(2) Prepare the master with at least two registration marks. Locate the register marks in
opposite corners of the master. Position the marks so that they lie outside of the aperture form so that
they do not project onto the screen (see figure 2-3).
b. Materials. Tracing paper is the basic material used for diazo masters. Translucent paper lets
light pass through easily and provides a desirable working surface for pencil or ink.
Figure 2-3. Master register marks
(1) Drawbacks of translucent tracing paper. Although translucent tracing paper makes good
masters, it does have certain drawbacks. When used for color separation, it is hard to see through,
especially when preparing several overlays. It tends to wrinkle when you apply tape or large amounts of
ink to the paper. Also, the exposure time is relatively slow in the reproduction step.
(2) Mylar, an excellent master material. Mylar, a transparent polyester film, is an excellent
master material. Being transparent, it allows maximum light passage and facilitates color separation well.
Mylar is dimensionally stable and holds adhesive tapes, paste-up letters and symbols, or other
photographically reproduced images firmly on the film. Mylar also is available with a matte surface.
The matte surface is porous, making for easier and better inking.
c. Colors. If your VGT requires more than one color, you must prepare a separate master for
each color, using a process called color separation.
(1) Using too many color sheets per viewgraph affects the amount of light projected,
resulting in a dull image. You should not exceed five sheets per viewgraph.