The Application of Diazotype Color Films to the Production of Projection Slides of Electron Microscopic Material

In general, in the production of projection slides, one is limited to the use of s tandard lantern slide plates. If the original electron micrograph negatives vary in contrast, it is often difficult to produce, within an acceptable range of density, a series of slides for projection. In an a t tempt to overcome this difficulty, diazotype color films have been tested as an alternative to the standard lantern slide plates. The light-sensitive chemical compounds in diazotype color films belong to a large class of benzene-derived compounds known as diazonium salts in which one of the hydrogen atoms in the benzene ring has been replaced by two atoms of nitrogen. In the presence of an alkaline agent such as ammonia, diazonium salts react with coal tar derivatives, usually phenols or aromatic amines (commonly referred to as "couplers" in this process), to form azo dyes. When a diazonium salt is exposed to ultraviolet light, it loses its nitrogen atoms and becomes converted to a colorless phenol incapable of coupling to form a dye. Today, the use of diazotype papers virtually has replaced the use of ferroprussiate papers for the reproduction of technical drawings and similar materials.