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How to Make Color-Changing Thermochromic Slime

After having obtained a degree in biochemistry, Leah works for a small biotechnology company and enjoys writing about science.

This Slime Changes Color!

This slime used a black/pink color changing pigment and would shift color at 88F (31C).

This slime used a black/pink color changing pigment and would shift color at 88F (31C).

Simple STEM Activity with Thermochromic Pigment

Creating a slime that changes color with temperature is an easy STEM project for the home or classroom. The addition of heat-sensitive pigments (thermochromic pigments) causes the color of the slime to shift at a specific temperature. Depending on the thermochromic pigment added, the color may shift at different temperatures. Pigments that shift at 88°F (31°C) or 77°C (25°C) are recommended for this project, as some pigments require temperatures above 90°F (32°C) to shift. It is difficult to obtain the higher temperatures in a classroom setting.

Mixing the Thermochromic Pigment Powder

Thermochromic pigment powder is extremely light and will spread easily. Take care when mixing it into the glue base used for slime!

Thermochromic pigment powder is extremely light and will spread easily. Take care when mixing it into the glue base used for slime!

Materials Required to Make Color Changing Slime with Borax

  1. 1 oz. white school glue (about ¼ bottle)
  2. 3 tablespoons of water
  3. ¼ teaspoon borax mixed into 2 tablespoons of water.
  4. 3 teaspoons thermochromic pigment
  5. Food coloring (optional, useful for thermochromic pigments that shift to a colorless state)

Materials Required to Make Color Changing Slime without Borax

  1. 1 oz. white school glue (about ¼ bottle)
  2. 1/8 teaspoon baking soda
  3. 3 teaspoons thermochromic pigment
  4. Bottle of saline-based contact lens solution
  5. Food coloring (optional, useful for thermochromic pigments that shift to a colorless state)

Instructions for Mixing Thermochromic Slime

Before mixing the slime ingredients, verify the activity of the thermochromic pigment. Heat or cool the pigment to the temperature at which it shifts, verifying the pigment is active prior to using it in the recipe.

If using food coloring for slimes which transform to a colorless state, make sure your color is the opposite of the pigment color. If a red food coloring is used with a red pigment, you will not be able to see the shift when the slime becomes colorless. For a red pigment, select a yellow food coloring that will not overwhelm the pigment in the recipe.

Thermochromic pigment is supplied in a powder form. Take care when using the powder as it spreads easily and may stain. Do not expose the thermochromic powder to sunlight for an extended period of time, as this may degrade the molecular structure of the pigment and cause it to lose its color-shifting capabilities.

For the recipe including borax, the instructions are:

  1. Add 1 oz. white glue to a mixing bowl.
  2. Add 3 tablespoons of water to the mixing bowl and stir.
  3. If desired, add a few drops of food coloring.
  4. Add 3 teaspoons of thermochromic pigment to the mixing bowl and stir to combine.
  5. Mix the 1/4 teaspoon borax with 2 tablespoons of water in a separate bowl or cup.
  6. Add the borax solution to the glue/pigment solution and stir until it begins to combine.
  7. Knead the slime until it becomes cohesive and is no longer sticky.

For the recipe without borax, the instructions are:

  1. Add 1 oz. white glue to a mixing bowl.
  2. Add 1/8 teaspoon baking soda tothe mixing bowl and stir.
  3. If desired, add a few drops of food coloring.
  4. Add 3 teaspoons of thermochromic pigment to the mixing bowl and stir to combine.
  5. Add 1 teaspoon of contact lens solution and stir until it begins to combine.
  6. Knead the slime until it becomes cohesive and is no longer sticky. If the slime remains sticky, add contact lens solution until it is smooth and does not stick to your hands.

The Color is Dependent on Temperature

On a hot day, the pink/black thermochromic slime will turn a pink color. When the temperature cools, it will shift back to black. Experiment with friction, body heat, and ice cubes to change the color of the slime!

On a hot day, the pink/black thermochromic slime will turn a pink color. When the temperature cools, it will shift back to black. Experiment with friction, body heat, and ice cubes to change the color of the slime!

