Conventional methods of making line drawings from photographs not suitable for reproduction consist, in general, of inking in desired features on a large print of the photograph, usually blue, and then bleaching out the photographic image. This procedure, which gives good results in skilled hands, produces a line image consisting only of the applied ink lines, which are usually somewhat degraded because the paper fibers are displaced (“exploded“) by the chemical action of the bleaching solution. This same chemical action makes difficult additional ink work after bleaching.

High-contrast films developed during the last decade make possible several simplifications of this procedure. When the ink work on a blueprint is satisfactory (as determined by viewing through a deep blue filter), the print, as is, may be sent to the engraver, with instructions to “drop out the blue,” which he does by using a high contrast “color blind” emulsion, such as Kodalith.