I like making cryptograms and treasure hunts for people. With a little skill, it is possible to make a treasure map that looks like some long dead pirate scrawled it into existence.
This had led me to make my own inks, and in that process, I discovered some science experiments that you and/or your children might want to try.
This year, after having some success with making ink by boiling tree bark, I discovered the wonders of knotweed. In the spring, I collected some of the new red leaves, chopped them up and boiled them in my craft pot.
Then I removed the leaves and bottled up the pink red liquid. I assumed this ink would make nice bright red letters, and it did, until the letters turned green, which was about three minutes after I started writing the letters.
A happy accident revealed another startling color change seen with this ink. I decided to cook the red ink down some more, to make it thicker. I dumped some of it into a cast iron skillet — one that I only use for craft projects. The red ink quickly turned black.
Having no knowledge of chemistry, but wanting to understand more, I contacted Dr. Willem Leenstra, Emeritus Professor of Physical Chemistry & Spectroscopy at the University of Vermont, and asked him what he could tell me about my pink to green ink. While he could not explain the specific chemical reactions, he assured me that these types of reactions are not rare.
“The phenomenon of stark color changes in materials upon changing the water content is not uncommon,” he said. “Two percent cobalt chloride (CoCl2) is an inorganic dye. In its active form (dry) its color is blue, but when … water-saturated it turns pink.”
According to Dr. Leenstra, there are also other molecular mechanisms that affect the color of an ink or dye. “There are pH indicators (usually organic dyes) that exhibit severe color changes with changes in pH. You can even buy pH indicator strips in pet stores because the acidity of aquarium water is critical to fish.” Jason Alden, who teaches drawing at the Brattleboro Drawing Studio, said that even though the green ink I made was lovely, its beauty might not last. “‘Color fastness’ is the term we use to describe whether an ink will keep its hue after years of being exposed to sunlight,” he said. “You have to test these inks.”
This of course was music to my science-loving ears. I did a little research and discovered that eight months of exposure to direct sunlight is a common test of an ink’s color fastness. I also learned that vinegar is a common ingredient added to inks, to help them resist changes caused by sunlight.
I mixed up a new batch of ink, added vinegar to it, and painted words onto some paper. I then covered over half of each message with a paper strip. I taped the test sheets up against a sunny windowpane.
Sadly, what I can tell you now, is that my lovely green (from red ink) fades to brown in a few months’ time. It is not remotely the same color now as the wonderful green ink I made and is not colorfast.
If you would like to explore making inks with your child this summer, check out the book “Make Ink: A Forager’s Guide to Natural Inkmaking” by Jason Logan. It is a friendly and inspiring invitation to experiment and learn.
Is there a topic you would like Rolf Parker to consider for a Full STEAM Ahead column? Let him know via email to firstname.lastname@example.org. He has a master’s of science degree in en-tomology from Clemson University and taught math at Landmark College and Hilltop Montessori School. He has been a professional math, science and writing tutor for more than 15 years, and lives in Brattleboro with his wife and 10-year-old boy. Visit his webpage at books-fromvermont.com.