Bent Glass

Bent glass is normal glass curved by a special process. Bent or curved glass is a great alternative to the conservative rectangular design of buildings as it is available in a wide range of sizes, allowing the creation of unique and unconventional shapes. Bent glass enhances aesthetics of architectural structures.

Production

Any form of bent glass starts with flat glass and is typically produced in a horizontal mould by slowly heating the glass to approximately 600°C. The heat makes the glass soften sufficiently, transforming flat glass into various shapes of the mould. The glass gradually takes the shape of the mould and is afterwards slowly air cooled to avoid any internal stress. The mould is very important because it alone determines what the glass would look like. The mould determines the quality and the angle of the curve.

Bent glass offers significant advantages over normal glass: the thickness of the glass can be significantly reduced and this obviously reduces the overall weight of the structure and thus its cost. The extra rigidity of bent glass allows for greater freedom in the architectural design, where more space can be covered with glass. This is an especially important advantage when it comes to designing skylights. The lighter the structures and frameworks are, the less material that is required, and lower the cost.

Bent Laminated Glass

Typical applications for bent laminated glass include railing systems, elevator and revolving door enclosures, skylights and overhead glazing, and interior partitions. In addition to minimizing risk of injury from broken glass fragments, bent laminated glass is effective in security areas, reduces sound transmission, blocks potentially harmful ultra-violet light rays, and is available in a range of color tints.

Applications

Bent glass adds a special touch to aesthetic design. Curved glass surfaces can be used as part of the building facade or to make up the whole façade as well as have different applications for external and sites. Some of the external, architectural and internal applications are listed:

External applications

1. Facades
2. Shop fronts
3. Windows
4. Panoramic lifts

Internal applications

1. Showcases
2. Shower doors and enclosures
3. Curtain walls
4. Refrigerator cabinets
5. Elevator glass panels
6. Partitions
Architectural applications

• Domes
• Solariums/Aquariums
• Barrel Vaults
• Revolving doors

Photovoltaic Glass

Photovoltaic glass is a special glass with integrated solar cells that convert solar energy into electricity. This means that the power for an entire building can be produced within the roof and façade areas. The solar cells are embedded between two glass panes and a special resin is filled between the panes, securely wrapping the solar cells on all sides. Each individual cell has two electrical connections, which are linked to other cells in the module, to form a system which generates a direct electrical current.

Need for Photovoltaic Glass

Apart from providing privacy and protection from noise and rain, other features such as thermal insulation and shading are becoming increasingly desirable. All of these functionalities can be obtained simply by installing photovoltaic glass to the shell of a building.

How does it work?

As seen in the science behind PV, a photovoltaic cell is created when a positively charged (P-type) layer of silicon is placed against a negatively charged (N-type) layer of silicon to create a diode and this diode is connected in a circuit via metal conductors on the top and bottom of the silicon sandwich. Though different types of photovoltaics vary in their structure, they generally include the following elements:

1. The cell or multiple cells are the core of the photovoltaic panel.
2. A glass cover is placed over the photovoltaic cell to protect it from the elements while allowing sunlight to pass through to the cell.
3. An additional plastic anti-reflective sheet is often used to enhance the effect of the glass cover and anti-reflective coating of the cell to block reflection.
4. A panel backing (typically plastic) and frame complete the photovoltaic panel, holding all the pieces together and protecting it from damage during installation.
   

Production

The solar cells are embedded between two glass panes, and a special resin fills between the panes, securely wrapping the solar cells on all sides. Each individual cell has two electrical photovoltaic modules (PVs).

A photovoltaic module or photovoltaic panel is a packaged interconnected assembly of photovoltaic cells, also known as solar cells. The photovoltaic module, known more commonly as the solar panel, is then used as a component in a larger photovoltaic system to offer electricity for commercial and residential applications.

Photovoltaic modules enable the active use of solar radiation by turning it into electrical energy; in addition, they can also represent a form of passive solar protection. The most well known PV products are silicon solar cells, available in three types:

1. Monocrystalline:

The monocrystalline solar cells are opaque, blue, or dark grey to black, and they have a high efficiency (14% to 16%). They are expensive because they are made from silicon crystals in a complicated manufacturing process.

2. Poly- or multicrystaffine:

The polycrystalline solar cells are mostly blue or opaque. These are cheaper because they are made from poured silicon blocks, but they have a lower efficiency (14%). Crystalline solar cells are produced as 0.4mm thick discs in sizes from 10 x 10cm to 15 x 15cm. These discs are then put together to form modules and embedded with resin in the cavity in a laminated glass unit. According to composition, the result can be either a transparent, translucent or a non-transparent module.

Light transmission through transparent and translucent modules can be set from 4% to 30% according to the choice of spacing. Special light-scattering and insulating glass elements have been developed to meet both the needs in terms of lighting and insulation as well as the desire to maintain and exploit the corporate image as protected through the façade. In the exterior laminated glass, PV cells have a 5mm gap between them. On the inside, a laminated glass with an opaque interlayer is used.

3. Amorphous:

Amorphous is a non-crystalline solar cells. Amorphous modules are transparent, can be used as window glazing in usual windows, sunspaces, they can be integrated into roofs etc. Transparent modules can be also part of energy efficient glazing, where they are used instead of usual glass.

Optimized exploitation of solar energy can be achieved by combining several thin film layers with different spectral responses. So-called tandem cells have reached up to 12% efficiency under laboratory conditions, slightly higher values seem possible. Further possibilities are offered by triple cells which consist of a succession of three thin film layers Efficiencies of 10% in production quantities are becoming realistic.

Liquid Crystal Glass

Introduction



Liquid crystal glazing is the use of glass that allows you to switch between transparency and translucence at the push of a button. The secret of the transformation between clear glass and translucent glass is found in its ‘Liquid Crystal Sheet’. Liquid crystal glazing comprises laminated glass, with a minimum of two clear or coloured sheets of glass and a liquid crystal film, assembled between at least two plastic interlayers. In the ‘off’ state, the liquid crystals are not aligned, which prevents vision, yet allows light to pass through the glass. When is it switched ‘on’, the liquid crystals align, turning the glass transparent and allowing visibility. The change in transparency takes place within milliseconds.

A piece of glass can adjust the rate of light transmission by changing its transparency or colour. This process is called a ‘chromogenic’ one. There are several types of chromogenics, namely, electrochromic, photochromic, thermochromic and gasochromic etc. The most popular is electrochromic.

Electrochromic:

Electrochromic devices change light transmission properties in response to voltage and thus control the amount of light and heat passing through. In electrochromic windows, the electrochromic material changes its opacity. A burst of electricity is required for changing opacity, but once the change has been effectuated, no electricity is needed for maintaining the particular shade which has been reached.

Darkening occurs from the edges, moving inward, and is a slow process, ranging from several seconds to several minutes depending on window size. Electrochromic glass allows visibility even in the darkened state and thus preserves visible contact with the outside environment. It has been used in small-scale applications such as rearview mirrors.

