The Ann Arbor Book Fest was held in the main library. I talked to bunches of bookstores, artists, other author, etc, and watched some demonstrations of making medieval dyes for calligraphy.

The demos were done by my friend Randy Asplund .

When I first met him, back in the late '70s, he did paintings of knights and dragons and such using acrylics and oil paints.

Now he does calligraphy and illuminated manuscripts on vellum he makes himself using inks and dyes that he also makes himself, using the medieval techniques.

He did a demo of making a green dye/paint from buckthorn berries. This is a multi-step process that starts a lot like how I made the buckthorn berry juice last fall, but does not include tasting it.

Buckthorns are a powerful laxative, and eating them does not create a green dye suitable for artwork.

What I didn't realize is that buckthorn juice is a pH indicator. Its dark purple (and quite acidic - pH 2.5) when you extract it from the berry, and turns yellow/green when the pH is increased.

Making a pH indicator from red-cabbage is a common kitchen-chemistry experiment for kids. I just never thought about using buckthorns.

A little time on the web revealed that a number of berries have anthocyanin compounds that turn color depending on the pH. And once they've changed color, they are color-fast and even sunlight resistant.

I got my degree in chemistry from SUNY Environmental Science and Forestry. The chem department put some effort into finding lab experiments related to trees and nature, since that was the school's focus.

I've got no idea how the profs missed the idea of smushing blueberries (or too damn many buckthorns), and determining the pH ranges where the color changes occurred.