circular boil bark and lime under pressure steam for up to several hours . And lime combine with fat and other exotic materials in the soap bark to be insoluble , and can get rid of this soap later , as this reduces any lime colored pigment present in the vehicle color . Then turns to bark machine called a Hollander, a basin is divided longitudinally so that they form a continuum around the tub . In one half of the basin , there is a horizontal cylinder carrying a series of knives that spin rapidly near the base plate , a curved knives other provider . And passing the mixture consisting of bark and water between the cylinder and the baseboard and turns to bark fibers . In the other half of the basin , there is a hollow cylinder wash -coated thin is a network organization in a certain way so that sucks water from the basin , leaving behind her bark and fiber . During the flow of a mixture of water and bark about Alholander , is to get rid of dirt and soaked bark gradually until completely disintegrates into individual fibers . After that is inserted in the machine wet bark Hollander subset in order to separate the fibers again. At this point , add the coloring materials and glue Kasamg or type of resin and filler material , such as sulphate of lime or pure clay , so as to increase the weight and size of the paper

Recycling paper is a series of processes that convert waste paper into new materials usable again. The lack of basic materials and human need has generated his desire to invent ways to cover the shortfall or downgraded. Vhajth to rubber, plastic and paper led him to the idea of ​​recycling until the economy and good use of these materials , minimizing waste any McCabe preservation of the environment .
This idea began during World War I and II , and this is what the legacy of pollution , and the large number of scattered waste , where the waste collected for re-use , and with the passage of time has become a process of re- industrialization of the most important methods used in the management of solid waste for their environmental benefits . The programs and campaigns carried out by the NGOs interested in the environment played a major role in the expansion of the public thought the issue of recycling because of its great importance has found great reception among students in schools , and even housewives and members of environmental associations .
Was considered remanufacturing direct basic form before the nineties , but with the beginning of the nineties began to focus on re- industrialization indirect , and this improves manufacturing waste to produce other materials based on the same raw material , such as recycled paper and cardboard, plastic, metal , especially aluminum and others.

Paper recycling process

Main article: deinking

The process of paper recycling involves mixing used paper with water and chemicals to break it down. It is then chopped up and heated, which breaks it down further into strands of cellulose, a type of organic plant material; this resulting mixture is called pulp, or slurry. It is strained through screens, which remove any glue or plastic that may still be in the mixture then cleaned, de-inked, bleached, and mixed with water. Then it can be made into new recycled paper.^[2The same fibers can be recycled about seven times, but they get shorter every time and eventually are strained out.^[3]

Rationale for recycling

Industrialized paper making has an effect on the environment both upstream (where raw materials are acquired and processed) and downstream (waste-disposal impacts).^]

Today, 90% of paper pulp is created from wood ( in most modern mills only 9-16% of pulp is made from pulp logs the rest from waste wood that was traditionally burnt). Paper production accounts for about 35% of felled trees,^[5] and represents 1.2% of the world's total economic output.^[6] Recycling one ton of newsprint saves about 1 ton of wood while recycling 1 ton of printing or copier paper saves slightly more than 2 tons of wood.^[7] This is because kraft pulping requires twice as much wood since it removes lignin to produce higher quality fibres than mechanical pulping processes. Relating tons of paper recycled to the number of trees not cut is meaningless, since tree size varies tremendously and is the major factor in how much paper can be made from how many trees.^[8] Trees raised specifically for pulp production account for 16% of world pulp production, old growth forests 9% and second- and third- and more generation forests account for the balance.^[5] Most pulp mill operators practice reforestation to ensure a continuing supply of trees.^{[citation needed]} The Programme for the Endorsement of Forest Certification (PEFC) and the Forest Stewardship Council (FSC) certify paper made from trees harvested according to guidelines meant to ensure good forestry practices.^[9] It has been estimated that recycling half the world’s paper would avoid the harvesting of 20 million acres (81,000 km²) of forestland.^]

Energy

Energy consumption is reduced by recycling,^] although there is debate concerning the actual energy savings realized. The Energy Information Administration claims a 40% reduction in energy when paper is recycled versus paper made with unrecycled pulp,^] while the Bureau of International Recycling (BIR) claims a 64% reduction.³Some calculations show that recycling one ton of newspaper saves about 4,000 kWh (14 GJ) of electricity, although this may be too high (see comments below on unrecycled pulp) ( recycling paper also produces no free energy in the way of process steam or recovery steam thus making it more expensive to recycle paper than to make new paper^{[citation needed]}). This is enough electricity to power a 3-bedroom European house for an entire year, or enough energy to heat and air-condition the average North American home for almost six months.^] Recycling paper to make pulp actually consumes more fossil fuels than making new pulp via the kraft process; these mills generate most of their energy from burning waste wood (bark, roots, sawmill waste) and byproduct lignin (black liquor).^] Pulp mills producing new mechanical pulp use large amounts of energy; a very rough estimate of the electrical energy needed is 10 gigajoules per tonne of pulp (2500 kW·h per short ton).^]