Electrochromic technology also finds use in indoor applications - for example, for protection of objects under the glass of museum display cases and picture frame glass from the damaging effects of the ultraviolet and visible wavelengths of artificial light.

Two Types:

There are two types of electrochromic: PDLC (polymer dispersed liquid crystal) and SPD (suspension particle device). PDLC is more frequently used.

1. Polymer Dispersed Liquid Crystal Glass (PDLC)

PDLC glass is a light control glass. It can regulate and adjust the light intensity or light transmission through the glass. Sometimes, it is referred to as intelligent glass, magic glass, privacy glass, smart glass or switchable glass.

2. Suspended Particle Device (SPD)

The liquid crystal Suspended Particle Device (SPD) contains molecular particles suspended in a solution between plates of glass. In their natural state, the particles move randomly and collide, blocking the direct passage of light. When energized, the particles align rapidly and the glazing becomes transparent. This type of switchable glazing can block up to about 90 percent of light.
Residential windows with liquid crystal glazing that switches from clear to milky white has been introduced in the U.S. Although the windows do not significantly reduce the amount of light transmission, they provide privacy by reducing transparency. This type of glazing requires a steady current to keep the glass in the clear state.

Applications

Liquid crystal glazing is designed for internal applications, including partitions, display cases and bank screens. Liquid crystal glass is a popular choice for the home, corporate environment, or anyplace where there is a need for privacy or protection. Switchable liquid crystal glass is a state-of-the-art glass that provides complete privacy on demand and is becoming popular with builders, designers, architects and consumers. By eliminating the need for shades, curtains or blinds, the liquid crystal in the glass also protects fine furnishings, carpets and displays from UV damage.

High net worth individuals, government bodies and corporate setups use polymer-dispersed liquid crystal regulating light glass to embellish their homes and offices. Disneyland amusement park also uses this kind of glass. It is even used in upper segment cars like the BMW.

Sandblasted Glass

Glass etching is an age-old old method of imprinting images on glass; and one way to do it is by sandblasting. Sandblasting allows for greater variation through the use of different degrees of coarseness in sand, and also for depth blasting, giving the finished product a rich textured appearance.

Sandblasting process

Sandblasting is essentially the process of blasting the surface of glass with grit which peppers the surface, giving it a milky white appearance.

Sandblasting is a general term used to describe the act of propelling very fine bits of material at high-velocity by steam or air to clean or etch a surface. Synthetic particles or small pieces of coconut shell are sometimes used instead of sand in sandblasting applications.

Sandblasting Glass Etching



The sandblasting glass etching process consists of corroding glass by violently projecting sand upon its surface by means of a current of air or steam. The tube conveying the current of air or steam terminates at a nozzle containing a series of fine holes. The sand, is thrown violently against the glass plate or any other body placed within its range, and thus exerts a corroding action. By varying the quantity of the sand, the volume and velocity of the current, as well as the diameter of the jet, the desired effects are obtained.

Bodies much harder than glass have submitted to the action of sand thrown forcibly in this way against their surface, and have been as rapidly worn away. The portions of the glass which are to remain clear are covered with paper, or with an elastic varnish - these substances being sufficiently exempt from the corroding action of the sand.

Sandblasted glass

Sandblasted glass is produced by spraying sand at high velocities over the surface of the glass. This gives the glass a translucent surface, which is usually rougher than that obtained by etching. During sandblasting, only the areas that are to remain transparent are masked for protection. The depth and degree of the translucency of the sand-blasted finishing vary with the force and type of sand used.

The sandblasting technique is used to obscure visibility through glass, but the glass continues to still transmit light as it is diffused through the surface. Patterns and designs can be created using a mask which resists the abrasive force of the grit from the sandblaster. The mask can be hand cut or computer cut depending on the design.

Sand carving is achieved by blasting away the glass for longer periods to get layers of depth. It's necessary to use thicker pieces of glass for this and the various depths are made by cutting away more of the resist each time. This can sometimes be a long winded process but is desirable for its three-dimensional appearance.

If an image is supplied in a vector format, it can be cut directly using a computer aided cutter. Otherwise, the image in the computer needs to be changed to vector lines the cutter can follow, though this can also be a time consuming process if there is tonality to the image. It is better to supply flat graphic images in this case.

Sandblasters

There are two kinds of sandblasters: “Suction” / “Siphon”" & “Pressure” Blast Systems. Pressure systems are ten times faster & much more effective, but also quite a bit more expensive. There are two basic kinds of sand blasters: Blast Cabinets & Portable Blasters
There is a huge variety of abrasive blast media out there each has its purpose. One you want to stay away from is Silica Sand. Blasting with Silica sand causes Silicosis of the lung. Do Not Ever Use It!

If you are looking to blast hand tools, such as saw blades, wrenches, etc., then sandblast cabinet is better. (A “Suction/Siphon” cabinet would probably be sufficient.)

Sandblast Cabinets must have adequate lighting, a dust collector, and two gloves to place your hands inside to blast within the cabinet. One nice part about blasting inside a cabinet is that all the dust is contained, so no respirator is needed. They are also relatively quiet, and some have abrasive separators which allow you to get the maximum life out of the abrasive blast media & consequently save money.

Application

Dividers, doors and shower surrounds are some of the most popular architectural uses of sandblasted glass. Sand-blasted glass can be used in numerous interior design applications in both residential and commercial settings: doors, shower screens, partitions and interior screens, furniture, etc.

Architectural Uses of Sandblasted Glass

Sandblasting effects on shower doors can create wonderfully frosted looks to compliment the appearance of any bathroom. Typical sandblasted shower surround designs include waves or horizontal lines, but some designs are more ornate such as pictorial sea life scenes.

Sandblasted glass panels on front doors are popular and can really add elegance to the front door of a home. Commercial storefronts and doors may feature sandblasted company logos and business names.

Although glass etching is extremely decorative, sandblasting is not done for aesthetics alone. It can be an attractive and practical solution to reduce the appearance of fingerprints on glass. The frosted appearance and/or different textures sandblasting gives glass can make fingerprints and smudges more difficult to see than if the glass was left as is. Sandblasting glass can also help it repel dirt build-up such as on shopping mall doors and shower enclosures.

Some sandblasted glass room divider panels are more like art pieces than just architectural necessities. For example, some upscale hotels or museum lobbies feature large panels of glass with detailed sandblasted etchings that may include figures or animals. Smaller artistic sandblasted glass panels may be used as architectural accents in homes such as in front halls and kitchen sink back splashes.

Even small amounts of sandblasted glass can add interest to any residential or commercial outdoor or indoor space. Designs for architectural sandblasting are created on computer software programs.

