HOW IS PLATE GLASS MADE?


Plate glass is thick, good quality glass made in huge sheets for shop windows. It’s very smooth surface is made by floating the molten glass onto a bath of molten tin. Tin melts at a lower temperature than glass, so the glass begins to set on the tin and is then passed over rollers as it finishes cooling. The larger the bath of molten tin the larger the glass that can be made.



Plate glass, flat glass or sheet glass is a type of glass, initially produced in plane form, commonly used for windows, glass doors, transparent walls, and windscreens. For modern architectural and automotive applications, the flat glass is sometimes bent after production of the plane sheet. Flat glass stands in contrast to container glass (used for bottles, jars, cups) and glass fiber (used for thermal insulation, in fiberglass composites, and optical communication).



Flat glass has a higher magnesium oxide and sodium oxide content than container glass, and lower silica, calcium oxide, and aluminum oxide content. (From the lower soluble oxide content comes the better chemical durability of container glass against water, which is required especially for storage of beverages and food). Most flat glass is soda-lime glass, produced by the float glass process (1950s). Other processes for making flat glass include:



Scratches can occur on sheet glass from accidental causes. In glass trade terminology these include “block reek” produced in polishing, “runner-cut” or “over/under grind” caused by edge grinding, or a “sleek” or hairline scratch, as well as “crush” or “rub” on the surface.



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WHAT IS GLASS MADE OF?


Glass is an extraordinarily useful material. The substances from which it is made are easy to find and very cheap. Glass is mainly melted, cooled sand, but other ingredients are added, such as sodium carbonate (soda ash) and limestone. Although it appears solid to us, glass is in fact a liquid, flowing incredibly slowly. When windows that are hundreds of years old are measured, they are found to be slightly thicker at the bottom than at the top, as the glass very gradually flows downwards.



In a commercial glass plant, sand is mixed with waste glass (from recycling collections), soda ash (sodium carbonate), and limestone (calcium carbonate) and heated in a furnace. The soda reduces the sand's melting point, which helps to save energy during manufacture, but it has an unfortunate drawback: it produces a kind of glass that would dissolve in water! The limestone is added to stop that happening. The end-product is called soda-lime-silica glass. It's the ordinary glass we can see all around us.



Once the sand is melted, it is either poured into molds to make bottles, glasses, and other containers, or "floated" (poured on top of a big vat of molten tin metal) to make perfectly flat sheets of glass for windows. Unusual glass containers are still sometimes made by "blowing" them. A "gob" (lump) of molten glass is wrapped around an open pipe, which is slowly rotated. Air is blown through the pipe's open end, causing the glass to blow up like a balloon. With skillful blowing and turning, all kinds of amazing shapes can be made.



Glass makers use a slightly different process depending on the type of glass they want to make. Usually, other chemicals are added to change the appearance or properties of the finished glass. For example, iron and chromium-based chemicals are added to the molten sand to make green-tinted glass. Oven-proof borosilicate glass (widely sold under the trademark PYREX®) is made by adding boron oxide to the molten mixture. Adding lead oxide makes a fine crystal glass that can be cut more easily; highly prized cut lead crystal sparkles with color as it refracts (bends) the light passing through it. Some special types of glass are made by a different manufacturing process. Bulletproof glass is made from a sandwich or laminate of multiple layers of glass and plastic bonded together. Toughened glass used in car windshields is made by cooling molten glass very quickly to make it much harder. Stained (colored) glass is made by adding metallic compounds to glass while it is molten; different metals give the separate segments of glass their different colors.



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What is safety glass?


            Safety glass is glass that has been strengthened. There are two kinds of this protective glass-laminated and toughened-and both were discovered by accident.



             In the early 1900s EdouardBenedictus, a French chemist knocked a glass flask on to the floor. Although the glass starred and cracked, it did not break. After examining the flask he realized that a coating of dried celluloid on the inside had held the fragments together.



