Heat-Sensitive Colour-Changing Slime (without Thermochromic Pigment!)

Love making slime at home? This cool contact lens solution slime is made with a secret ingredient that causes it to change colours when it’s exposed to body heat—without the need for expensive thermochromic pigment!

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Ever since I came across this article on colour-changing slime, I’ve been meaning to try making it for my four-year-old. She loves to play with slime while her younger siblings are napping, and this seemed like such a cool variation on what we usually make!

Unfortunately, when I looked into buying thermochromic (or thermochromatic) pigment, all the options I found were so expensive that I couldn’t talk myself into buying it.

It may have been a question of bad timing, or perhaps that particular product just isn’t widely available where I live. But I simply couldn’t bring myself to spend such a large amount of money on something that would end up in the garbage after just a few weeks (or days) of play!

That’s why I was so thrilled when Elmer’s came out with a brand-new type of glue that has thermochromic pigment already built in—for a fraction of the cost!

I immediately purchased both colour combinations, and the resulting slime was a huge hit. So read on to find out just how easy it is to make this DIY colour-changing slime at home!

Note: This slime is not taste-safe. If your children are still young, you may want to try Psyllium Husk Slime or Edible Marshmallow Slime instead!

About Elmer’s Colour-Changing Glue

Elmer’s currently offers two types of colour-changing glue, so make sure you buy the right one if you want this project to work! (They’re both great, and I love the fact that both are washable and non-toxic.)

Sun-Activated Colour-Changing Glue

One type of Elmer’s glue changes colours when it’s exposed to sunlight. It won’t work for this recipe, but you can use it to make sun-activated colour-changing slime or even cool colour-changing window clings (click below for more details)!

Keep an eye out for the words “just add sunlight” on the bottle. This type of glue currently comes in two colour combinations: yellow/red and blue/purple.

Elmer's Sun-Activated Color-Changing Yellow-to-Red Glue

Heat-Activated Colour-Changing Glue

The other type of Elmer’s colour-changing glue changes colours when it’s exposed to heat. This is the kind of glue you’ll want to buy for this recipe. You’ll know you’ve found it if you see the words “changes color as you play” on the bottle!

At the moment, this type of glue also comes in two colour combinations: purple/pink and dark green/light green. You can buy both colour combinations by clicking the links below:

How to Make Heat-Sensitive Colour-Changing Slime

Required Ingredients

Here’s what you’ll need to make your very own colour-changing slime at home—without the need for expensive thermochromic pigment:

Note: The contact lens solution you use must list “boric acid” and “sodium borate” as ingredients in order for the chemical reaction to occur. We bought ours at Walmart and carefully compared ingredients and prices before choosing the brand pictured below.

Contact Lens Solution for Slime Containing Boric Acid and Sodium Borate

Alternatively, you could follow a recipe that calls for Liquid Starch and simply swap out the glue for the type mentioned in this recipe. Though personally, I prefer to use contact lens solution as a slime activator because it’s more widely available and less harsh on the skin!

Step-by-Step Instructions

1. Pour Glue into Bowl

Start by emptying an entire 5-oz container of Elmer’s colour-changing glue into a small mixing bowl.

2. Add Water

Add ¼ to ½ cup of water and stir to combine. The more water you add, the stretchier your slime will be—we added a full ½ cup. The water and glue didn’t combine perfectly (possibly because the water we used wasn’t warm enough), but the slime still turned out fine.

3. Add Baking Soda

Mix in ½ teaspoon of baking soda.

4. Add Contact Lens Solution

It’s time to add the slime activator! Start with 1 tablespoon of contact lens solution and stir until well combined.

You may notice the mixture starting to solidify a little, but 1 tablespoon likely won’t be enough to fully activate your slime. You’ll probably end up needing somewhere between 1 tablespoon and 1 ½ tablespoons.

Once I’ve added the initial tablespoon, I usually add one small squirt at a time, mixing well between each addition. Don’t add too much at a time or your slime will become rubbery! (You can fix this by adding warm water and gently working it in with your hands, but it’s much simpler to prevent this issue altogether by adding the activator slowly.)

I usually stop adding contact lens solution when the mixture stops behaving like a liquid and starts sticking to the sides of the bowl, as pictured below.

5. Knead Slime

Once you’ve added enough activator, it’s time to knead! The slime might be very sticky initially, but the more you knead the slime, the less sticky it should become. Don’t be surprised if it takes a lot of kneading!

Note: If you like to wear rings, please remove them before kneading the slime. I forgot to remove my wedding ring a few times while making slime with my four-year-old, and some of the mixture found its way into a crevice on the underside of the ring and caused a rash on my finger. I had to soak the ring in isopropyl alcohol before I could start wearing it again, and it took quite a while for the rash to fully disappear.

If ever your slime is simply too sticky to knead, you can always add a little bit of extra contact lens solution to your hands to make things easier. Once the slime stops sticking to your hands, it’s ready to play with!

How to Play with Heat-Sensitive Colour-Changing Slime

The reason this slime is so cool is that it changes colours when it’s exposed to heat—including body heat. This means that it will actually change colours while your child plays with it as the warmth from their hands changes the temperature of the slime!

But what do you do if the ambient temperature is already high enough to trigger the colour change?

We chose to use the purple-to-pink glue, which is ordinarily purple, but turns pink when it’s exposed to heat. And sure enough, when it was kept at room temperature, it stayed pink, which meant that manipulating it with warm hands didn’t bring about any changes.

Thankfully, there’s a very simple solution: just store your slime in the fridge when it’s not in use!

At room temperature, our slime remained pink. But this is what happened when it was placed in the fridge for a little while:

Purple to Pink Color-Changing Slime Transformation

So in order to take full advantage of the slime’s colour-changing capabilities, all you need to do is simply place it in the fridge in a sealed container when not in use, and take it out when your child is ready to play with it. The warmth of their hands will take care of the rest!

Once the colour transformation is complete, you can even extend the fun by placing cold objects on your slime (for instance, a spoon that has been kept in the freezer) and watching as they leave a darker imprint by bringing the temperature of the slime back down!

Note: Slime that has been stored in the fridge is a little stiffer than normal, but it quickly becomes stretchy again when it’s played with. For best results, store it in the fridge when not in use, but leave it out at room temperature for about 10 minutes before your child starts playing with it.

Related Slime Articles

Can’t get enough of homemade slime? Check out this cool recipe that also uses contact lens solution:

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