Stencils and sandblasting machines are used to transfer the design onto the glass. To create small pieces of etched glass, it's possible to cover a piece of glass with contact paper and then cut out a design from the paper using a utility knife. Sandblasting equipment can then be used to create a sandblasted effect on the areas not covered by the paper and the contrast between the sandblasted and plain glass is revealed after the remaining paper is peeled off the glass.

Acid-Etched Glass

Acid etching is a process that uses a strong acid to cut into another substance. It is used for both industrial and artistic purposes. For example, etching can be used to prepare flooring like cement for painting or refinishing, while artists use it to create detailed pictures on metal or glass.

Acid-etched glass has a distinctive, uniformly smooth and satin-like appearance. Acid-etched glass admits light while providing softening and vision control.

Origin of Acid-etched glass

During the middle ages, acid glass-etching was somehow clouded with controversy since its acid medium, hydrofluoric acid, caused too much of a health risk to the artisans. In fact the acid was so potent that users were found to have been poisoned even by its mere fumes. Accidents most often happened where a skin contact with the acid dissolved into the tissues, which later resulted in mutilation or loss of the artisan’s fingers. As a result, acid etched glass craftsmanship lacked refinement and thus lost its luster as an art collection.

Now, there are etching tools such as swivel knives, pick knives, adhesive masks aside from the squeegee which makes it possible for an ordinary person to work on acid glass-etching.

Acid-Etching Glass production

Acid etched glass is produced by acid etching one side of float glass. Etched glass is created by cutting a design stencil that is made of an abrasive resistant material, such as vinyl or rubber. The resulting stencil is called a resist. The resist is then secured onto the glass to be etched. A blaster gun, powered by an air compressor, is used to bombard the glass with the abrasive. Every part of the glass that is not covered by the resist will take the frosted effect while the parts protected by the resist will remain clear, thus producing a piece of etched glass.

Etching glass - Hydrofluoric acid

Glass is etched by hydrofluoric acid, or by hydrofluoric acid gas. The gaseous acid has the property of producing a surface which resembles ground glass in its appearance; the liquid acid produces clear etching. Etching glass, therefore, consists of 2 distinct branches. First, the production of a dull image on a clear surface (when the gas is used) and second, the production of a clear image on a surface previously ground or dulled by means of the liquid acid.

The glass plate to be etched is cleaned and gently warmed until hot enough to melt wax. The surface is then covered with an equable layer of white wax, by rubbing the wax over it. When cold, the design is cut out of the wax with a graver. A shallow leaden trough, about the size of the plate (but a trifle smaller) is obtained, into which is placed a small quantity of finely - powdered fluorspar. This must be weighed and then gently sifted over the bottom of the trough. To every 2 parts by weight of fluorspar add 3 of good oil of vitriol. Stir quickly with a wooden stick, and place on the hob or other warm place. Vapour will soon rise.

Now the trough is removed and covered over with the waxed and graved plate, wax side downwards. In a very short time, the acid will have etched the bare portions of the glass. When sufficiently etched, remove the wax by melting. To prepare the liquid acid for clear etching, place 2 parts fluorspar and 3 of sulphuric acid in a leaden retort, the tube of which must dip into a leaden bottle half - filled with water.

Apply heat to the retort as long as the water will absorb the fames generated. If a ground glass be prepared with wax, as above, and a ledge of wax or putty be made round it, on pouring the liquid acid on the plate, clear lines on the dull ground will result; or a "flashed" colored glass may, by the same means, a colorless picture on a colored ground can be done. The sheets of clear glass may themselves be dulled by exposing them, without previously waxing, to the fumes of the acid gas.

Applications

Acid etched glass is perfect for both interior and exterior applications. Architecture and construction, like in houses, restaurants, hotels, commercial buildings, etc. They are found in many residential applications such as home decoration like furniture components. Some of the suggested applications are:

• Interior partitions
• Railings
• Shelves
• Shower and bath enclosures
• Doors and windows
• Glass walls
• Kitchens
• Interior and exterior doors

Etched Glass

Decorative glass of the nineteenth and twentieth centuries was sometimes put through a process of ‘etching’ to produce a frosted pattern. Etched glass is the result of intentional and often artistic carving of the surface of glass to leave a white, frosted finish. This technique is used to create designs on the glass.

Etching refers to the technique of creating art on the surface of glass by applying acidic, caustic, or abrasive substances. Etched glass can be found in a wide variety of decorative contexts, including glass doors and windows, furniture, wine bottles, and serving dishes. The skill of the artisan etching the glass will determine the quality and detail of the resulting piece.

There are three ways to create a piece of etched glass:

1. Sand-blasting
2. Acid-etching
3. Chemical etching

Sandblasting

Sandblasting is the act of shooting an abrasive material, such as sand, at a piece of glass. There are three other types of sandblasting techniques: Carving, shading, and surface etching. A combination of all three techniques can also used.

Acid etching

Acid etching uses an acid resistant material to cover areas of the glass that the artist wants protected. Hydrofluoric acid is then applied to the glass to produce the design.

Chemical etching

Chemical etching is another way to produce etched glass and is normally what is found in glass etching kits. Just as in sandblasting, a stencil is used to protect the glass where the etching effect is not desired. Instead of an abrasive, however, a chemical cream is applied to the glass. It is this etching cream that produces the final frosted effect.

Acid etching can create the same appearance as sandblasted glass. One of the major advantages of acid etching over sand blasting is that it can be done simply and without as many tools. A frosting effect can also be achieved using different strengths of acid etching compounds.

Body-tinted Glass

Body-tinted glass is normal float glass into whose melt colorants are added for tinting and solar-radiation absorption properties. This tinted glass saves energy and reduces heat penetration into buildings and gives a striking visual effect. Coloured glass is an important architectural element for the exterior appearance of façades.

Tinted glass refers to any glass that has been treated with a material such as a film or coating, which reduces its ability to transmit light. Glass can be tinted with various types of coating, which block and/or reflect different amounts and types of light, according to the needs and preferences of the consumer. Glare reduction is another important property of tinted glass. Glare

The production process of body-tinted glass is similar to that of float glass. The only variation is in the colorants mixed at the beginning with the standard raw materials. Body-tinted glass is produced when colorants and iron are introduced during the glass manufacturing process. Different additives may produce differently coloured glasses. Bronze, dark grey and green are the commonly used tints.

The end product does not affect the basic structure of the glass itself, but does enhance its performance in relation to the (solar) electromagnetic spectrum. The colour is homogenous throughout the thickness of the glass. The solar energy transmission, shading coefficient and visible light passing through the tinted glass will vary according to the colour selected.

During the float glass melt process, chemical colorants can be added which tint the colour and increase absorption from the sun. This helps minimize the solar radiation that enters a building, keeping it cool from the inside and protecting furniture from fading. As an example of the colorants used - to create a purple exterior, manganese is added, while pinks and reds can be produced from selenium.

