So after a brief return to typical West Coast mild weather, we woke up this morning to almost a foot of snow. Ugh, seriously? I’m beyond done with this ridiculous winter, but I have to admit the kids’ excitement makes up for it a little bit. They got up early, bundled up, and dashed out the door to make snowmen and slide down the neighbour’s driveway. A couple of hours later, they showed up on the doorstep, shivering and begging for hot chocolate. (Incidentally, this is how we discovered those waterproof pants I picked up for Tee last month are not very waterproof at all. Grrr.)
And this set the pattern for most of the day. Outside to play in the snow, inside to warm up, then back outside again. But when night fell, the kids were in to stay and I decided to keep the weekend fun going by introducing them to an activity I learned from my own mother: invisible ink!
Invisible ink is one of the simplest projects I know, but it kept the kids fascinated for over an hour creating secret messages and drawings for each other. All you need is lemon juice, a source of heat, and air. (If you don’t have lemon juice, scroll down for another option.)
Bottled lemon juice and a small paintbrush works great for this. If you don’t have the right size paint brush, a Q-tip will work in a pinch too. Once the lemon juice dries, nobody will be able to read the hidden message!
When it’s time to uncover the secret message, mom or dad can heat the paper just over the stove burner being very careful not to burn the paper. Watch as the secret message gradually appears!
I’ve used candles for this before, but I recommend the stove whenever possible. A candle flame is just too small and concentrated to heat the paper evenly, so you end up with little round scorch marks all over the page instead of an even brown.
What a neat way to pass on secret spy messages, create an old-timey treasure map, or even make a secret Valentine! Be aware the paper will be a bit brittle due to being heated, so handle with care.
If you don’t have lemon juice, this works with milk too!
How Does Invisible Ink Work?
The best activities teach as well as entertain. So for kids who are curious about the science behind this activity, tell them it’s all about oxidation. Lemon juice and milk both contain carbon compounds which are normally colourless, but when heat is applied, those compounds break down and release carbon. When that carbon is exposed to the air, it oxidizes and turns brown, revealing the secret message. Ta da!