Tuesday, February 26, 2013

Tech Talk: Pigments - Week 6



Lightfastness Test Strips
(bottom half is the sun-exposed section)

Back in January, I painted these test strips of Mission Gold watercolors because I was concerned about the lightfastness of the pigments used in manufacturing these paints.  As I've reported before, I cut the sheet down the center and put half in a drawer in my flat files and half on an enclosed porch that gets a few hours of strong sun on clear days.  Despite the limited sun exposure during our rainy winter months, there are definite changes to many of these pigments.

The sun-exposed yellow has become darker in the full-strength strip, but other colors have either become slightly dull or are changing color slightly.  At full strength, permanent rose, permanent violet, and burnt sienna are faded and somewhat duller now and prussian blue is slightly faded and also leaning towards green. 

Changes are more noticeable in the tints, which is often the case with impermanent pigments.  While orange and peacock blue had only slight fading, there is noticeable fading to the permanent rose, rose madder, permanent violet, prussian blue, and burnt sienna.  Sap green and Van Dyke brown both showed moderate fading. 

Out of curiosity, I changed the white background of my photo to a 60% grey tone in Photoshop.  The neutral grey really makes the colors pop and makes it easier to see the changes to the sun-exposed pigments.




I'll be leaving the test section in place on the porch for the forseeable future.  Even with many hours of full sunlight, it can take several months to see the full extent of changes to pigments.  I plan to report back here in a month.

7 comments:

  1. Chris, thanks so much for this post and for your experiment. This is valuable information! Perhaps you should direct the manufacturer of these paints to your blog post :-)

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    1. Thanks, Kathy -- when I received the free samples of this paint, I contacted the distributor with my concerns, but they have not been interested in discussing it. I will definitely share the results of this experiment when I have a bit more data. Unfortunately, in the meanwhile, they are funding major merchandise awards (thousands of dollars per event) at many big watercolor shows.

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  2. I'm surprised that every color looks affected by the light exposure to me when I enlarge your photo! I was never aware that a color could become darker and duller but always thought they just faded to a paler version of the original! Interesting!

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    1. I've been careful not to base my observations on the photos, just on the actual test strips, because I can't be sure the photo process and posting online aren't affecting the appearance. But I agree that there are definite changes to many of the colors. And yes, it seems counter-intuitive that light would make colors darker. For some reason, yellow is at risk there -- aureolin has been rumored for a long time to darken with light exposure and Hilary Page says her tests showed that problem with it.

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    2. I should specify that the yellow in this test is not aureolin, but other yellows share this problem.

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  3. Wow Chris...there is quite a difference there. I'll not be buying this brand! Thanks for going through with the testing!

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    1. We artists can't be too careful with our materials -- we put so much time into our works that it would be heart-breaking to have them fade quickly. I learned this lesson the hard way in college when we painted with liquid dyes -- every one of my paintings turned to mush grays after only a few months exposed to normal indoor light.

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