Thermochromic Secret Message

In this tutorial, I will show you how to create a "secret message" using thermochromic paint.

Step 1: Collect Your Materials

First off, collect all the materials you will use.

• Textile (I used an old tote bag)
• Thermochromic Paint ( Paint on Amazon)
• Conductive Thread ( Thread on Amazon)
• Fabric Medium ( Fabric Medium on Amazon)
• Stencil (I laser cut mine but feel free to draw it out)
• Cup (For mixing!)
• Brush (I used a watercolour brush)
• Arduino Uno (Don't forget the USB A to B)
• Breadboard (You can also use a Permaboard)
• Batteries (I used a 9V. Don't forget you need a way to connect it to your breadboard)
• 1 Diode (1N4001)
• 1 Transistor (TIP120)
• 1 Switch (For closing your circuit)
• Connector Wires (I use alligator clips and jumper wires)

Step 2: Create Your Stencil

I laser cut these stencils from an 11x17 sheet of cardstock. This will be used to paint on your design. You can also draw your design directly onto the textile.

Step 3: Paint Your Design

Mix your thermochromic powder with your fabric medium. Make sure you mix enough for your design. I used a plastic cup to mix the materials and applied the paint using a watercolor brush.

TIP: if you have stenciled your design, gently dab your brush onto the textile rather than painting on. Also, be aware of how much paint is on your brush. If you use too much paint, it will bleed and (possibly) ruin your design.

Step 4: Sew Your Message

This is where you will use your conductive thread. My stitches within the letters are tight in order to get an even distribution of heat. Sew all of the letters that you will want to disappear. In my case, I sewed everything but the words "SCREW IT"

TIP: When sewing, make sure you leave enough slack for connecting to your circuit.

Step 5: Connect Your Circuit

This step can get a little confusing! Follow the diagram above to connect your circuit. It should look a little like the pictures above. You don't have to use a 9V battery. I used it because it heated my elements much faster than two AA's would have. Be sure to add a switch so you can turn your message on and off! You can upload the code to Arduino that is attached in this step to get it turned on.

TIP: If you are having trouble uploading to the Arduino Uno, check your serial ports and make sure they are set to the appropriate port. If your ports are not appearing in Arduino try restarting the software. If it STILL does not work, try restarting your computer.

Step 6: Test It Out!

You have now made a secret message using thermochromic ink! Test it out!

TIP: If it doesn't seem to be working check your circuit. More often than not it is an error with the wires. If everything seems right, try a different battery!