Colorants and colors

Some of the most-used colorants and the colours they produce are listed below:

Iron – Green, brown, blue
Manganese – Purple
Chromium – Green, yellow, pink
Vanadium – Green, blue, grey
Copper – blue, green, red
Cobalt – blue, green, pink
Nickel – yellow, purple
Titanium – purple, brown
Cerium – yellow
Selenium – pink, red
Gold – Red
Cadmium-Sulphide – yellow
Carbon & Sulphur – amber, brown

Double-Glazed with High-Performance Tinted Glass

Tinted Glass is intended for universal application. Either as single or double glazing for a basic level of solar control, and even in furniture, interior design, partitions, etc. It is also the base glass for many high performance comfort glasses.

Doubly-glazed tinted glass reduces solar heat gain to below that of bronze or gray tint but has a visible transmittance closer to clear glass. High-performance or spectrally selective tinted glass products are typically light green or light blue. The tint has no effect on the U-factor but reduces solar heat gain. Doubly glazed tinted glass allows 51 percent of solar heat gain and 69 percent transmission of visible light.

Advantages

• Saves energy, controls solar heat and gives a striking visual effect
• Meets the increasing demands for light in workplaces, creates attractive interiors and gives a feeling of spaciousness
• Offers a practical, stylish alternative to traditional materials when used in screens, partitions and furniture at home or in the office
• Gives designers the freedom to create attractive modern environments that are also economical and easy to maintain
  

Body tinted glass gives the added benefit of making a building look unique and contemporary, creating a lasting impression for business HQs.
Applications

The range of available thicknesses enable glass to be used where superior strength, greater spans, reduced deflection, higher daylight transmission and enhanced noise suppression are required.

Automobiles

One of the most common applications of tinted glass is in automobile windows. Almost all cars come with tinting at the top of the windshield to reduce solar glare when the sun is low in the sky. Apart from this, the windows of several cars are tinted either at the factory or as an aftermarket add-on by the consumer, to provide privacy to the car’s occupants, as also to reduce the build-up of heat in a car while it is parked outdoors.

Dwellings

Another popular use of tinted glass is in windows of homes and commercial buildings. Residential glass tinting is much easier to do than automotive tinting. It can even be done by the homeowner himself, with some practice. Tinted glass in homes serves many practical purposes, such as limiting ultraviolet light transmission through windows, and reducing overall heat gain inside the home by reflecting solar heat energy, thereby saving the homeowner money on air-conditioning.

Commercial Buildings

Tinted glass is also used in commercial buildings. Apart from keeping the interiors cooler, it gives the outside of a building a more uniform, aesthetically pleasing appearance. Depending on the creative use of different colours of tinted glass, the building can also take on a unique and interesting appearance while being insulated from the sun at the same time.

Self Cleaning Glass

Self-cleaning glass is a specific type of glass with a surface which keeps itself free of dirt and grime through photocatalytic decomposition. A nanometer-scale coating of titanium dioxide on the outer surface of the glass introduces two mechanisms which give it the self-cleaning property. Harsh chemicals that are used to clean normal glass are usually washed off into the soil and contaminate it. The use of self cleaning glass eliminates this environmental hazard.

Dual Process

Self cleaning glass cleans itself in two stages. The first stage is called photo-catalysis which is the action of light on the surface of the glass to basically chomp away or eat the dirt on the surface. The next is a process known as hydrophilicity. This basically ensures that any water that falls on the surface forms sheets and washes away dirt uniformly. The glass spreads the water evenly over its surface, without forming droplets.

Working process of the Self Cleaning Glass


Self Cleaning Glass has a coating of titanium dioxide on its outer surface. Titanium dioxide is an inorganic pigment which is widely used in a several products: everything from sunscreen where it reflects away some of the sun’s UV rays through to toothpaste through to the whitener responsible for the white colour in white paint or even in paper.

Titanium dioxide is present as a very thin coating on the outside surface of the glass. It has a thickness of about 25mm. The action of sunlight on the titanium dioxide generates a species known as electrons and holes. These electrons and holes, along with a specific property of titanium dioxide migrate to the surface and start a process known as oxidation of any organic material which is present. Effectively, the titanium dioxide absorbs the UV component of sunlight and causes the degradation and break-down of any organic material, dust or debris which are on the surface of the glass - It converts them into carbon dioxide and water. One of the best features of this is that it works on the bottom of the dirt outwards and so loosens the dirt on the material coating by destroying the contact layer of the dirt and the glass.

Any rain water impacting the surface will form a very smooth sheet which washes down foreign particles uniformly. This happens through the action of sunlight on titanium that produces a surface which is highly hydrophilic, or water-loving. Water loves wetting the surface and the action of sunlight generates hydroxyl species on the surface effectively.

Everything that settles on self cleaning glass is washed down at the same rate, but this property primarily works on surfaces which have some form of slant. If the surface is perfectly horizontal then it would struggle because of a lack of gradient for the water to run off.
Only a small amount of sunlight is required to activate the coating, which ensures that self-cleaning property will function even on cloudy days. A simple rinse with water during dry spells will help keep the surface clean.

Performance

The performance of self-cleaning glass can vary depending on the environment and the location of the glass. The other factors in play are:

1. The type of dirt
2. The amount of dirt
3. Total exposure to light and rain
4. The incline of the installation

Optimum performance is obtained when the glass is installed in a vertical position, and receives maximum exposure to direct sunshine and rain.

Applications

Self cleaning glass is very effective in highly polluted areas. The areas of its application are as follows:
• Glazed facades, exterior shop fronts, display windows, overhead & atria glazing
• Conservatories, balconies, overhead glazing
• Windows & patio doors

Advantages

1. Less frequent cleaning – facade stays cleaner for longer
2. Much easier cleaning - less dirt and grime adheres to the glass
3. Save money - the cost of facade cleaning is reduced
4. Clear vision through the facade - even when it is raining
5. Neutrality and transparency is the same as that of normal glass
6. Less frequent use of detergents – saves the environment.

Bullet Proof Glass

Bullet proof glass or bullet resistant glass refers to any type of glass that is built to stand up against being penetrated by bullets. Although the public uses the term ‘bullet proof glass’, generally within the industry itself it is referred to as bullet-resistant glass, because there is no feasible way to create consumer-level glass that can truly be proof against bullets.

Bullet proof glass is usually constructed using a strong but transparent material such as polycarbonate thermoplastic or by using layers of laminated glass. The desired result is a material with an appearance and light-transmitting behavior of standard glass but offers varying degrees of protection from small arms fire.

The polycarbonate layer, usually consisting of products such as Armormax, Makroclear, Cyrolon, Lexan or Tuffak, is often sandwiched between layers of regular glass. The use of plastic in the laminate provides impact-resistance, such as physical assault with a hammer, an axe, etc. The plastic provides little in the way of bullet-resistance. The glass, which is much harder than plastic, flattens the bullet and thereby prevents penetration. This type of bullet proof glass is usually 70–75 mm (2.8–3.0 in) thick.

