BK7, a borosilicate crown glass, has a refractive index of 1.53-1.51 in the visible range of 400-700nm. It is useful for measuring angular dispersion according to Snell's law. It is also superior to acrylic for showing that near infrared light (NIR) can be separated to heat a thermometer. For optical systems requiring much greater dispersion, flint glass is the material of choice.

The angle between the two polished faces of a triangular prism is called the refracting angle or apex angle. For transmitted rays in dispersion prisms this angle is 60°. Right angle optical prisms, the critical angle is 90°.One prism face can be "silvered" & made into a mirror to reflect light 90° for laser laser beam steering. When the opposite face is also silvered, to enhance total internal reflection, light is retroreflected 180°.