Category Glass

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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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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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 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!

 

 

Continue reading “What is glass?”

 

 

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!