Bullet proof glass constructed of laminated glass layers is built from glass sheets bonded together with polyvinyl butyral, polyurethane or ethylene-vinyl acetate. This type of bullet proof glass has been in regular use on combat vehicles since World War II; it is typically about 100–120 mm (3.9–4.7 in) thick and is usually extremely heavy.

Working Principle of the Bullet Resistant Glass

In the bullet proof glass, the Laminate-layers of tough plastic called polycarbonate sandwiched in between the pieces of toughened glass make the glass ten times thicker than the ordinary glass and it is very heavy. If someone fires a bullet at an ordinary piece of glass, the glass can't bend and absorb the energy. So the glass shatters and the bullet carries on through with hardly any loss of momentum. That's why ordinary glass offers no protection against bullets.

But when a bullet strikes bullet proof glass, its energy spreads out sideways through the layers. Because the energy is divided between a number of different pieces of glass and plastic, and spread over a large area, it is quickly absorbed. The bullet slows down so much that it no longer has enough energy to pierce through—or to do much damage if it does so. Although the glass panes do break, the plastic layers stop them flying apart.

Advances in bullet resistant glass have led to the invention of one-way bullet resistant glass, such as used in some bank armored cars. This glass will resist incoming small arms fire striking the outside of the glass, but will allow those on the other side of the glass, such as guards firing from inside the armored car, to fire through the glass at the exterior threat.

One-way Bullet Proof Glass

One-way bullet proof glass is usually made up of two layers, a brittle layer on the outside and a flexible one on the inside. When a bullet is fired from the outside it hits the brittle layer first, shattering an area of it. This shattering absorbs some of the bullet's kinetic energy, and spreads it on a larger area. When the slowed bullet hits the flexible layer, it is stopped. However, when a bullet is fired from the inside, it hits the flexible layer first. The bullet penetrates the flexible layer because its energy is focused on a smaller area; the brittle layer then shatters outward due to the flexing of the inner layer and does not hinder the bullet's progress.

Advancement

The field of bullet proof glass is constantly developing, and there are a number of military projects underway to create lighter-weight, more defensive forms of bullet proof glass. One of the most promising is the use of aluminum oxynitride in the outer layer, in place of a polymer layer.

U.S. military researchers are moving quickly to develop this new class of transparent armour incorporating aluminium oxynitride (Trade name: ALON) as the outside "strike plate" layer. It performs much better than traditional glass/polymer laminates. Aluminium oxynitride "glass" can't defeat threats like the .50 caliber armor piercing rounds using material that is not prohibitively heavy. This more resistant-glass that can be used in military assault vehicles and aircraft.

Applications

Bullet Resistant glasses have a wide range of applications as follows:

• Banks
• Government Buildings
• Convenience Stores
• Churches
• Schools
• Check Cashing Stores
• Liquor Stores
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Glass Types

Flat Glass

Flat glass is the basic material that goes into all types of glass that we see (and see through) every day: All flat glass is made in the form of flat sheets. But some of it, such as that used in automobile windshields, is reheated and sagged (curved) over moulds. It is used to make windscreens and windows for automobiles and transport, and windows and façades for houses and buildings. It is also used, in much smaller quantities, for many other applications like interior fittings and decoration, furniture, "street furniture" (like for bus stops), appliances and electronics, solar energy equipment, and others.

Annealed glass

Annealed glass is the basic flat glass product that is the first result of the float process. It is the common glass that tends to break into large, jagged shards. It is used in some end products -- often in double-glazed windows, for example. It is also the starting material that is turned into more advanced products through further processing such as laminating, toughening, coating, etc.

Laminated Glass

Laminated glass is made of two or more layers of glass with one or more "interlayer’s" of polymeric material bonded between the glass layers. Laminated glass is produced using one of two methods:

1. Poly Vinyl Butyral (PVB) laminated glass is produced using heat and pressure to sandwich a thin layer of PVB between layers of glass. On occasion, other polymers such as Ethyl Vinyl Acetate (EVA) or Polyurethane (PU) are used. This is the most common method.
2. For special applications, Cast in Place (CIP) laminated glass is made by pouring a resin into the space between two sheets of glass that are held parallel and very close to each other.
   

Laminated glass offers many advantages. Safety and security are the best-known of these -- rather than shattering on impact, laminated glass is held together by the interlayer, reducing the safety hazard associated with shattered glass fragments, as well as, to some degree, the security risks associated with easy penetration. But the interlayer also provides a way to apply several other technologies and benefits, such as coloring, sound dampening, resistance to fire, ultraviolet filtering, and other technologies that can be embedded in or with the interlayer.
Laminated glass is used extensively in building and housing products and in the automotive and transport industries.

Alarm Glass

This is a special laminated glass designed and manufactured for security purposes. The inter-layer is embedded with a very thin wire and then “sandwiched” between two or more sheets of glass. The wire forms an electrical circuit which activates an alarm when the glass is forced

Reflective Glass

Reflective Glass is an ordinary float glass with a metallic coating to reduce solar heat. This special metallic coating also produces a mirror effect, preventing the subject from seeing through the glass. It is mainly used in façades. Reflective glasses are mainly manufactured by two different process such as Production Pyrolitic (On-Line) and Vacuum (magnetron) Process (off-line).

Anti-reflective Glass

This is float glass with a specially-designed coating which reflects a very low percentage of light. It offers maximum transparency and optical clarity, allowing optimum viewing through the glass at all times. The clarity of vision makes anti-reflective glass suitable for all applications where glass should be transparent such as exteriors, shop-fronts, commercial frontages and glazing where vision is important, particularly at nighttime. This glass can also be used in interiors for high quality picture framing, display cabinets, interior display windows and dividing screens

Fire-resistant Glass

This can be classified into two categories:

1. Heat-transmitting Glass: Heat-resistant glass is high in silica and usually contains boric oxide. It expands little when heated, so it can withstand great temperature changes without cracking. This contains flames and inflammable gas for a short period of time but does not prevent the transmission of heat to the other side of the glazing. These include wired glass and reinforced laminated glass. This type of glasses is widely used in cookware and other household equipment, and in many types of industrial gear.
   
2. Fire-insulating Glass: This contains flames and inflammable gas for a longer period of time and prevents not only the transmission of flames and smoke, but also of heat to the other side of glazing.

Tempered (toughened) Glass

Toughened glass is made from annealed glass treated with a thermal tempering process. A sheet of annealed glass is heated to above its "annealing point" of 600 °C; its surfaces are then rapidly cooled while the inner portion of the glass remains hotter. The different cooling rates between the surface and the inside of the glass produces different physical properties, resulting in compressive stresses in the surface balanced by tensile stresses in the body of the glass.

