Make Valentine's Day Cards with Invisible Ink

Did you make invisible ink when you were a kid? Maybe you used it to write hidden messages to your best friend, or you composed secret notes and left them lying around just to see if someone would discover the mystery.

If you worked with invisible ink, you probably used lemon juice or vinegar to reveal a message written with baking soda and water. Well, there’s another method that makes invisible ink pop with color once it’s un-invisible, and that’s turmeric mixed with hand sanitizer.

Turmeric is a traditional spice found in Asia and used in a lot of Asian cooking. Whenever I make chicken curry, I’ll add a dash of turmeric. It’s a terrific spice that you should have on hand, as it has some great anti-inflammatory properties and a good flavor too. (Seriously, I often sprinkle turmeric on my popcorn, along with a generous helping of salt and butter.) It’s also good for adding rich yellow coloring to a dish.

But back to the invisible ink. This would be a fun project to do with your kids for Valentine’s Day! They can make secret messages on Valentine’s Day cards for siblings, parents, or friends, and then use the turmeric concoction to reveal the hidden note.

Here’s how to do this!

Supplies You’ll Need for Invisible Ink

Baking soda
Water
Hand sanitizer
Ground Turmeric
White paper (thicker paper like cardstock works well but any paper will do)
2 Paint brushes
2 small bowls
Optional: paper towels or a towel to lay down under the paper.

Directions for the Invisible Ink Project:

1. Gather all the supplies needed.

2. In a small bowl add 1 tsp baking soda and 1 tsp water, mix well, and set aside.

3. Use a paintbrush and write a message on the piece of paper using the baking soda/water mixture, then set it aside and allow it to dry.

4. In another small bowl add 3 squirts of hand sanitizer and 1-2 tsp of turmeric. Using the second paintbrush, stir the hand sanitizer and turmeric together.

5. Paint over the message with the turmeric mixture to reveal the message!

*Use caution with turmeric as it can stain surfaces.

So, why does this happen? You might want to explain the science behind this neat effect to your kids. When you paint with the turmeric and hand sanitizer mixture over the dried baking soda message, the turmeric exposes the pH level of the baking soda, causing it to develop a deep red/yellow.

Another Science Project with Turmeric

You might want to expand this fun activity by testing out the pH level of other household liquids, such as lemon juice, vinegar, soapy water, watered-down shampoo, milk, etc. You would simply mix turmeric powder with water to create a paste and then use a dropper or paint brush to add small amounts of those different household liquids, each in a separate dish.

As you observe the color change in each solution, you can note which liquids are acidic, as they would look yellow, and which are basic, as they would develop a reddish hue.