An optical grade teleprompter mirror is created by dipping large sheets of low iron glass (color neutral) into a solution of dielectric filters (nanotechnology), which is then baked on for a permanent, highly durable bond. The dielectric mirror allows a precise percentage of the light to pass though while reflecting the remainder. Before the use of dielectric coatings, the old fashioned way of making beamsplitter glass was to apply a thin layer of silver nitrate and other metals (to prevent oxidation/tarnishing). This technique worked fairly well, but the resulting mirrors were tinted and easily scratched.