Sight glasses are made as circular discs, squares, shaped and tubular form from sheet glass transparent materials or fabricated from optical glass materials. Optical materials include fused silica, quartz and sapphire, which are lapped and polished, custom made to specification on thickness and dimensions. When selecting a sight glass for your application, there are many factors to be considered:

·glass type

·chemical resistance

·tensile strength

·maximum working temperature

·specification of edge

·usable working area

·tolerance of housing/holder

Sight glasses are used for chambers, chemical, furnace scientific and research apparatus and are subjected to many hostile and demanding environments.