             Some years later, when injuries from broken car windscreens increased, Benedictus recalled this incident. Using glass sheets and celluloid bonded together in an old letter press, he produced the world’s first sheet of laminated, or layered, glass. Since then the clarity of the glass has been improved to equal that of ordinary glass. But it will withstand the impact of a half-pound steel ball dropped from a height of 16 feet. Toughened glass was developed later, although in the 17th century, Prince Rupert, nephew of king Charles I of England, discovered that molten glass was turned into immensely strong pear-shaped drops when tipped into cold water. Prince Ruport’s drops, as they are called, can be hammered on an anvil without breaking, but if the tail of the drop is broken they crumble into dust.



             In 1874 a French scientist, de la Bastie, heated small sheets of glass and then quenched them in oil, increasing their strength dramatically. However these sheets of toughened glass were very small and it was not until the 1930s that sheets large enough for use in cars could be toughened.



            Laminated or toughened safety glass is now used all over the world in cars, buses, trains, aircraft, ships and shops and has proved its safety value.




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What is a glass made from?


Glass is made naturally from a fusion of silica (sand), soda and lime. This fusion can be achieved merely by lightning striking in a place where the right ingredients happen to be adjacent to each other. When glass is made by man, other ingredients are added, such as potash, lead oxide and boric oxide. Some of these ingredients are used to make glass clear, some to colour it, and others to give it a frosted effect.



      Glass was made by potters in Egypt for glazing stone beads as early as 12,000 B.C. As Egyptian culture progressed, craftsmen used glass for the manufacture of personal ornaments and bottles.



    A tremendous step forward in the use of glass was made by the Phoenicians in about 300 to 200 B.C. by the invention of the blow-pipe. The blowpipe is a hallow iron tube with a mouthpiece at one end and a knob shape at the other. The knob-shaped end is dipped into hot, viscous glass. A “gather” of molten glass can be blown by the worker into a hollow ball. The more he blows, the larger the ball.



    During the Roman civilization the art of glass-making reached near perfection. In the 3rd Century, the Romans cast glass on flat stones and produced the first window panes. The break-up of the Roman Empire and the ensuring Dark Ages brought an end to such cultural developments. The glazing of windows did not become wide spread over the whole of Europe until the 15th and 16th Centuries.



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What is glass fiber?


Glass fiber is a mass of very fine strands of glass. When ordinary glass is spun into thin threads it is strong and bendable, unlike normal glass objects, which are brittle and break easily.



       These silky strands of glass can be woven into a material or massed together like cotton-wool. Glass fiber does not decay or corrode. It is a good insulator and a poor conductor of electricity. Curtains made of this material do not rot in damp conditions or in sunlight. Now that technical dyeing problems have been overcome, glass Fiber can be patterned.



    Many plastics tend to crack or bend under stress or impact, but  combining them with strands of glass fiber results in very light, strong and useful materials. Glass fibre increases their strength in much the same way as concrete is reinforced with steel rods. These mixtures are moulded to make such things as aircraft parts, car bodies mats of glass fiber are used for filters and washers, and blankets of the material provide good in solution for houses.



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What is glass?



 



 



 



What have a window, a light bulb and a firefighter’s clothes got in common? They are all made from glass! This amazing material is all around you. It comes in lots of different shapes and sizes.



 



 



 



 





 



 



Glass is a very useful material.



Glass has many special features. Light can shine through glass and you can see through it. It is smooth and colourless. Glass does not let water through – it is waterproof. Glass does not rot or turn rusty. It’s easy to make smudges or marks on glass, but it is also easy to clean!



 



 


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What is glass made of?



 



 



Most of the glass that we use is made in a factory. It is made from a mix of sand and other materials. When the mixture is heated, it turns into a thick liquid that looks like see-through treacle. The hot liquid cools down and turns into hard glass.



 



 



 



 





 



Glass is made from natural materials.



Glass is made from natural materials – sand, soda and lime. These materials are cheap and plentiful, and found all over the world. They are dug out, or quarried, from the ground. Other materials are sometimes used to make certain types of glass. However, sand is usually the main ingredient.



 



 





 



 



 



Other materials are added to make special types of glass.



