A few weeks ago, we visited a local science museum and were given color changing pencils for completing a survey. The pencils blew my mind and I had to figure out how to make them myself. My brilliant cousin, who remembers everything and has a mind like a steel trap, instantly recalled Hypercolor t-shirts from the 90's and that was my launching point. After an intense Google session, I found the product and basic process I needed to start our color changing experimentation. With Easter right around the corner, eggs seemed the perfect presentation. Check out the details below.
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Thermochromism is when properties of a substance change color from a change in temperature. Leuco dyes are what make up the thermochromatic pigment we used to make our color changing eggs. You can read more about them at How Stuff Works: Thermochromic Ink. The pigment changes from color to a clear powder when you heat it to 92°F (33°C) or above. When you mix the pigment with a medium such as acrylic paint, you can see the color changing process. We experimented a few different ways.
For all of the experiments below (except where noted), we applied a base coat of acrylic paint to the eggs and then once dry, we added a coating or two of the pigment. We played around with the ratio of paint to pigment and generally we used 60/40 paint/pigment when using the clear glaze. We wanted some depth to the colors. You'll need to play around with the ratio when using colored acrylic paint for your pigment mixer. We list our conclusions below with best results listed first.
- By far, the purple thermochromatic pigment worked the best for body heat. Both with regular eggs and wooden eggs. The purple pigment was unique because instead of changing to clear, it changed to bright pink when heated. Very cool! It was not necessary to apply an acrylic paint base. We also used it for some disappearing ink fun - see Explore More for details.
- Then, we used a yellow acrylic paint base on a real egg. To make the pigment mix, we took the green thermochromatic pigment and mixed it with the same yellow paint we used for the base. The pigment color went from grass green to pea grean. This produced great results for the hot water method.
- We also used the yellow acrylic paint as a base on a wooden egg. To make the pigment mix this time, we used the green thermochromatic pigment and the thick clear glaze. This produced good results for the body heat method.
- We applied a light blue acrylic paint base on a real egg. We then used the blue thermochromatic pigment mixed with glitter acrylic paint. This produced a so-so response in the water and with body heat.
- Next, we applied the light blue acrylic paint base but on a wooden egg. We then used the blue thermochromatic pigment mixed with the thick clear glaze. Again, this was a so-so response. We concluded that the base paint color and pigment color were too similar to show perfect results.
- We rank the yellow thermochromatic pigment last for Mood Easter Eggs. We couldn't get a good coating applied of the yellow and because of the light color, all of our bases showed through. This produced beautiful mixed colors, but the dramatic color-changing just wasn't there.
NOTE: We highly recommend using a thick glaze when going with a clear coat mixer. A standard glaze just doesn't coat the egg well enough with the pigment. You would have to use multiple coats, and that would take forever to dry and the end color change would be less impactful.
On the look out for a new way to hunt eggs? Check out our LEGO Eggs post for details on how to mix building with hunting and extend the activity. Keep those kiddos busy longer!
We have so many ideas for using the thermochromatic pigments, but couldn't fit them all here. We couldn't stand not showing you this last one though. Check out what happens when we used a purple Sharpie marker to write a message on thick cloth, and then covered it with the purple thermochromatic pigment. The kiddos used the blow dryer to reveal the secret message.