short, or when graphic equipment is unavailable. When not required to work under these constraints,
mechanical/chemical processing provides you a more professional and durable product.
(1) The diazo process. The diazo process is the most commonly used method for producing
top quality viewgraphs for briefings and training materials. The term "diazo" refers to organic emulsion,
which creates color through exposure to light, and the development of the image on film by using
ammonia. The diazo process makes use of specially treated films and paper, and a diazo process printer
to expose and develop these materials.
(2) How the diazo process works. Diazo film, or foils, and the paper are treated with a
mixture of diazo salts and an azo dye. These salts are sensitive to light, especially ultraviolet light.
When you expose the film to ultraviolet light, it chemically changes so that no image appears. If the
coating is not exposed, and is developed in an alkaline medium, the diazo salts combine with the azo
dyes to form a color image. Through the use of various dyes, you may create many colors on the
acetate. Figure 2-2 illustrates how the chemical reaction of the diazo emulsion, when exposed to
ultraviolet light and developed using ammonia, forms images on the film.
(3) Using the diazo process. There are three major operations involved in producing VGTs
using the diazo process:
(a) Preparing the diazo masters.
(b) Exposing and developing the diazo film.
(c) Mounting the diazo transparency.
PART B - MAKE A VGT WITH THE DIAZO PROCESS
4. Preparing the Master.
One of the keys to successful diazo VGTs is the materials you use to prepare your master. A diazo
master works on a principle that opaque image areas prevent ultraviolet light from striking the diazo
film, while nonimage areas let the light through to expose the film.
With this in mind, the base material for the diazo master should be made of transparent film or
translucent paper. Use a high quality tracing paper. Select a paper grade with a fine fiber texture, and
use the same kind for all masters. This eliminates changing exposure times.