Thursday, 6 October 2011

Elephant No. 4: Invisible Ink

For some reason, I've never tried invisible ink—not even as a child. I vaguely remember one of my brothers waving an invisible message in my face, then cackling and running away, but I never tried it myself.

Lemon juice is the simplest and most common form of invisible ink, revealed simply by holding the message over a 100-watt light bulb—and no, a compact fluorescent won't work. The heat of the bulb is what changes the composition of the lemon juice, essentially cooking the acids and sugars it contains.

There are four traditional types of invisible ink:
• Inks developed with heat, such as lemon juice, onion juice, milk, and vinegar
• Inks developed through chemical reaction, such as ammonia/red cabbage and corn starch/iodine
• Inks visible under UV light, such as sunscreen, laundry blueing, and tonic water
• Inks that disturb the surface of the paper—in other words, pretty much any liquid

Invisible ink can obviously be far more exotic than any of the examples above. Throughout history, however, the main criteria for invisible ink have been that the material used to write, and the means of developing the invisible ink, should be common enough that a field operative could both write and develop a message without special chemicals or equipment. That being said, I recently read an article about an invisible ink made with bacteria. Under certain a wavelength of light, fluorescent proteins—produced by seven specially engineered strains of E. coli—reveal colour-coded messages.

My first thought for today's elephant was that I should just use lemon juice. After yesterday's origami trauma, something simple would have been nice. However, once I started reading about invisible ink online, I decided on something more exotic: ammonia and red cabbage. When I mentioned this to my husband, he said he was very glad he was out of town today.

My reasoning was that I have an old bottle of ammonia in the house, and red cabbage is easy to come by. Also, a spy lurking about the Eastern Bloc during the Cold War would surely have been able to find both urine (which contains ammonia) and cabbage. Bonus: red cabbage can also be used to make a pH indicator. I could also have used vinegar instead of the ammonia; but, strangely, there was no white vinegar in the house. So, ammonia it is.


First of all, open the windows if you're using ammonia. Second of all, open the windows if you're boiling cabbage. According to the Wikipedia page I read, when any invisible ink dries, "the written surface should appear blank, with a similar texture and reflectivity as the surrounding surface." Okey dokey, then.

I found that trying to draw with ammonia using a toothpick or bamboo skewer is well-nigh impossible, as there is not enough liquid on the tip to see what you're drawing. So I tried a brush. A brush, however, holds too much liquid, making the lines fairly obvious, due to the rippling of the paper. I'm sure I should have used a pen nib, but I had no idea what ammonia would do to my precious art pens, so I used pointy skewers and a small paintbrush instead.

To reveal the invisible ink (in my case, not so invisible), you just brush the strained red cabbage liquid over the page, and voila!

Well, I suppose "voila" isn't exactly the right word. If you really squint, you can see the vague outline of an elephant. At first, when the paper was still damp, the image appeared only briefly, then began to disappear as the paper began to dry. I was deeply disappointed, thinking, "Clearly, when they say invisible, they mean invisible."

In my disappointment, I turned to lemon juice and a light bulb. Who in the world thought this was a good activity for kids? I ran the thing over 100-watt light bulbs, blasted it with a hair dryer, put it on top of the toaster, and eventually tried putting it inside the oven on low heat. The light bulb takes forever, and only develops the parts that are truly saturated with lemon juice. The hair dryer does nothing. Both the toaster and the oven mostly scorch the paper without making the design any more evident than it was before.

I began to think that I should ditch the whole idea of invisible ink and just start airing out the house. However, when gathering up the ammonia/cabbage drawings to toss in the recycling, I noticed that the design was actually developing and becoming clearer. Not that it's stunningly obvious, but at least there's something there now—as long as you look on the reverse, rather than the side on which you originally drew.

But now I'm wondering two things: were people supposed to read their messages backwards? And how long was an undercover operative supposed to keep a note written in ammonia ink, once he or she had laid on the cabbage juice? Hours? Days? It took at least four hours for my images to develop. If it was a matter of life and death, better write out your will. Just not in invisible ink.

Elephant Lore of the Day
I've always liked this well-known folktale, which originated in India. This is my own paraphrase, but there is a poem version of the story written in the nineteenth century by John Godfrey Saxe, and there are innumerable prose versions available, both in books and online. 

Six blind scholars were asked to describe what an elephant—an animal they had never seen—might look like.

The first, touching the elephant's side, suggested that an elephant must be very like a wall.
The second, touching a tusk, was sure that the elephant must look like a spear.
The third, grabbing the trunk, was sure that elephants must resemble snakes.
The fourth felt the elephant's leg, and thought that an elephant must be tall and strong like a tree.
The fifth, who touched only an ear, declared that an elephant must look like a fan.
And the sixth, seizing the elephant's tail, thought the creature must resemble rope.

So wildly did their opinions disagree, that they began fighting among themselves, eventually killing one another. 

To Support Elephant Welfare
World Wildlife Fund
World Society for the Protection of Animals
Elephant sanctuaries (this Wikipedia list allows you to click through to information on a number of sanctuaries around the world)
Performing Animal Welfare Society


  1. Now, on a day when you don't have time to do an actual elephant, but still want to post something... you could put up a blank piece of paper. Then, tell us you drew a beautifully detailed elephant in invisible ink, but didn't do the reveal.

    Honest, I did.