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Delta E: A Key to Understanding Lightfastness Readings

15 thoughts on “Delta E: A Key to Understanding Lightfastness Readings”

  1. I am absolute;y fascinated with information like this. I have been working with JND as a concept for a little while but you have added a completely new dimension. Thank you!

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    • You are SO welcome! We love that you find this information fascinating and valuable as clearly it is part of our passions as well.

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    • Great question. The measure would actually be the same since Delta E is neutral about how the change comes about and simply measures the difference in color between two readings. So, for example, when Cadmiums or Ultramarine Blue are exposed outdoors in an environment with moisture or humidity, chemical changes take place that are not really classic “lightfastness” issues, but which will cause an Ultramarine Blue to bleach out, or a Cadmium Red to get darker. Or we will see cases where a particular pigment will appear lighter after outdoor exposure, but due to chalking of the surface rather than fading, which is a form of erosion different from purely a fugitive color. Ultimately, however, while all of these changes can be described in terms of Delta E, that does not mean all of them are reflected in ASTM’s lightfastness rating even though they can impact how a pigment is used. So, for example, returning to our earlier example, while Ultramarine Blue and Cadmiums are all given a Lightfastness rating of I by ASTM, their use is restricted to indoor applications. As most paintings are exhibited and live their lives indoors few artists notice this, but for those who paint murals they will find them absent from our list of recommended colors for exterior applications. For more information on that aspect, the following are good links to look at:

      Exterior Mural Tech Sheet – Recommended COlors

      Selecting the Best Exterior Mural Pigments

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