Diazo materials are available from various sources under different trade names and desig-nations, such as K&E, 3M, and GAF. Basically, all diazo reproduction materials have been coated with a light-sensitive dye. The two types commonly used for reproduction of original drawings are standard weight blueprint paper and sepia line intermediates.

Standard weight paper (commonly called blueprint paper) provides a black or blue image on a white background. The printing speed for paper is described as rapid. Paper is available in sheet sizes that range from 8 by 10 in. to 34 by 44 in., or in rolls that range in widths from 11 to 42 in. with lengths of 50 or 100 yd.

Colored paper provides black or blue images on blue, green, pink, or yellow stock.

Plastic-coated papers are now available that give a slightly glossy print with better line density than the standard paper.

Sepia line intermediates are used as duplicate originals. These intermediates are prints from which additional prints can be made, saving wear on the original. When you use the sepia inter-mediate, it is possible to keep emulsion-to-emulsion contact in each generation, resulting in a sharper image. In addition, sepia has a greater density and is capable of delivering a darker image than the original, particularly when the original is in pencil. Sepia has a rich, mahogany image color that blocks the ultraviolet light rays. Base materials may be a vellum base treated with a plastic transparentizer that allows the passage of the light rays. Sheet and roll sizes are similar to those of the standard paper. You can make corrections on the sepia prints by using a solution of intermediate corrector to remove the image, then adding the pencil or ink correction.