Digital Prints

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Mastering Digital Printing
Since D4303 is a complex standard that requires instrument measurements, the ASTM
has also developed two simpler ones. Standard D5383 describes a method for exposing
color samples indoors to sunlight coming through a closed window. Three to five outside
observers then rate each sample by comparing it to a Blue Wool Reference (see next
section) that shows the same amount of color change. Standard D5398 is similar and even
simpler since it doesn’t require outside observers, and it can be used by any artist to evaluate
the lightfastness of his or her own materials.
How will these new ASTM standards affect the world of digital printing? Because they are
an all-volunteer organization and not really in the business of testing themselves, ASTM
is hoping that the major manufacturers start doing their own tests based on the ASTM
standards, which, importantly, make no predictions of print-service life.
Blue Wool Lightfastness Standard References
The Blue Wool Lightfastness References were, and still are, aimed at those who work in the textile industry. The European version is part of the ISO
standards, and it gets its name from the dyed blue wool fabric bands or swatches that are used to visually compare fading rates. Much like a litmus
test, Blue Wools act as a visual reference or “dosimeter” for users like museums to determine when too much light has fallen on an artwork so it can
be removed from display. Blue Wools also are used as a timing device for knowing when to end a lightfastness test (although they have become less
important or needed with the introduction of accurate testing instruments that can control exposure times and intensity). There are eight levels or
references, with #8 being essentially permanent and #1 being fugitive (each is roughly twice as light-resistant as the one before) (see Figure 5.7).
Figure 5.7 ISO Blue Wool references
after an actual 10-week south-window
test. Left is before the test; right is
after. Test sample is half-covered to
keep those references from being
exposed to light.
Blue Wool References courtesy of
TalasOnline.com, which calls them
“Blue Scales”
In the U.S., the Blue Wool References are manufactured differently, but because they are more difficult to use, many U.S. printmakers use the
European ISO ones.
The Blue Wool References are not just for sheep shearers and textile dyers. As a simple, comparative reference, digital printmakers, especially
European ones, are now also using Blue Wools to indicate in general terms how permanent a print is or could be. For example, British artist and
giclée printmaker Colin Ruffell refers to his large-format prints achieving “a Blue Wool 6 rating, which is the minimum lightfastness requirement
to meet the British and international standards set by The Fine Art Trade Guild in the UK for limited edition prints.”