Borosilicate Crown Optical Glass (BK-7) is the most used technical optical glass for high quality optical components in the visible and near IR range. It possesses the high linear optical transmission in the visible range and down to 350 nm in the ultraviolet. BK7 has a high homogeneity with a very low amount of inclusions and is almost bubble-free. Its appearance is very clear and colourless. BK7 is relatively hard and shows a good scratch resistance. The chemical properties of BK7 are very stable, that's why special treatment to grind and polish isn't required, thus reducing manufacturing costs. BK7 is widely used for production of windows, prisms, lenses, mirror substrates and other optical items.