On alphabet posters and flashcards, the short I sound is often accompanied by an image of an ink bottle. We decided to add in an extra short I sound, and make our upper and lowercase letters from invisible ink.
Kids are fascinated by the concept of something being present but unable to be seen. About a year ago I was in my bathroom getting ready for the day with Petal wandering in and out as 1 year olds do. A few minutes later, Blossom and Bud came in and declared “We’d like to be made invisible.” “That could be fun,” I replied, thinking they were in the middle of some imaginary adventure. But Blossom continued in earnest sincerity “There’s a bottle of invisible power in the lounge room.” I continued to play along, but was a little puzzled as to what was really going on in her head, till she ran off and returned with …
Petal had just reached the stage of being able to abscond with things from my vanity top. Not only did the label say ‘Invisible’, I was informed, but the picture showed clothes being worn by invisible people! Roll it on us please Mum. LOL.
In my early days of science teaching, I taught an introductory chemistry unit around the theme of a party. One of our first tasks was to prepare party invitations, using invisible ink. I have a collection of chemical recipes for varying inks and their revealing agents, but obviously for a home preschool program, we need regular household substances.
There are a number of liquids you can use and a couple of methods for uncovering the secret message. We chose to experiment with lemon juice, bicarb soda solution and milk.
We used cotton buds to apply each ‘ink’ to the paper. First, Bud wrote upper and lowercase letter I’s in each of the three liquids. I labelled each page with the medium we’d used so we could evaluate their effectiveness once the experiment was complete.
I then gave Bud three more labelled pieces of paper for him to draw an image of his choosing using each of the liquids. He wrote his name with one, drew a self-portrait with another and wrote a recently learned letter with the third.
Once each of the pages had dried, there was some evidence of liquid damage, but essentially they looked like the blank pieces of paper we’d started out with. So now for the magic reappearing act.
The first method for revealing the hidden messages is to apply heat. The theory is that the lemon juice, bicarb and milk all contain chemicals which weaken the paper and so when heated, these areas of the page oxidise more readily and produce a darkened image. In the science lab, we used Bunsen burners. At home, we started with a light bulb, as demonstrated on EXPLORABLE. I tried applying a hot iron. We attempted a hairdryer, as recommended by Tinkerlab. All to no avail. I suspect that the bottled lemon juice we tested was not as strong as the fresh lemon juice used in these experiments. So we resorted to using a candle flame.
Here’s the light image revealed from the lemon juice ink.
To my surprise, milk ‘ink’ gave the clearest ‘burnt’ image. In fact, it appeared so readily, it’s possible it would have become visible with a less aggressive heat source so you may like to try a light bulb first after all.
The next method for exposing the invisible image is to paint it with an indicator. Lemon juice and milk are both acidic while sodium bicarbonate solution is alkali. All should produce a colour change when brushed with indicator. I would have loved to have used red cabbage indicator again, as we did in our first A is for acid experiment, but there was no red cabbage at the supermarket I visited this week. Grape juice concentrate can apparently be used to achieve a similar result. We went with grape juice, and I must say the results were rather underwhelming.
Here’s the test page I did for the grape juice reveal, using all three liquids. While it was possible to discern the hidden image while the page was wet, no lasting colour change occurred and there was minimal difference between the acid and alkali tests.
In conclusion, invisible inks has been a great experiment. And our recommendation for the short I page in your scrapbook would be to paint your letters with milk and use a candle flame to make them reappear. And if you have success with this, who knows what pictures of invisible castles might start gracing the blank pages in your household!!
Coming up this week
The short I sound will continue to steer us on a science course this week with ink chromatography and learning about insects on our to-do list. We’ll also attempt to improve our social skills by role-playing introductions.