Chandana Chandra explains: Light falling on an object either gets reflected or transmitted through it. The objects that reflect light are said to be opaque, while those that transmit light are termed as transparent bodies.

In general all liquids have been observed to be transparent. However, unlike liquids and gases solids are usually opaque due to their organised atomic structure.

The atomic structure of glass is almost the same as that of liquids (the atoms being arranged in a random fashion). Hence glass is often termed as super-cooled liquid or pseudo liquid.

“When light falls on a crystalline material it gets heavily scattered by the its external as well as internal surfaces. As no light is allowed to pass through the material it results in opaqueness. But glasses don’t have any rigid boundaries or internal surfaces (due to its random arrangement of atoms). So light infringing on it simply passes through the material”, said Dr H.S. Maiti, director of Central Glass & Ceramic Research Institute (CGCRI), Calcutta.

However, glass also scatters light to a certain extent particularly from its external surface. “It must be noted that glass will be transparent provided the external surface is highly polished to minimise the scattering of light. From this point of view, any glass having a ground or rough surface is no longer transparent but translucent,” he added.

The question was sent by Suhas Sinha Ray from Jamshedpur