Landfill use

About 35% of municipal solid waste (before recycling) by weight is paper and paper products.^]

Water and air pollution

The United States Environmental Protection Agency (EPA) has found that recycling causes 35% less water pollution and 74% less air pollution than making virgin paper.^] Pulp mills can be sources of both air and water pollution, especially if they are producing bleached pulp. Modern mills produce considerably less pollution than those of a few decades ago. Recycling paper decreases the demand for virgin pulp, thus reducing the overall amount of air and water pollution associated with paper manufacture. Recycled pulp can be bleached with the same chemicals used to bleach virgin pulp, but hydrogen peroxide and sodium hydrosulfite are the most common bleaching agents. Recycled pulp, or paper made from it, is known as PCF (process chlorine free) if no chlorine-containing compounds were used in the recycling process.^] However, recycling mills may have polluting by-products like sludge. De-inking at Cross Pointe's Miami, Ohio mill results in sludge weighing 22% of the weight of wastepaper recycled.

Recycling facts and figures

n the mid-19th century, there was an increased demand for books and writing material. Up to that time, paper manufacturers had used discarded linen rags for paper, but supply could not keep up with the increased demand. Books were bought at auctions for the purpose of recycling fiber content into new paper, at least in the United Kingdom, by the beginning of the 19th century.

Internationally, about half of all recovered paper comes from converting losses (pre-consumer recycling), such as shavings and unsold periodicals; approximately one third comes from household or post-consumer waste.

Some statistics on paper consumption:

• The average per capita paper use worldwide was 110 pounds (50 kg).
• It is estimated that 95% of business information is still stored on paper.
• Recycling 1 short ton (0.91 t) of paper saves 17 mature trees, 7 thousand US gallons (26 m³) of water, 3 cubic yards (2.3 m³) of landfill space, 2 barrels of oil (84 US gal or 320 l), and 4,100 kilowatt-hours (15 GJ) of electricity – enough energy to power the average American home for six months.
• Although paper is traditionally identified with reading and writing, communications has now been replaced by packaging as the single largest category of paper use at 41% of all paper used.
• 115 billion sheets of paper are used annually for personal computers.^[27] The average web user prints 28 pages daily.
• Most corrugated fiberboard boxes have over 25% recycled fibers^{[citation needed]}. Some are 100% recycled fiber.

Paper recycling by region

European Union

Paper recovery in Europe has a long history and has grown into a mature organization. In 2004 the paper recycling rate in Europe was 54.6% or 45.5 million short tons (41.3 Mt).^[29] The recycling rate in Europe reached 64.5% in 2007, leaving the industry on track to meeting its voluntary target of 66% by 2010.

Japan

Municipal collections of paper for recycling are in place. However, according to the Yomiuri Shimbun, in 2008, eight paper manufacturers in Japan have admitted to intentionally mislabeling recycled paper products, exaggerating the amount of recycled paper used

United States

Recycling has long been practiced in the United States. The history of paper recycling has several dates of importance:

• 1690: The first paper mill to use recycled linen was established by the Rittenhouse family.^[31]
• 1896: The first major recycling center was started by the Benedetto family in New York City, where they collected rags, newspaper, and trash with a pushcart.
• 1993: The first year when more paper was recycled than was buried in landfills.^]

Today, over half of all paper used in the United States is collected and recycled.^[33] Paper products are still the largest component of municipal solid waste, making up more than 40% of the composition of landfills.^[34][35] In 2006, a record 53.4% of the paper used in the US (or 53.5 million tons) was recovered for recycling.^[36] This is up from a 1990 recovery rate of 33.5%.^] The US paper industry set a goal of recovering 55 percent of all paper used in the US by 2012. Paper products used by the packaging industry were responsible for about 77% of packaging materials recycled, with more than 24 million pounds recovered in 2005.^]

By 1998, some 9,000 curbside recycling programs and 12,000 recyclable drop-off centers existed nationwide. As of 1999, 480 materials recovery facilities had been established to process the collected materials.^]

In 2008, the global financial crisis caused the price of old newspapers to drop in the U.S. from $130 to $40 per short ton ($140/t to $45/t) in October.^]

Mexico

In Mexico, recycled paper, rather than wood pulp, is the principal feedstock in papermills accounting for about 75% of raw materials.^]