This Year in Roman Technology: Invisible Ink and Other Delights

Got your attention? Haha. Who wouldn't want to know how to make invisible ink? And we finally figured it out this month!

This month, my Roman Technologists learned about writing, not literature, but the physical practice of writing. Different tools, different inks, different surfaces.  

We started by writing on papyrus. And I know you're thinking, "But that's not very Roman." My definition of Roman Technology in the context of this class is anything used, invented, or adapted by the ancient Romans. And they used papyrus quite a bit. We didn't make our own this time around. If you're interested in doing so, you should check out Dr. Dan Leon at the University of Illinois at Urbana-Champaign who grows his own papyrus plants and harvests for this purpose. I got to try it out with him this past summer at my NEH-sponsored K-12 teacher institute. It was FUN and smellier than I imagined. (If we can get our little RoTech garden rolling - more on this in a later post - we will definitely be trying out some native species to use in class projects.) 

We tried out three different inks that the Romans may have used.

1. SEPIA: Pliny the Elder mentions squid sac ink although not entirely related to writing, more for dyeing. Although smelly, it's easy to purchase since it's used in fancy dishes like pasta Nero, and it's easy to thin out with water and use with a reed pen. The kids enjoy this smelly activity.

2. ATRAMENTUM: The Romans used this ink, made from lamp black and gum arabic, most heavily. It's easy to replicate with a little carbon powder and water. Caligraphers still use this ink today, and I was amazed (and horrified) to see how it's made - surely the Romans would have used a similar method to produce this ink?

3. OAK GALL INK: This ink is endlessly entertaining to teach students about especially when the galls needed to produce the ink can be found by the students themselves on our school's campus. The students had so much fun foraging for these tree growths, caused by a tiny, harmless wasp, under the shady oak trees that populate our lunch picnic area. Sidenote: I'm really proud of an article I wrote about oak galls that was recently published by Science Friday. You can read it here. When one of my students found out about this article, he told me that he would go home and tell his parents he knew someone famous! LOL

In addition to different ink types, my students also tried writing on wax tablets, and for the first time ever, we tried out ink tablets, tiny wooden tablets written on with atramentum and bound by leather cord, like the ones found at Vindolanda. 

Last, I made tiny plaster walls for each of my students to try scratching graffiti into. I poured plaster into small disposable plastic saucers and then I painted them with colors common in Roman times: black and blue. After learning about Roman graffiti, the students assumed a Roman persona and then used Roman cursive letters to scratch some graffiti into their tiny walls. Partner students then interpreted the message as best they could. The kids mentioned this as their favorite writing surface!

My personal favorite was making invisible ink. I knew that it could be done. Philo of Byzantium, an ancient Greek engineer of the 3rd century BCE, used the chemical process behind producing oak gall ink to write secret messages. In his Compendium of Mechanics, he describes how when at war, “Letters are written on a felt hat on the skin after smashing gallnuts and steeping them in water. When they dry, letters become invisible, but if ‘flower of copper’ (or iron) is ground in water like black (ink) and a sponge is filled with water, when (the letters) are moistened with the sponge, they turn visible.” This kinda sounds like gobbledygook, but I know what he means. Step 1 - My students wrote on papyrus with a weak oak gall ink solution. Step 2 - They added ferrous sulfate (crushed iron) to water and mixed. Step 3 - After the invisible oak gall ink had dried on the papyrus, they dipped their fingers into the iron solution and rubbed it over the dried invisible ink. Step 4 - They were amazed when the chemical reaction between the tannic acid in the oak gall ink and the iron combined to turn the invisible ink a dark black color. Fun times!! You can see the magic in this YouTube video we made.

We'll be showcasing our invisible ink in a couple of upcoming outreach events. And I've been asked to appear at a Shakespeare Festival coming up in the spring. Oak gall ink was widely used across Europe and early America into the 1800s. In fact, it was the ink favored by Leonardo Da Vinci and the founders of our country who used it to write the Declaration of Independence.

Here are a few of the oak galls we harvested during our foraging session under the oaks at school. There were SO many different types. Jim Bentley, a teacher friend I met through the Grosvenor Teacher Fellowship (with National Geographic and Lindblad Expeditions) is cataloging and photographing the galls that his students find in the oaks at their school in California. He shoots multiple images over time, and he realized that the larva his students found was alive. As I was telling me students this story, one of my students said that he thought a wasp was emerging from a gall in was holding in his hand. He was right!!! We put the gall on my desk and let her slowly emerge. She was soooo tiny and cute. 

Our adventures continue as we head into a unit on ancient Roman food production. We'll be making ancient Roman bread, cheese, and trying out some herbs we've grown in our newly-built garden. More on that later. We've been super busy this month preparing for our outreach event centered on archaeology, Can You Dig It? More on that coming soon!