Glass has several key properties including its ability to transmit, absorb, or refract light without having a definite crystalline structure. There are different types of glass such as soda lime glass, potash-lime glass, potash-lead glass, and borosilicate glass which are used for various purposes. Glass is manufactured through a process involving collection of raw materials, batch preparation through mixing, melting in furnaces, fabrication into desired shapes, and annealing to slowly cool the glass.

1. glass
CONTENT
1. PROPERTIES
2. TYPES OF GLASS
3. INDUSTRIAL FORMS OF GLASS

2. Properties of glass
1. It absorbs, refracts or transmits light.
2. It can take up high polish and may be used as substitute for very costly gems.
3. It has no definite crystalline structure.
4. It has no sharp melting point.
5. it is an excellent electrical insulator at elevated temperature due to the fact that
glass can be considered as an ionic liquid. The ions are not easily moved at room
temperature because of high viscosity. But when the temperature rises, the ions
are permitted to flow and thus they will sustain as electric current.

3. Properties of glass
6. It is affected by alkalies.
7. It is available in different colours.
8. It is not usually affected by air or water.
9. It behaves more as a solid than most solids in the sense that it is elastic. But when
elastic limits is exceeded, it fractures instead of deforming.
10. It is not easily attacked by ordinary chemical regents.

4. Types of glasses (based on commercial
point of view
Soda lime
glass
Potash-lime
glass
Potash-lead
glass
Borosilicate
glass

5. Soda lime glass (commercial glass)
 It is mainly a mixture of sodium silicate and calcium silicate.
Properties-
1. It is available in clean and clear state
2. It is cheap
3. It is easy fusible at comparative low temperatures.
4. It is possible to weld or blow articles made from this glass with the help of simple
source of heat.
Uses- it is used in manufacturing of glass tube, and other laboratory apparatus, plate
glass, window glass, etc.

6. Potglassium-lime glass
It is mainly a mixture of potglassium silicate and calcium silicate.
Properties-
1. It fuses at high temperature
2. It is not easily affected by water and other solvent.
3. It does not melts so easily
Uses - this glass is used in manufacturing of articles which have to withstand high
temperature such as combustion tubes, etc.

7. Potglassium-lead glass
It is mainly a mixture of potglassium silicate and lead silicate.
Properties –
1. It fuses very easily
2. It is easily attacked by aqueous solution.
3. It possesses bright lustre and high refractive power
4. It has specific gravity of 3 - 3.30
5. It turns black and opaque, if it comes in contact with reducing gases of the
furnace while heating.

8. Borosilicate glass
This type of glass is in the form of ovenware and heat resisting ware.
It is made up of mainly 70% - 80% silica and 7% - 13% boric oxide with smaller amount of alkalis (sodium
and potglassium oxides) and aluminum oxide.
Properties –
1. It has a relatively low alkali content and consequently high durability and thermal shock resistance.
2. It has high softening point
3. It does not break when temperature changes quickly.
Uses – this glass is widely used in chemical industry, for laboratory apparatus, for ampoules and other
pharmaceutical container, for various high intensity lighting application and as glass fibres used in the
reinforced plastic to make protective helmets, boats, piping, car chglassis, ropes, car exhausts and many
other items and also textile industry.

9. Common glass (special type of glass)
It is made of cheap raw material.
It is mainly mixture of sodium silicate, calcium silicate and iron silicate.
Properties –
1. it fuses with difficulties
2. Its is brown, green and yellow in colour.
3. It is easily attacked by acid.
Uses- it is mainly used in manufacturing of medical bottles.

10. Manufacturing process of glass
There are five stages of manufacturing glass –
1. Collection of raw material
2. Preparation of batch
3. Melting in furnace
4. Fabrication
5. Annealing

11. Collection of raw material – depending upon the type of glass to be manufactured, suitable materials are
manufactured.
In addition to raw material cullet and decolourisers are also added for each type of glass.
S NO. Types of glass Raw material
1 Soda-lime glass Chalk, soda ash and
clean sand
2 Potash-lime glass Chalk, potglassium
carbonate (K₂CO₃) and
clean sand
3 Potash-lead glass Litharge(PbO lead
monoxide ) or lead
sesquioxide (Pb₃O₄),
potglassium carbonate
and pure sand
4 Common glass Chalk, salt cake
(Na₂SO₄), coke, ordinary
sand, etc.

12. Cullet – it indicates waste glass or pieces of broken glass.
 They increase the fusibility of glass and prevent loss of alkali by volatisation during the reaction in forming new
glass.
 They also reduce the cost.
 The raw material generally contain traces of the iron compounds. The ferrous oxide imparts a green colour to
glass and ferric oxide imparts a very light yellow tint. To avoid such effects, the decolourisers are added.
Examples of decolourisers are antimony oxide (Sb₂O₃), arsenic oxide (As₂O₃), cobalt oxide (CoO), manganese
dioxide (MnO₂) and nickel oxide (NiO).
2) Preparation of batch – the raw material, cullet and decolouriser are finely powdered in grinding machines.
These materials are accurately weighed in correct proportion before they are mixed together. The mixing of
these materials is carried out in mixing machines until a uniform mixture is obtained. Such a uniform mixture is
known as the batch or frit.
3) Melting in furnace – the batch is melted either in a pot furnace or in a tank furnace. The heating is continued
until the evolution of carbon dioxide, oxygen, Sulphur dioxide and other gases stops.

13. 4) Fabrication – the molten glass is given suitable shape or form in this stage. It can either be done by hand or
by machine. The hand fabrication is adopted for small scale production and machine fabrication is adopted for
large scale production.
Different ways of fabrication –
1. Blowing
2. Casting
3. Drawing
4. Pressing
5. Rolling
6. Spinning
5)Annealing – the glass articles, after being manufactured, are to be cooled down slowly and gradually. This
process of slow and homogeneous cooling of glass articles is known as the annealing of glass.
it is a important process. If glass articles are allowed to cool down rapidly, the superficial layer of glass cools
down first as glass is a bad conductor of heat. The interior portion remains comparatively hot and it is therefore
in a state of strain. Hence, such a glass article breaks to pieces under very slight load .

14. Method of annealing
1. Flue treatment
2. Oven treatment
Flue treatment – in this, a long flue is provided and it is constructed in such a way that
there is gradual decrease in temperature from one end of flue to the other. The red-hot
articles of glass are allowed to enter at the hot end of flue and they are slowly moved on
travelling bands. They become cool when they reach the cool end of flue.
 This method is useful for large scale production.
Oven treatment – in this, the red-hot glass articles are placed in ovens in which
arrangement is made to control the temperature. After articles are placed in the ovens, the
temperature is slowly brought down.
 This method is useful for small scale production.

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