Glass bottles are made using molds. Molten glass is dropped into a mold and compressed air forces it to take the shape. It is then transferred to another mold to give it its final shape. Float glass is used in windows and doors. It is made by melting raw materials in high heat furnaces. The molten glass floats on molten tin and is smoothed by its surface. It is cooled on rollers in controlled temperature zones. The properties of glass can be changed by adding chemicals during the manufacturing process. For example, adding selenium sulfide produces red glass, copper oxide makes blue glass, and alumina or phosphate creates milky glass.

1. GLASS MANUFACTURING
How are glass bottles made?
To make glass bottles, moulds are used. A lump of molten glass is dropped into the mould. A
rush of compressed air forces the molten glass to reach the bottom of the mould. Due to the
pressure of the compressed air, the glass sticks to the sides of the mould and acquires it's shape.
This is then transferred to another mould where it is given the final shape of the bottle or any
other special shape desired.
Float Glass
Float Glass is used in windows, glass doors, table tops etc. Making glass for windows is a tough
task. The glass has to be absolutely smooth and clear without any distortions. One way of
making this glass to flatten it between rollers , however the sheet so formed is not perfect. A
better way to manufacture perfect glass is by the float glass method. Raw materials used in the
manufacture of glass such as Sand, Waste Glass and Calcium Carbonate is introduced into the
furnace. The temperature in the furnace is around 1400 degrees centigrade. Due to this high
temperature the raw materials melt and combine to form molten glass. This molten glass is made
to float on a stream of moving molten metal, such as tin. The molten metal is very smooth and
hence the glass floating on this molten metal also becomes very smooth. The molten metal is
kept in an atmosphere free from oxygen in order to prevent the formation of metal oxide which
could cause the glass to be uneven in shape. The glass is carried forward by rollers which take it
through different temperature zones so that cooling is achieved.

2. Changing the properties of Glass
The properties of glass such as its color can be changed by adding chemicals. for example red
colored glass can be obtained by adding selenium sulfide, blue glass can be obtained by adding
copper oxide and milky glass can be obtained by adding alumina or phosphate. Green tint in the
glass can be removed by adding cobalt and selenium oxide.