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Because screen printed graphics is specialized and singular pursuit it employs
it's own terminology and code of standards. The following is a list of anomalies
that are generally considered to be defects in workmanship. While these problems
are caused by difficulties inherent in the process, you have a right to expect
not to see them in your finished product.
Pinholes are tiny breaks in the emulsion that coats the screen and appear
as small dots of ink where there ought not to be any. While an occasional
pinhole will be missed by the most meticulous of printers they can be easily
removed,(except in garment dyed shirts), with what is known as a spotting
gun.
Stains on the garment can be caused by a variety of factors. The printer
could get a little over zealous about his inking or the folders could have
a Java disaster or the mill could leak a bit of machine oil during the sewing
process. Stains are clear defects and the printer should be informed about
even subtle discolorations on the garment.
There are general rules for placement of an image on a garment, but since
all garments are of varying dimension and proportion, exact placement can
be a judgment call. It also depends on the size and shape of the image itself.
The rules of thumb are: Full front- 3-4 inches down from the collar. Full
Back- 4-6 inches down from the collar. Left Chest- Bottom aligned with bottom
seam of sleeve.
All of these are general rules. In the end it is a an aesthetic decision
on the part of the printer. If you have an intended placement that deviates
significantly from the above guidelines then you should make it clear to
the customer service rep before printing. A helpful technique is to take
a Xerox of your image at full size and tape it onto the shirt to see how
it looks. If you determine that it needs to have an unusual placement then
send your 'mock-up' to the printer.
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You have the right expect minor deviation in the placement from shirt to
shirt. In some cases it is quite clear where the image is in relation to
the landmarks of the garment, (i.e.. the collar). In other cases, such as
a left chest the exact location can be more elusive. The printer will generally
load the shirt onto the platen the same way every time but even top quality
shirts can be quite irregular dimensionally and often the printer must make
a judgment call. If you have exceedingly specific criteria for placement
consistency you should make this clear from the outset.
Because the gamut for process printing on garments is much smaller than most
other printing methods you can not expect colors to match exactly. A carefully
engineered separation and a skilled inker should be able to deliver a pleasing
print that captures the essence of the range of tones and the levels of contrast
in the original, but will be unlikely to match it as well as an offset print.
Often touchplates are used to achieve colors that are out of range.
Process printing on dyed shirts yields a much narrower range than on white
shirts. If the result of this process looks even remotely like your original
you should be pleased. For spot printing the range of colors is similar to
offset. You should have no problem specifying colors from any of the standard
matching systems, including Pantone, Focoltone, and Trumatch. It also helps
if their ink department and print areas have a good graphic standard 5000k
light source to match colors under.
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Maintaining color consistency in halftone printing, especially process can
be a challenge for even the most seasoned printers. Hues in process printing
are determined by the proportional densities of the 4 process colors. These
proportions can be disrupted by any one of the many factors that determine
the amount of ink that flows through a particular screen. The most common
cause of color shifts from shirt to shirt within a run is uneven platens.
If the platens are not all level the critical off contact distance will change,
often causing a visible shift in the hues. Process colors can be difficult
to match from run to run if all of the critical variables are not recorded
and controlled by the printers. This is one of the reasons process printing
on t-shirts can be so ornery. The tools necessary to control this myriad
of interrelated parameters are not standard equipment in the vast majority
of screen print shops. The absence of tools such as deltascopes, colorimeters,
off contact gauges, and print pressure meters will indicate to the prospective
shirt buyer that the shop may not be capable of the consistency you see as
reasonable.
Hue consistency for spot colors from shirt to shirt within a run is not
ordinarily an issue, but color matching from run to run can be elusive if
the shop does not employ a structured color matching system. The presence
of a quality digital scale and a catalog of achievable ink colors will tell
you that a printer is capable if repeatable ink mixing.
This is an effect that is generally seen on shirts containing polyester.
Since the dyes used for garments don't readily bind themselves to polyester
fibers the shirt color can effect the printed area. This effect can be seen
immediately after curing or can appear weeks after the shirts have been
delivered. Red shirts with white ink are the most notorious for this effect
but may other combinations can be trouble.
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Scorching is caused by improper heating of the shirt between colors on press
in the flashing stage or in the main dryer during curing.Scorching can evidence
itself in a range of hues, from almost indetectable yellow to a Cajun blackened.
Plastisol inks are the most durable but require heat to cure. Large areas
of yellow or brown as well as brittle fibers are indications of a scortched
shirt. Printers must strike a delicate balance of temperature and time to
properly gel or cure the inks and if diligent measurements are not taken
shirts can be easily torched. Occasionally, this phenomenon can be caused
by sizing left in the shirts from the mill. Under normal curing conditions
this sizing can create a light, yellowish cast. There are several devices
that the printer can use to monitor these factors. For more details see the
next section.
One of the most carefully monitored factors in screen printing with plastsols
is the curing process. The ink must reach a certain temperature to completely
cure. Improper curing can be seen as inks that loose much of their vibrance
or opacity after washing. This should not be confused with fibrillation.
This is an effect that occurs on light shirts and is often confused with
improper curing. The effect is visible on prints that employ transparent
inks that use the whiteness of the shirt to achieve certain bright hues.
When these inks are washed the lack of a heavy plastic coating allows some
of the unprinted fibers to break through the ink layer and dull out or "frost"
the image. This predicament has recently become more of an issue because
shirt manufacturers have been driven by market forces to make heavier weight
shirts that feel smoother. The fibers in these super heavyweight garments
are the most susceptable to this effect. Process printing is the most vulnerable
to frosting as all of the inks used, except black, are transparent.
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The flexible nature of fabric can yield a distorted image if the shirts are
not loaded correctly. The adhesive that is used to hold the shirt on the
platen can catch part of the garment when it is being loaded and pull it
out of shape. There are loading techniques that can alleviate this effect
but certain shaped prints, such as hard geometric boxes, will show distortion
much more than others.
It is difficult to describe a specific benchmark for opacity. In halftone
printing it is especially problematic to balance dot gain and opacity
considerations. On light shirts you should not be able to see the weave pattern
of the shirt thorough the ink, even under minor stretching. On dark shirts
the problem is compounded by the need to cover the shirt color with a thick
enough layer of opaque lighter colors without making the shirt "bulletproof".
In most cases the level of acceptability is a judgement call, so you should
know poor coverage when you see it.
How well a shirt washes is determined by how well the inks are cured.
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The registration tolerances of the various presses used by screen printers
range wildly, but a well trained operator with decent well tuned equipment
should be able to make product with very little or no visible error. The
best way to achive a pleasing graphic image is to butt register the separations,
which requires nearly perfect registration to print sucessfully. Any gaps
between colors that are visible from more than a foot or two away are generally
beyond the level of acceptability.
This is term that describes the ammount of ink on a shirt. In certain printing
styles, such as athletic, a heavy deposit is acceptable and even, to a degree,
expected. In most other styles of printing any large ink area that stiffens
the fabric is objectionable. In extreme cases the weight of the ink can be
felt and the print will not breathe, causing a nasty adhesive effect on the
wearers chest on summer days. A decent printer will have developed a library
of techniques to achieve decent coverage and aviod having to donate the rejected
goods the local S.W.A.T. team.
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