Faber Castell Polychromos Pastels have been a go-to pastel for artists because they are individually rated for lightfastness, and provide a wide range of colors among the harder brands of soft pastels. Having a lightfastness rating does not mean that a color will never fade; it just means that the company is telling you the degree to which the color is lightfast, compared with other colors.
For these tests, I assumed that the earth colors and grays are about as lightfast as you can get, so I didn't test the entire line of Polychromos. Instead, I pulled out 74 colors from the full set that I thought would be most inclined to fade or shift color. The samples have been in my south-facing studio window in the northeastern US for at least a few hours a day for the past five years. The
samples were on the window sill, leaning downward against two to three layers of glass, rather than up toward the sun. The term "direct light" would be a bit of overstatement; there was some direct light and some indirect light. However, it was plenty of sun and time to alter some pastels significantly, and to give me an idea of which colors hold up best, and which would fade or shift before the others.
The top strips are the ones that were in my window, and the bottom halves were kept covered in a dark closet. The numbers correspond to the product number for each color, which was engraved on each stick. Here are the result images for all of the Polychromos sticks that I tested.
Overall, I was impressed with the way most of the set held up over time, compared with other brands I've tested. There are a lot of yellows, oranges, reds, and even a couple of violets, that by far exceeded my expectations. Those are colors that did poorly in some other brands. The bright greens also fared very well overall. The blues were disappointing, with more fading/shifting than anticipated.
I checked the results from time to time as the years went by, and removed the worst offenders from my set. But in this case, I am not going to interpret the results for you. It's pretty clear in the images what has changed, and by how much. You can decide for yourself what you want to keep, what you want to toss, or if you'd like to ignore my tests altogether.
The fact that some colors changed very little or not at all is not an indication that they would not change in the future. I interpret these tests in a more relative way, so that I can remove the colors from my palette that fade or change the fastest. Given our human life span, testing colors in indirect light is impractical, so I am relying on this accelerated version for information. Hanging work in indirect light, or with UV glass, does not insure that color will not fade; it will just take longer to do so.
Disclaimer: I am not a scientist, and your results may vary. I have done these tests for my own use and knowledge.
You can see my lightfastness test results for Charvin Water Soluble soft pastels here.
Click here to see all of my lightfastness tests.