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).

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Iso Blue Wool

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 RReferences courtesy of TalasOnline.com, which calls them "Blue Scales"

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 RReferences 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."

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  • sophie
    How to read lightfastness blue wool scale?
    7 years ago

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