Impressions - June/July 2021 - 39

Shown is an artworkdetail
comparison. The
skull on the left printed
with regular ink and
the skull on the right is
printed with puff. Note
the loss of detail on the
puff print side.
or blocked by the film-positive portion, decreasing the chances of
overexposure and loss of detail. This is never more important than
when exposing thick emulsions.
Remember the following tips about film media options:
1. Vellum is one of the lowest-quality types of film positives.
The translucent white is not clear and acts as a filter, while the black
print is not very opaque. Vellum is not ideal for transferring detailed
art to a screen, but it works well under certain conditions - such
as one- or two-color jobs that are not as particularized.
Vellum also can shrink when heated, such as when it goes through
a laser printer. Therefore, it's not recommended for prints requiring
exact registrations. When using vellum, you can achieve a darker,
more opaque black print by using a spray fixative, which " fuses " the
toner particles to make the printed areas appear darker.
2. Inkjet films often work much better than vellum. The
black positive portion can become very black and opaque under
the correct printer settings, and the screen positive's film portion can
be purchased in a clear version. In addition, these films are readily
available and don't shrink when heated during the printing process.
3. Real Ortho Litho film and printers are the highest-quality
option. For four-color jobs and prints where perfect registration
is important, consider switching to Ortho film. This process costs
more, as it involves more expensive films and chemicals; however,
if you're dealing with detailed artwork and exact registrations,
it's worth it.
Emulsion, Emulsion, Emulsion
Good emulsion coverage will prevent many issues, including lack
of ink opacity, and uneven coverage and edges. There is an absolute
correlation between the print quality and the tools used.
When printing special effects, emulsion is paramount. For example,
glitter or shimmer inks also need a thicker deposit due to
the metallic flakes they contain. Similarly, when printing a puff or a
texturing ink (such as an HD or granite-type ink), a thick ink layer
will allow the effect to truly come to life.
A starting measurement for determining whether there is enough
emulsion covering the screen is emulsion over mesh (EOM), which
measures the emulsion thickness of the coated screen vs. the uncoated
screen. A typical average EOM is 20%.
A thicker emulsion coating really counts on the bottom of the
screen's shirt side. When using finer mesh counts, less emulsion
typically is applied, but it still is important to have more emulsion
applied to the bottom of the screen. Always remember that just as
the mesh controls ink flow, it also controls emulsion flow.
When printing HD, gel, or thick granite-type texturing inks,
it's often more convenient to use a capillary film for instant, thick
emulsion coverage rather than applying numerous coats. Once you
learn how to work with capillary film, you'll find it easy to apply
and it can save valuable time in screen prep.
Squeegee Picks
A simple switch to either a harder or softer squeegee can be the
difference between whether the print turns out " OK " or " great. "
I've heard printers asking suppliers for squeegees and referencing
them by color. This makes me cringe because different manufacturers
offer different colors for various durometers. One brand's yellow
blade at 60 durometers may be another brand's 80-durometer blade
color. Order squeegees by referencing the durometer hardness to
ensure you receive the correct type.
Blade shapes include square, round and V-shaped. Square, or
Just as the mesh
controls ink flow, it also
controls emulsion flow.
JUNE/JULY 2021
P.39
Impressions - June/July 2021

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