Adding other ingredients to the basic glass mixture makes different types of glass. Coloured glass is made when different chemicals are added to the glass mixture. Thin wires are sandwiched inside a cooling glass mixture to make wire glass which is very strong.



 



 



 





 



 



Some natural glass is found in the Earth.



Natural glass forms in the mouth of a volcano. The heat of the volcano melts sand and other materials to form natural glass, called obsidian. This glass was first used by humans to make very sharp tips for spears!


Making glass



 



Each type of glass is made in a different way. A piece of very thin glass is made in a different way from a strong glass bottle. The liquid glass may be cooled down quickly or slowly to make different kinds of glass. Glass can be shaped in many ways.



 



 





 



 



Flat, clear glass is called ‘float glass’.



In a factory, ingredients are measured and mixed and then heated up in a furnace (hot oven). As the mixture cools, it is shaped. To make glass for a window, the glass mix is spread over hot liquid metal. It is called float glass because it floats on the liquid metal. The contact between the glass and the metal is perfectly flat.



 



 



 



 





 



 



 



Glass is shaped when the mix is still runny and hot.



Glass cools quickly so it needs to be shaped before it sets and hardens. Glass can be shaped either by craft workers or special machines.



 



 





 



 



This bottle was shaped by a mould.



Liquid glass is poured into a mould. As it cools down, air is forced in to make the hollow. The glass hardens and is taken out of the mould.



 



 



 



 



 





 



 



Glass-making is skilled work.



Glass ornaments are often made by heating, joining and shaping several pieces of glass.



You can blow glass up like blowing up a balloon!



 


Clear or cloudy glass?



 



 



 



 



Glass is useful because it keeps the wind and rain out but let’s in light. Glass is naturally transparent. This means you can see through it. Glass can be made in beautiful colours. Glass can also be made cloudy so that you can’t see through it.



 



 



 





 



 



 



 



Glass is easy to see through.



Transparent glass is used everywhere, from windows to the glasses that people wear to help them see clearly. In the past, some windows were so thick that it was difficult to see through them! Thick glass is less clear than thin glass. Glass that only allows some light to pass through is called translucent.



 



 



 



 



 





 



 



 



You can’t see through some glass!



Some glass only allows through a small amount of light. This cloudy glass is called opaque. It is used when people don’t want others to see in. Opaque glass is often used on front doors or in bathroom windows.



 



 



 





 



 



 



You can make your own stained glass window!



Collect some coloured sweet wrappers. Ask an adult to help you cut a window frame from black card. Use black sticky tape to stick the wrappers in the window. Put your frame on a windowsill and see the colours as the Sun shines through!


Helpful glass



 



Imagine your house without glass – it would be very dark with no windows or light bulbs! Today, glass is used for many things from lights to camera lenses. It is even used to make material for clothes. Here we look at ways in which glass helps us.



 



 



 





 



 



 



Catseyes in the road shine in the dark.



 In the dark, tiny lights mark out the direction of the road. These lights are made from glass and metal beads. When light from a car shines on them, they reflect the light back and mark the shape of the road. The lights are called Catseyes because they shine in the dark like the eyes of a real cat.



 



 


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Strong glass



 



 



If you knock a light bulb it will shatter into tiny pieces. Glass can be very weak or very strong. Some glass shatters easily but glass can also be made strong enough to survive fierce knocks, wild winds and heavy hailstones!



 



 



 



 





 



 



This glass does not fly around when it is smashed.



Laminated glass is made like a sandwich with two layers of glass and a plastic filling. If laminated glass breaks, the pieces of glass stick to the plastic instead of flying around. This kind of glass is used on car windscreens for safety.



 



 





 



This canoe is partly made from glass.



Glass reinforced plastic is strong and hard. It is made by sandwiching glass fibre between layers of plastic. It can be easily shaped and is used to make builders’ hard hats, boats and the bodies of some cars and aeroplanes.



 



 



 





 



 



 



This rocket has a glass nose!



