Digital Prints

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Mastering Digital Printing
Visual vs. Measurement Testing
The simplest way to test print deterioration is to run different samples under one test and
then look at the samples and visually compare them with a control set that wasn’t exposed
to the test conditions. For a lightfastness test, the controls are either covered up next to the
test samples, or they’re stored in the dark nearby. Visual tests are usually run by individual
artists because they’re relatively easy to do. Just line up the samples and visually decide which
you like best, or in the case of a lightfastness test, which appear to have faded the least.
Most testing labs and serious testers, however, run instrument-measured tests (using either
a spectrophotometer, colorimeter, or densitometer). Printed color samples are measured
before, during, and after the test is complete. The test ends either when a stated period of
time has elapsed, a certain amount of irradiance (exposure) has accumulated, or a specified
densitometric endpoint value is reached (see “What Are Endpoints”). The measurement
values are then computed or graphed for analysis (see Figure 5.4).
Dark Fading Tests
The fading of prints occurs under two main types of unrelated conditions: dark storage
and light display. Dark fading (also called “thermal image degradationÆ or “dark aging”)
is usually the result of the inherent instability of the colorants and the media, or because
of the effect of other influences such as heat, humidity, and environmental contaminants.
Dark fading can be exacerbated by high temperatures and/or humidity, and this type of
test is frequently conducted in high-temperature ovens or “accelerated aging chambers”
using the Arrhenius test method.
Figure 5.4 A graph of fade resistance
for eight lithographic inks using total
color change expressed in ∆E (Delta-E)
units.
Courtesy of Q-Panel Lab Products