Many thanks to Bruce Heller for the following explanation of how the DTB filters were used in the Technicolor dye transfer printing process: This blue filter is a sample of a rough ground Corning Glass DTB (Dark Theater Blue) filter. The example shown here has not been polished. These filters were used in the optical printing process for manufacturing both the 2-color and 3-color matrices used in Technicolor’s dye transfer printing process for theatrical release prints. When polished, these filters were used on Technicolor’s specially built optical printers, and were placed in the light path as contrast control filters for use with their special orthochromatic matrix printing film stock. The Corning DTB and LB (lantern blue) glass filters were ground and polished in sets ranging in thickness from .010” to.187”. These filters were used exclusively for the 2-color and 3-color printing of the matrices for the dye transfer process. No other filters were used.