What are different types of Glass?

The approximate composition of ordinary glass is given by the formula, Na2O. CaO.6SiO2. The raw materials required for the manufacture of ordinary glass are sodium carbonate, calcium carbonate and silica. The raw materials are ground separately to a fine powder, weighed accurately and mixed in a definite proportion. The mixture is called batch.

A specific amount of cullet (broken pieces of glass) is added to increase the fusibility of the glass produced The mixture is heated in fire clay pots or in a tank furnace. The pots (or tanks) are heated by using producer gas. The burning of gases produces a high temperature of about 1673 K in the furnace. The raw materials present in the batch melt at this high temperature and react with one another to form glass. Carbon dioxide is evolved during the reaction.

Annealing of Glass

The slow and uniform cooling of Glass is called Annealing. The glass articles are made by pouring molten glass into moulds and then cooling. If the glass is cooled rapidly, it becomes very brittle and cracks easily and if it is cooled very slowly, it becomes opaque. Therefore, it should be cooled neither very slowly nor very quickly. In the annealing process, the hot glass articles are placed on a slow moving belt which passes through a long narrow chamber in which the temperature is regulated carefully so that it is hot at the starting point and at room temperature at the other end. It takes several days for completion.

Soda glass or soda-lime glass

It is the most common variety of glass. It is prepared by heating sodium carbonate and silica. It is used for making windowpanes, tableware, bottles and bulbs.

Coloured Glass

Small amounts of metallic oxides are mixed with the hot molten mixture of sand, sodium carbonate and limestone. The desired color determines the choice of the metallic oxide to be added, as different metallic oxides give different colors to the glass.

Chemicals Used in Making of Colored Glass
  • Iron oxide is used to produce bluish-green glass (used in beer bottles).  Chromium along with Iron Oxide gives richer green color, used for wine bottles.
  • Sulfur + Carbon + Iron salts make iron polysulfides, which give amber glass ranging from yellowish to almost black.
  • In borosilicate glasses rich in boron, sulfur imparts a blue color. With calcium it yields a deep yellow color
  • Manganese is added to remove the green tint given by iron. Manganese dioxide, which is black, is used to remove the green color from the glass; in a very slow process this is converted to sodium permanganate, a dark purple compound.
  • In New England some houses built more than 300 years ago have window glass which is lightly tinted violet because of the above chemical change; and such glass panes are prized as antiques
  • Small concentrations of cobalt (0.025 to 0.1%) yield blue glass.
  • 2 to 3% of copper oxide produces a turquoise color.
  • Nickel, depending on the concentration, produces blue, or violet, or even black glass.
  • Lead crystal with added nickel acquires purplish color.
  • Nickel together with a small amount of cobalt was used for decolorizing of lead glass.
  • Uranium (0.1 to 2%) can be added to give glass a fluorescent yellow or green color. Uranium glass is typically not radioactive enough to be dangerous, but if ground into a powder, such as by polishing with sandpaper, and inhaled, it can be carcinogenic. When used with lead glass with very high proportion of lead, produces a deep red color.
 Safety glass

It is made by placing a sheet of plastic such as celluloid between sheets of glass.

Laminated glass

It can also be called bulletproof glass. Several layers of safety glass are bound together with a transparent adhesive.

Flint Glass

Optical glass is softer than any other glass. It is clear and transparent. Potassium and lead silicates are used in making optical glass. It is also called flint glass. The main use of flint glass is in the manufacture of lenses, prisms and other optical instruments.

Pyrex glass

Pyrex glass is highly heat resistant. In ordinary glass, silica is the main constituent. In pyrex glass some of the silica is replaced by boron oxide. Boron oxide expands very little when heated, thus, pyrex glass does not crack on strong heating. Pyrex glass is also called borosilicate glass. It has a high melting point and is resistant to many chemicals. Laboratory equipment and ovenware are made of pyrex glass.

Photo-chromatic glass

Photochromatic pr Photochromic glass acquires a darker shade when exposed to bright light and returns to its original lighter shade in dim light. This happens because silver halides (iodide or chloride)  is added to this glass. Plastic photochromic lenses rely on organic photochromic molecules (such as oxazines and naphthopyrans) to achieve the reversible darkening effect.

Lead crystal glass

Lead crystal glass has high refractive index, and so has the maximum brilliance. It sparkles and is used for high quality art objects and for expensive glassware. It is also called cut glass because the surface of the glass objects is often cut into decorative patterns to reflect light. In order to increase the refractive index, lead oxide is used as flux in crystal glass, therefore it is also called lead crystal glass.


1 Comment

  1. mithun

    March 26, 2019 at 2:08 am

    this is awesome article. It helped me to clear the concept of various kinds of glass.

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