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When should I
There is a tool for every
job, and vellum is not the right tool for every screen printing job
you might encounter. While vellum is a very inexpensive exposure positive
for most jobs, and can beautifully handle roughly 80% of screen printing
jobs, there are still those 20% of screen printing jobs performed by
garment printers that are not a good candidate for vellum use.
Vellum has the following
benefits as a screen exposure positive for screen printing:
- Extremely low material
cost - SMR Premium Vellum sheets cost as little as 1/15 the price of some
of their film-type product counterparts.
- Rapid delivery -
Processing vellum sheets is as easy as printing the design in your
computer printer. With traditional film, you will still need additional
equipment to create and process the design on film. You will also spend
roughly 10 - 20 additional minutes to expose - develop the film and you
will have to wait for the film to dry.
- Low overall cost - SMR
Premium Vellum costs roughly 11 cents per 8.5" x 11" sheet when bought in
packs of 500. Traditional film costs around $1 per sheet this size,
requires additional equipment to process, requires roughly 50 cents worth
of chemicals to process, and uses an average of 20 minutes total labor
time to process. In all, a traditional film positive of this same size
costs about $5.
As a paper-based product,
vellum has the following shortcomings:
- Shrinkage - Vellum can
be shrunk slightly by the heat of laser processing, or distorted slightly
by moisture in large solid areas printed by ink-jet printers.
- Opacity - The opacity of
a vellum positive can only be as good as the computer printer used to
create the image carried by the vellum positive. See
Printing with Vellum and
Vellum Tips & Tricks for tips on optimizing
- Alignment - Vellum is
usually printed by off-the-shelf computer printers, which may or may not
be able to perfectly adhere to the dimensions of the originally intended
design. In short, if your computer printer is not sufficiently accurate to
output 2 separations that will line up, no matter what the printed media,
you'll never get vellum separations that line up either. Any shrinkage or
distortion factor caused by the printing process will not likely help
alignment either. In contrast, film output devices are designed to be
In short, Vellum is a
great, inexpensive medium to use in screen making for:
- Nearly all single color
- Multi-color jobs where
perfect alignment is not super-critical.
- Screen meshes that do
not require extreme exposure times. (Jobs using 20 mesh monofilament or
dimensional printing buildups might be a problem)
Vellum will probably not be
a good choice for:
- 4-color process jobs or
tight index color separations.
- Jobs where exact
measurements are critical - such as printing rulers or other measuring
- Jobs where extremely
long exposure times are needed due to the thickness of the emulsion, if
your printer cannot lay down a very dense image.
For jobs where vellum will
not suffice, printers should use film positives or dry-film positives.
Despite the much higher expense of using these mediums, film products offer:
- Total light blocking in
- No shrinkage factor.
- Extremely accurate image
placement and dimensional integrity.