In recent times, the silicon dioxide (silica) coating has been found variety of applications ranging from gas diffusion barrier coatings to tribological coatings. In this invention, silica coating along with Cr has been developed for measuring the film thickness of lubricants optically. And the product is a fine polished glass disc of 10 mm thick and 100 mm dia. coated firstly with a thin layer of chromium (Cr) followed by a thicker Silica layer using Magnetron Sputtering technique.