The most commonly used dot shapes used when outputting positives
are: round, square, diamond, and elliptical. The most effective
for silkscreen printing are the diamond and elliptical.
Choice of Halftone Dot Shape
Taking a closer look at the positive you will see that the dots
are formed in regular rows, with each one "growing" outwardly
from the centre. The size of each dot will depend on the lpi (lines-per-inch)
setting selected when outputting the positives.
The choice of dot shape for silkscreen printing is most important
when looking at the midtone range of the finished print. At this
point in the tonal range of the design, the dots begin to join up
causing them to "bleed" into one another - this is known
as dot gain. The amount of dot gain can also be effected by various
print production conditions, to name a few: - incorrect screen exposure,
the choice of ink and viscosity, squeegee pressure and shore.