Question

The method used for cooling the glass is known as
A. Rapid heating
B. crystallization
C. annealing
D. all of the above

Answer 1

Hint: The making of glass demands to make it durable and with high strength as to not easily break the glass. Therefore cooling of glass is employed to make it resistant to physical stresses. This is done to make the glass durable for temperature changes.

Complete answer:
The glass is made up of particles of sand, which are called silica, or silicon dioxide. This makes the glass temperature dependent. It expands with exposure to heat and compresses when exposed to colder temperatures. This temperature variation creates stress in the glass texture and affects its strength. To make the glass durable over a wide range of temperature, it is subjected to cooling.
The cooling process of glass is known as annealing. It consists of cooling the glass slowly inside a kiln at a temperature called annealing temperature, until it reaches room temperature. The annealing of glass allows it to cool the glass surface including the interior in a uniform manner which makes it stress free. This also removes internal stresses. On the other hand, if the glass is allowed to cool rapidly, then it does not cool in a uniform manner creating strain in the glass.
Hence, the cooling of glass by a slow cooling method is called annealing.

So the correct answer is option C.

Note:
Rapid heating is not required, rather glasses are cooled after making them to make them more durable to stresses. Crystallization is the process through which new crystals of any substance arise due to association of the substance. Glass formed by annealing is called annealed glass.