These counteracting stresses give toughened glass its increased mechanical resistance to breakage, and are also, when it does break, what cause it to produce regular, small, typically square fragments rather than long, dangerous shards that are far more likely to lead to injuries. Toughened glass also has an increased resistance to breakage as a result of stresses caused by different temperatures within a pane.

This type of glass is mainly intended for glass façades, sliding doors, building entrances, bath and shower enclosures and other purposes that require superior strength and safety.

Low-emission Glass

Glass that has a low-emissivity coating applied to it in order to control heat transfer through windows. Windows manufactured with low-E coatings typically cost about 10–15% more than regular windows, but they reduce energy loss by as much as 30–50%.

A low-E coating is a microscopically thin, virtually invisible, metal or metallic oxide layer deposited directly on the surface of one or more of the panes of glass. The low-E coating reduces the infrared radiation from a warm pane of glass to a cooler pane, thereby lowering the U-factor of the window. Different types of low-E coatings have been designed to allow for high solar gain, moderate solar gain, or low solar gain. A low-E coating can also reduce a window's visible transmittance unless you use one that's spectrally selective.

Window manufacturers apply low-E coatings in either soft or hard coats. Soft low-E coatings degrade when exposed to air and moisture, are easily damaged, and have a limited shelf life. Therefore, manufacturers carefully apply them in insulated multiple-pane windows. Hard low-E coatings, on the other hand, are more durable and can be used in add-on (retrofit) applications. The energy performance of hard-coat, low-E films is slightly poorer than that of soft-coat films.

Self-cleaning glass

Self-cleaning glass is a specific type of glass with a surface which keeps itself free of dirt and grime through natural processes. The first self-cleaning glass was based on a thin film titanium dioxide coating. The glass cleans itself in two stages.
The "photo catalytic" stage of the process breaks down the organic dirt on the glass using ultraviolet light (reflected from the glass)even on overcast days and makes the glass hydrophilic (normally glass is hydrophobic). During the following "hydrophilic" stage rain washes away the dirt, leaving almost no streaks, because hydrophilic glass spreads the water evenly over its surface

Bullet-proof glass

Bullet-proof glass is thick, multilayer laminated glass. This glass can stop even heavy-caliber bullets at close range. Bullet-resisting glass is heavy enough to absorb the energy of the bullet, and the several plastic layers hold the shattered fragments together. Such glass is used in bank teller windows and in windshields for military tanks, aircraft, and special automobiles.

Body-tinted glass

Body-tinted glass is a normal float-clear glass into whose melt colorants are added for tinting and solar-radiation absorption properties. This reduces heat penetration in buildings. Coloured glass is an important architectural element for the exterior appearance of façades. Body-tinted glass is also used in interior decoration.

Production is the same as in float glass production. The only variation is the colorants mixed at the beginning with the standard raw materials. Different additives may produce differently colored glasses.

Sand Blasted Glass

This is produced by spraying sand at high velocities over the surface of the glass. This gives the glass a translucent surface, which is usually rougher than that obtained by etching. During sandblasting, only the areas that are to remain transparent are masked for protection. The depth and degree of the translucency of the sand-blasted finishing vary with the force and type of sand used. Sand-blasted glass can be used in numerous interior design applications in both residential and commercial settings: doors, shower screens, partitions and interior screens, furniture, etc.

Acid-etched Glass

It is produced by acid etching one side of float glass. Acid-etched glass has a distinctive, uniformly smooth and satin-like appearance. Acid-etched glass admits light while providing softening and vision control. It can be used in both residential and commercial settings (doors, shower screens, furniture, wall paneling, etc.).

Wire glass

Wired glass is a product in which a wire mesh has been inserted during production. It has an impact resistance similar to that of normal glass, but in case of breakage, the mesh retains the pieces of glass. This product is traditionally accepted as low-cost fire glass. In the production of wire glass, a steel wire mesh is sandwiched between two separate ribbons of semi-molten glass, and then passed through a pair of metal rollers which squeeze the "sandwich of glass and wire" together.

Stained glass

The term stained glass can refer to the material of colored glass or the craft of working with it. Although traditionally made in flat panels and used as windows, the creations of modern stained glass artists also include three-dimensional structures and sculpture.
"Stained glass" has been applied almost exclusively to the windows of churches, cathedrals, chapels, and other significant buildings.

Fiber glass

Fiberglass, (also called fibreglass and glass fiber), is material made from extremely fine fibers of glass. It is used as a reinforcing agent for many polymer products; the resulting composite material, properly known as fiber-reinforced polymer (FRP) or glass-reinforced plastic (GRP), is called "fiberglass" in popular usage.

Bent Glass

This is a normal glass that is curved with a special process. It can be used for external sites such as facades, shop fronts and panoramic lifts. This glass is also commonly used for internal sites for showcases, shower doors and refrigerator cabinets

Patterned Glass

This glass does not have a perfectly-smooth surface but rather has different patterns impressed on it. The most common method for producing patterned glass is to pass heated glass (usually just after it exits the furnace where it is made) between rollers whose surfaces contain the negative relief of the desired pattern(s). The depth, size and shape of the patterns largely determine the magnitude and direction of reflection. Patterned glass usually transmits only slightly less light than clear glass. It can be used for a variety of applications such as interior design and decorations, furniture, windows and street furniture.

Enamelled Glass

This is tempered or heat-strengthened glass, one face of which is covered, either partially or totally, with mineral pigments. In addition to its decorative function, enameled glass is also a solar ray controller. Enamelled glass is used for glazing and for cladding facades and roofs. It can be assembled into laminated glass or glazed insulation.

Colored structural glass is a heavy plate glass, available in many colors. It is used in buildings as an exterior facing, and for interior walls, partitions, and tabletops.

Soda Glass

Soda Glass is the cheapest & most common glass. It is prepared by fusing soda ash, sand, limestone. It is also called soft glass. It fuses at comparatively low temperatures. The major disadvantage of using this glass is that it is brittle & breaks easily. It cracks when subjected to sudden changes of temperature. Soda glass is used for the manufacture of window glass, glass mirrors, common glassware etc. it is easily attacked by chemicals.

Hard Glass

Hard Glass is obtained by fusing potassium carbonate & limestone. It is used for making hard glass apparatus. It is more resistant to the action of acids.

Lead Crystal Glass

Lead Crystal Glass is made from potassium carbonate, lead oxide & sand. Lead glass has high refractive index. It, therefore, sparkles & is used for making expensive glass ware. The surface of lead glass objects is often cut into decorative patterns to reflect light. Cut glass show extraordinary sparkle.

Pyrex Glass

It is made by fusing a mixture of sand, lime, borax (Na2B4O7.10H2O) & alkali carbonates. It has good chemical laboratory apparatus, ampoules, pharmaceutical containers, etc. In home, it is familiar with oven ware.

Optical Glass

It is specially made so as to be free of strains & defects. It is used for making lenses for spectacles, microscopes, cameras, telescopes & other optical instruments.

