The glass material are very much renowned because of the non-reactive nature it has. Because of that reason, it has been the foremost choice of many industries, like pharma, chemicals and what not. The glass material has a very brittle nature and due to which while their production process they get volatile in nature and exhibit some amount of strains within. These types of stress or strain distribution may not be visible by human eyes but are there always and be the major reason behind future cracks or breakage.
The strain distribution are such defects that may remain in the glass material for long and you will just not get to know about it. But the good part is that it is detectable. There are several machine which can easily detect the polarization of light when they passes through a stress section of glass. While doing that, light makes some patterns on the glass which can be visible with naked eyes. These machine are called as Polariscope strain viewer for glass.
The machine is equipped with a light source and a large viewing area. You can place the glass material on that area and let the polarized light pass through it. When this happens you will see some multi colored patterns on the glass and note them. Then you need to compare these patterns with the chart displaying all types of possible defects. By this the manufacturer can easily evaluate the defect.
There is another reason for establishing such type of testing system that is the experience of sudden heat and cold in glasses while transporting them. The glasses can exhibit such type of defects when they undergo sudden experience of extreme heating and extreme cold. At this position they generate the stress distribution on any part of the glass which can be difficult to detect without the testing apparatus.