Yarka pastels?

[Kitty Wallis]

..."make sample swatches on a suitable surface, cover half of each swatch, and leave the other half exposed, and set the panels in a window facing the sun. Check them once a week, comparing the covered half with the exposed half."

Thank you Virgil,
I appreciate your comment on my paper. I plan to test my pastels as you suggested above.

I did such a test with the usual brands and colors of tinted pastel paper. Within a few months most of them were faded by more than half. I used the back shelf of my car.

Kitty