Colored Structural Glass

Colored structural glass is a heavy plate glass, available in many colors. It is used in buildings as an exterior facing, and for interior walls, partitions, and tabletops.

Opal glass

Opal glass has small particles in the body of the glass that disperse the light passing through it, making the glass appear milky. The ingredients necessary to produce opal glass include fluorides (chemical compounds containing fluorine). This glass is widely used in lighting fixtures and for tableware.

Foam glass

Foam glass, when it is cut, looks like a black honeycomb. It is filled with many tiny cells of gas. Each cell is surrounded and sealed off from the others by thin walls of glass. Foam glass is so light that it floats on water. It is widely used as a heat insulator in buildings, on steam pipes, and on chemical equipment. Foam glass can be cut into various shapes with a saw.

Photochromic glass

Photochromic glass darkens when exposed to ultraviolet rays and clears up when the rays are removed. Photochromic glass is used for windows, sunglasses, and instrument controls.

Float Glass Production Process

History of float glass

In the earlier days, window glass was made by blowing glass bottles or large glass disks. The bottles were cut into pieces, flattened together and then window panes were cut from the large surface. Most glass for windows up to the early 19th century was made from rondels, while during the 19th century it was done using the bottle method.

Alastair Pilkington has been identified by many sources as the inventor of the float glass process, even though it was first patented in 1848 by Henry Bessemer, an English engineer. Before the development of float glass, larger sheets of plate glass were made by casting a large puddle of glass on an iron surface, and then grinding and polishing both sides for smoothness and clarity - a very expensive process.

Float glass

Float glass is sheet glass made by floating molten glass on a bed of molten tin. This method gives the glass uniform thickness and a very flat surface. Float glass is more commonly known as window glass. Because it is inexpensive and sometimes free, it is often used in the glass fusing process. The molten glass spreads onto the surface of the metal and produces a high quality, consistently level sheet of glass that is later heat polished. The glass has no wave or distortion and is now the standard method for glass production; over 90% of the world production of flat glass is float glass.

Basic float glass process



The phrase “to float” means “to be buoyant”. And this is basically the principle on which the float glass manufacturing process is based. In the float glass process, molten glass is fed onto a float bath of molten tin. This tin bath is 4-8 meters wide and up to 60 meters long. To prevent the tin surface from oxidizing with the atmospheric oxygen, the tin bath is placed under a protective gas atmosphere. This atmosphere must be carefully controlled since its composition is instrumental for the properties of the contact surface between the glass and the tin which, in turn, influence the thickness of the glass sheet.

The glass floats like an endless ribbon on the tin. At the entrance where the glass first makes contact with the tin surface, the temperature of the liquid metal is about 600oC. Tin is the only metal that remains in a liquid state at 600oC.

Immediately after the exit from the float chamber, special rollers take up the glass and feed it into the annealing lehr from which it exits at about 200oC. After cooling to room temperature on an open roller track, it is cut, packed, and stored either for shipment or for further processing into products such as safety glass, reflective glass, self-cleaning glass, mirrors or double glazed or multi-glazed units.

Float glass can be made in thickness between 1.5 to 20mm. There are two techniques to accomplish this. To produce thin float glass, rollers control the width and speed of the glass ribbon. For thick float glass, the glass floats against graphite barriers, so that the ribbon flows out thicker. Thus the desired widths and thicknesses can be achieved.

While each glass plant is different from the other, the float glass production process can be divided into five universal steps:

1. Batching of raw materials:

The main components, namely, soda lime glass, silica sand (73%), calcium oxide (9%), soda (13%) and magnesium (4%), are weighed and mixed into batches to which recycled glass (cullet) is added. The use of ‘cullet’ reduces the consumption of natural gas. The materials are tested and stored for later mixing under computerised control.

2. Melting of raw materials in the furnace:

The batched raw materials pass from a mixing silo to a five-chambered furnace where they become molten at a temperature of approximately 1500°C.

3. Drawing the molten glass onto the tin bath:

The molten glass is "floated" onto a bath of molten tin at a temperature of about 1000°C. It forms a ribbon with a working width of 3210mm which is normally between 3 and 25mm thick. The glass which is highly viscous and the tin which is very fluid do not mix and the contact surface between these two materials is perfectly flat.

4. Cooling of the molten glass in the annealing lehr:

On leaving the bath of molten tin, the glass - now at a temperature of 600°C - has cooled down sufficiently to pass to an annealing chamber called a lehr. The glass is now hard enough to pass over rollers and is annealed, which modifies the internal stresses enabling it to be cut and worked in a predictable way and ensuring flatness of the glass. As both surfaces are fire finished, they need no grinding or polishing.

5. Quality checks, automatic cutting, and storage:

After cooling, the glass undergoes rigorous quality checks and is washed. It is then cut into sheets of sizes of up to 6000mm x 3210mm which are in turn stacked, stored and ready for transport.

Applications

1. Float glass is used for glazing wherever full transparency is required in buildings.
2. It is used as a base material for safety glass, reflective glass and self-cleaning glass, among others.
3. It can be used in precision mechanics, especially where extreme surface flatness is required. Eg., for visual displays.
   

History of Glass Making

What is Glass?

Glass is a type of solid material which is typically brittle and transparent. Glass is commonly used for bottles, glasses, furniture, windows, building facades, and even eyewear. Glass is defined as an inorganic product of fusion which has been cooled through its transition into the solid state without crystallizing. Most glass contains silica as its main component. The term glass was coined in the Roman Empire several centuries ago.

Spark of Glass

Before the human race started to manufacture glass, they had found natural glass in two different forms. When lightning strikes sand, the heat makes sand to fuse into long, slender glass tubes called fulgurites. This kind of glass is commonly called petrified lightning. The tremendous heat from a volcanic eruption also sometimes fuses rocks and sand into a type of glass called obsidian.

Obsidian or Volcanic Glass



In early times, people shaped obsidian into knives, arrowheads, jewellery, and even money. Obsidian was highly prized in prehistory wherever it was found. The glassy material came in a range of colours – right from black and green to bright orange, and was found wherever rhyolite-rich volcanic deposits were found. The shiny beauty, fine texture, and the sharpness of its flaked edges made obsidian a very popular trade item.

It is generally believed that the first manufactured glass was in the form of a glaze on ceramic vessels, around 3000 B.C. The first glass vessels were produced in 1500 B.C. in Egypt and Mesopotamia. The glass industry was extremely successful for the next 300 years, and then saw a decline. It was revived in Mesopotamia in 700 B.C. and in Egypt in 500 B.C. For the next 500 years, Egypt, Syria, and the other countries along the eastern shore of the Mediterranean Sea became glassmaking centers.

