Lightfast Testing: Water-Soluble vs. Non-Soluble

Lightfast test sheet on 12/23/21

As a sketchbook sketcher, I’m not as concerned with lightfastness as many artists are. If I learn that a product is especially fugitive, I might avoid it for general quality issues, but it’s not the first thing I consider (except on the rare occasions when I plan to sell or give away a piece). But if a product’s lightfastness concern keeps you from sketching, then that’s a good reason not to use that product (a philosophical issue more than a product quality issue).

Recently, however, a blog reader raised an interesting question about lightfastness. In the post in which I complained about several significant colors that were missing from Caran d’Ache’s Museum Aquarelle line, the reader mentioned that it may be because watercolor pencils generally have lower lightfast ratings (presumably compared to their non-soluble counterparts). Since I don’t pay much attention to individual ratings, this surprised me.

I’m sure someone has already done a lightfast comparison between watercolor pencils and their non-soluble counterparts, and I probably could find that information easily on the internet. But what’s the fun in that? I had never been motivated to conduct a lightfast test myself, but this question raised my geek antennae.

I wasn’t interested in testing all available colors in a particular line, since many other reviewers have already done that work (many thanks to them; it’s good data). Instead, I chose a small handful of hues that were common across both the water-soluble and non-soluble artist-quality lines and with a range of lightfast ratings. The contenders I chose are as follows: Caran d’Ache Museum Aquarelle vs. Caran d’Ache Luminance; Caran d’Ache Supracolor vs. Caran d’Ache Pablo; and Faber-Castell Albrecht Durer vs. Faber-Castell Polychromos.

Caran d'Ache's artist-quality line: water-soluble Museum Aquarelle (left) and non-soluble Luminance

Caran d'Ache's mid-level line: water-soluble Supracolor (left) and non-soluble Pablo

Faber-Castell's artist-quality line: water-soluble Albrecht Durer (left) and non-soluble Polychromos

Since it’s well known that some pigments are more fugitive than others, I wanted to match hue for hue by number. This was not as easy as I expected it to be for Caran d’Ache; a surprising number of colors are available only in one, two or three lines but not all four. It was easy for Faber-Castell because the two lines match perfectly.

For the water-soluble sets, I applied water to half the swatches to see if lightfastness is affected differently after they have been activated. My test sheet includes color numbers and, in parentheses, lightfast ratings found on each pencil’s barrel.

After scanning the image at the top of the post, I applied tape to half of each swatch. I have a southern-facing skylight that receives direct and indirect light almost all day. The test sheet was exposed beginning Dec. 23, 2021. Tune in for the results in a few months. 

10/29/23 It was brought to my attention that I never linked to my test results -- sorry about that! And I'm even sorrier that the test was a total bust. 

Taped and placed under the south-facing skylight.

Gratuitous eye candy.