When a space rocket blasts into space, it gets extremely hot. Many materials crack at such temperatures. A special glass called glass-ceramic can survive these temperatures without damage. The tops of most electrical ovens are now made of glass-ceramic. Glass-ceramic was actually discovered when glass was overheated by mistake!


Glass and heat



 



 



 



 



 



Glass can keep heat inside a building. A glass greenhouse lets in the Sun’s heat to help plants grow. Double glazing can help to keep a house warm. A layer of fiberglass padding can be put in the loft or attic of a house. It keeps the house warn in winter.



 



 



 



 





 



 



 



Some glass does not crack when heated.



The glass in this lantern is heat-resistant. You may have heat-resistant glass jugs, bowls or dishes in your kitchen. Ordinary glass cracks and breaks if boiling water is poured in or put over heat. Glass made with a special chemical does not break when heated. This is useful for glass cooking pots.



 



 



 



 





 



 



 



 



Mirrored windows help save energy.



Mirrored glass reflects a lot of the Sun’s rays and can stop buildings in hot countries from getting too hot. Double glazing and fiberglass are used to keep houses cool in hot weather and warm in cold weather.



 



 



 



 





 



 



 



A thermos flask keeps your drink hot or cold.



Glass is used inside a thermos flask. A drink is poured inside a glass container. The glass inside is covered with silver to stop warmth or coldness escaping. Another silver glass layer stops any coldness or warmth entering the thermos flask.


Glass for seeing



 



 



Do you wear glasses, or have you ever used a magnifying glass to see a tiny insect? Special pieces of glass are used to help us see more clearly. They are very clear and are made in a curved shape. They are called lenses. Glass lets us see images of ourselves as well.



 



 



 



 





 



 



 



Some glass can make tiny things look bigger.



Look at a bug under a magnifying glass and it will look much bigger! The glass used in microscopes and magnifying glasses is called optical glass. Rays of light pass through the optical glass of the lens in such a way that it makes the image look bigger. This is called magnifying.



 



 





 



 



Glass in telescopes helps you see far away into space.



Telescopes help us see things that are far away. Special optical glass lenses or mirrors in telescopes gather lots of light. This brings the picture of faraway stars and planets closer to your eyes.



 



 





 



 



What do you see in the mirror?



Take a look at yourself in a mirror. Mirrors are made of very shiny glass and have a layer of silver on one surface. Mirrors send back lots of light to your eyes. This lets you see a reflection of what is facing the mirror.



 


Special glass



 



Have you ever wondered how your computer works? The answer is with the help of glass! Pieces of glass can be made into tiny threads, thinner than a single piece of hair. These are used to send messages between some computers and telephones.



 



 



 



 





 



 



Thin pieces of glass can send messages.



Glass can be made into an optical fibre. This is a rod made of a very thin glass tube, coated in a layer of plastic. Lots of fibres are bundled together in cables. The fibres send light messages and pictures around corners. Flashes of light pass down the optical fibre. These flashes of light are like a code.



 



 


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Beautiful glass



 



 



Glass is not only useful. Glass can be made into works of art. It can be turned into beautiful shapes, patterns and colours. Words can be written on glass using tiny drills. It takes great skill to make, cut and pattern glass, without breaking it!



 



 



 



 





 



 



 



Crystal glass sparkles in the light.



Have you ever seen a glass that seems to sparkle in the light? This glass is called crystal glass. To make crystal glass, a metal called lead is added to the liquid glass mixture. When the glass sets, craft workers can cut tiny shapes into the crystal glass.



 



 



 



 





 



 



 



You can cut patterns into glass.



An artist uses a small drill to draw patterns on glass. This is called engraving. To write on glass, the artist draws letters with a thin needle. A chemical is used to carve the shape more deeply into the glass. This is called etching.



 



 



 



 



 





 



 



Turn a jam jar into a beautiful vase.



Ask an adult to help you make a vase. Take care – glass breaks easily and is sharp. You need a clean empty jam jar, paints and a paintbrush. Put your jar on an old newspaper. Carefully paint a pattern on the jar. Leave the paint to dry. Varnish over the paint – you have a beautiful vase.