At the early stages, glassmaking was a slow and expensive process, and required hard work. Glass blowing and glass pressing were unknown, furnaces were small, clay pots were of poor quality, and the heat was hardly sufficient for melting. But glassmakers eventually learned how to make coloured glass jewellery, cosmetics’ cases, and tiny jugs and jars. People who could afford them—the priests and the ruling classes—considered glass objects as valuable as jewels. Soon merchants learned that wines, honey, and oils could be carried and preserved far better in glass bottles than in wood or clay containers.

Turning point with blowpipes

The blowpipe was invented in 30 B.C., probably along the eastern Mediterranean coast. This invention made glass production easier, faster, and cheaper. As a result, glass became available to the common people for the first time. The long thin metal tube used in the glass blowing process has changed very little since then. In the last century BC, the ancient Romans then began blowing glass inside moulds, greatly increasing the variety of shapes possible for hollow glass items.

Glassblowing

Glassblowing is a glass forming technique that involves inflating the molten glass into a bubble, or parson, with the aid of the blowpipe, or blow tube. A person who blows glass is called a glassblower, glass smith, or gaffer. Free-blowing is a kind of glass blowing technique.

Free-blowing

This glass making technique was used until the late nineteenth century and is still widely used. The process of free-blowing involves the blowing of short puffs of air into a molten portion of glass which is gathered at one end of a blowpipe. This has the effect of forming an elastic skin on the interior of the glass blob that matches the exterior, formed by the removal of heat from the furnace. The glassworker can then quickly inflate the molten glass to a coherent blob and work it into a desired shape.

First Golden Age of Glass: Roman Empire

Glassblowing was greatly encouraged under the Roman rule. Glass manufacture became important in all countries under Roman rule. In fact, the first four centuries of the Christian era can justly be called the First Golden Age of Glass. The glassmakers of this time knew how to make transparent glass, and knew offhand glass blowing, painting, and gilding (application of gold leaf). They knew how to build up layers of glass of different colours and then cut out designs with high precision.

It was the Romans who began to use glass for architectural purposes, with the discovery of clear glass (through the introduction of manganese oxide) in Alexandria around AD 100. Cast glass windows, albeit with poor optical qualities, thus began to appear in the most important buildings in Rome and the most luxurious villas of Herculaneum and Pompeii.

The decline of the Roman Empire and culture slowed progress in the field of glassmaking techniques, particularly through the 5th century. Germanic glassware became less ornate, with craftsmen abandoning or not developing the decorating skills they had acquired.

Early Middle Age

Towards the year AD 1000, a significant change in European glassmaking techniques took place. Given the difficulties in importing raw materials, soda glass was gradually replaced by glass made using the potash obtained from the burning of trees. At this point, glass made in the north of the Alps began to differ from glass made in the Mediterranean area, with Italy, for example, sticking to soda ash as its dominant raw material.

Second Golden Age of Glass

Glass manufacture had developed in Venice by the time of the Crusades (A.D. 1096-1270), and by the 1290's, an elaborate guild system of glassworkers had been set up. Equipment was transferred to the Venetian island of Murano, and the Second Golden Age of Glass began. Venetian glass blowers created some of the most delicate and graceful glass the world had ever seen. They perfected Cristallo glass, a nearly colourless, transparent glass, which could be blown to extreme thinness in almost any shape.

Sheet Glass

The 11th century also saw the development by German glass craftsmen of a technique - then further developed by Venetian craftsmen in the 13th century - for the production of glass sheets.

By blowing a hollow glass sphere and swinging it vertically, gravity would pull the glass into a cylindrical "pod" measuring as much as 3 meters long, with a width of up to 45 cm. While still hot, the ends of the pod were cut off and the resulting cylinder cut lengthways and laid flat.

Glazing remained, however, a great luxury up to the late Middle Ages, with only buildings like royal palaces and churches adorned with glass windows. Stained glass windows reached their peak as the Middle Ages drew to a close.

By the late 1400's and early 1500's, glassmaking had become important in Germany and other northern European countries. It became important in England during the 1500's.

Lead Glass



By 1575, English glassmakers were producing Venetian-style glass. In 1674, an English glassmaker named George Ravenscroft patented a new type of glass in which he had changed the usual ingredients. This glass, called lead glass, contained a large amount of lead oxide. This brilliant glass with a high refractive index was very well suited for deep cutting and engraving.

Plate Pouring Process

In 1688, in France, a new process was developed for the production of plate glass, principally for use in mirrors, whose optical qualities had, until then, left much to be desired. The molten glass was poured onto a special table and rolled out flat. After cooling, the plate glass was ground on large round tables by means of rotating cast iron discs and increasingly fine abrasive sands, and then polished using felt disks. The result of this "plate pouring" process was flat glass with good optical transmission qualities. When coated on one side with a reflective, low melting metal, high-quality mirrors could be produced.

Glass in America

Sandwich Glass, an early American glass was made by the Boston and Sandwich Glass Company, founded by Deming Jarves in 1825. In the early 1800's, the type of glass in greatest demand was window glass. At that time, window glass was called crown glass.

Crown Glass

Other types of sheet glass included crown glass (also known as "bullions"), relatively common across Western Europe. With this technique, a glass ball was blown and then opened outwards on the opposite side to the pipe. Spinning the semi-molten ball then caused it to flatten and increase in size, but only up to a limited diameter. The panes thus created would then be joined with lead strips and pieced together to create windows.

Cylinder Process

By 1825, the cylinder process had replaced the crown method. In this process, molten glass was blown into the shape of a cylinder. After the cylinder cooled, it was sliced down one side. When reheated, it opened up to form a large sheet of thin, clear window glass.

In the 1850's, plate glass was developed for mirrors and other products requiring a high quality of flat glass. This glass was made by casting a large quantity of molten glass onto a round or square plate. After the glass was cooled, it was polished on both sides.

Modern Flat Glass Technology



In the production of flat glass, the first real innovation came in 1905 when a Belgian named Fourcault managed to vertically draw a continuous sheet of glass of a consistent width from the tank. Commercial production of sheet glass using the Fourcault process eventually got under way in 1914.

Around the end of the First World War, another Belgian engineer Emil Bicheroux developed a process whereby the molten glass was poured from a pot directly through two rollers. Like the Fourcault method, this resulted in glass with a more even thickness, and made grinding and polishing easier and more economical.

An off-shoot of evolution in flat glass production was the strengthening of glass by means of lamination (inserting a celluloid material layer between two sheets of glass). The process was invented and developed by the French scientist Edouard Benedictus, who patented his new safety glass under the name "Triplex" in 1910. In America, Colburn developed another method for drawing sheet glass.

The float process developed after the Second World War by Britain's Pilkington Brothers Ltd., and introduced in 1959, combined the brilliant finish of sheet glass with the optical qualities of plate glass. Molten glass, when poured across the surface of a bath of molten tin, spreads and flattens before being drawn horizontally in a continuous ribbon into the annealing lehr. Till today, 90 percent of flat glass is manufactured by this process.