It always amazes me how much we have still to learn about various types of media. The presentation by Lauren Buttle and Natasa Krsmanovic underscored how little we still know about watercolor pencils (also known as aquarelle or water soluble pencils).
Water color pencils first appeared during the 1920s, with Staedtler being the first to mention them in 1928. They are related to copy pencils, which contain a water soluble dye and were introduced in the late nineteenth century.
In their study, Lauren and Natasa and their coauthors, Laura Hashimoto, Michael Doutre, Kaslyne O’Connor and Rosaleen Hill, examined four products: Reeves watercolor pencils, Staedtler karat aquarelle 125, Staedtler ergosoft aquarelle, and Derwent watercolor pencils. These were first analyzed using mid-IR spectroscopy, which revealed that each of the products had the same general composition. All contained clay, water-soluble wax, a polysaccharide binder, and colorants. The wax was further revealed to be a modified polyethylene glycol, or mPEG.
The second phase of the project involved testing samples to determine the impact of conservation treatments and solvents. The researchers drew lines with watercolor pencils onto Windsor & Newton watercolor pen and ink paper that was subsequently cut into 14 sets of inch-long strips. They tested four colors – red, blue, grey, and black – for each product. Of 14 watercolor pencil test strips, seven were stored in the dark (that is, they were not aged), while seven were artificially aged at 95°C and 50% RH for 96 hours. They were then tested for reactivity with water, ethanol, acetone, and toluene immersion for 5 minutes each, non-contact exposure to 100% RH for an hour, and smudging with a smudge stick, with additional samples retained as controls. Color change was measured with a Minolta chromometer, with readings taken thrice for each testing area.
Their results showed that exposing watercolor pencils to wet treatments is exactly as problematic as one might assume. Aged and unaged samples both experienced significant bleeding when immersed, particularly undergoing aqueous immersion. Of all colors, red had the most dramatic response to immersion. Immersion treatments also resulted in color shifts, with polar solvents causing greater shifts in color than non-polar solvents. However, some of the color change was due to change in the color of the paper.
Humidification appeared to have no effect; however, the researchers did not dry the paper under pressure, and it is possible that there may have been some off-set of color if they had done so. All media was affected by mechanical smudging, although aged media was affected to a smaller degree.
This talk raised a lot of interesting questions, and the discussion following the presentation suggested avenues for further research. One attendee asked when mPEG was introduced, raising the idea that the composition of these pencils has likely changed over time, while others suggested testing the solubility of colors in xylene, or testing the pencil lead directly. This research will be continuing at Queens University, and I am excited to see where it will lead.
Author’s Note: The original version of this blogpost omitted the names of Michael Doutre and Kaslyne O’Connor. The author apologizes for the omission.
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AIC Blog Archives: Conservators Converse
Former Blog of the American Institute for Conservation