Change the Color of the Slime!

Once the slime is completed, get your slime to change color by applying heat. On a hot day, the slimes which change color at 77°C (25°C) will be in the shifted state. Using an ice cube will cause the color to shift to the original state. The pigments that shift at 88°F (31°C) will require a heat source to shift unless the day is very warm. Try placing the slime on a hot playground slide or on a cookie sheet heated by the sun! Friction will also cause the slime to change color, so rolling some of the slime in your hands will cause it to shift. The color change is reversible, so you can continually heat and cool the material to watch the color change many times.

how-to-make-color-changing-thermochromic-slime

Why Does the Slime Change Color with Heat?

Thermochromic pigments contain a molecular structure that changes at a specific temperature, which alters the wavelengths of light it reflects. For the black changing to pink pigment, the pigment will absorb all light wavelengths until it reaches 88°F (31°C). At the higher temperature, the molecular structure shifts and absorbs all wavelengths but red/pink, which is the longest wavelength on the visible color spectrum. The reflected red/pink color is what our eyes observe when this shift happens. A pigment that shifts from blue to colorless goes from reflecting only the blue wavelength to reflecting all of the wavelengths.

The capabilities of thermochromic pigments are used for simple thermometers. Another application of thermochromic pigments is in heat-sensitive paper, which allows receipts to be printed without the use of ink.

Change the Color of Thermochromic Slime Using Ice

Other Applications of Thermochromic Pigment

Heat sensitive pigment may be used in other projects, such as

  • Color-changing playdough. Use your favorite playdough recipe and add thermochromic pigment after the cooking stage for color changing fun!
  • Thermocolor Paint. Use a transparent gloss medium as a base and add the thermochromic pigment. Combine thoroughly and use the paint on a mug to watch a color transformation when hot liquid is added.
  • Color changing thermometer. Create thermocolor paints from pigments that shift at different temperatures. Paint a strip of each thermocolor paint on a white surface and label each one with the temperature where the color-shift occurs. Place the thermometer in a location that does not receive direct sunlight and observe the outdoor temperature by which pigments have changed color!

Questions & Answers

Question: Can you add the food coloring after the slime is made (the thermochromic pigment is well worked in)?

Answer: Yes, you can add the food coloring after the slime is made. It might be harder to work the food coloring into the slime once it is already made, but you may certainly add the colorant after making the slime.

Question: Can you give me fun facts about slime?

Answer: 1) Slime is a non-Newtonian liquid, which means it behaves like a liquid and a solid at the same time.

2) Mayonnaise will remove slime that gets stuck in hair.

3) The television show "Double Dare" doused contestants in slime when they answered a question incorrectly.

Question: Is it ok to handle the pigment frequently in the slime?

Answer: The pigment is safe to handle, but should not be heated above the recommended maximum temperature in the instructions for use (this was well above 200 degrees Fahrenheit for the pigment used in the slime manufactured for this article). As with all homemade slime, care should be taken to wash hands after use as borax can be a skin irritant.

Question: Where did you buy your color-changing pigment from?

Answer: I bought my thermochromic pigment from amazon, as it was easiest to source online.

Question: How much time will it take to make color-changing thermochromic slime?

Answer: It takes about 10 minutes to make color-changing slime. Most of this time is mixing the ingredients and adjusting the amount of fluid with borax/contact lens solution until the slime is no longer "sticky."

Comments

Leah Lefler (author) from Western New York on May 18, 2018:

Adria, you are correct! I corrected the error (thank you for pointing that out)! I also added a wavelength chart to the article.

Adrià on May 18, 2018:

I liked the experiment but red wavelenght is the largest, not the smallest i think

Leah Lefler (author) from Western New York on April 29, 2018:

Hi Shawna, I made one batch with about six kids in my Maker Camp. We divided up the slime into zip lock baggies for them to take home. It could be divided among 10 kids per batch (with each child taking home a smaller amount), so I would at least increase the recipe by 10. You will only need one container of thermochromic pigment - it goes a long way. I used 3 teaspoons from my container and it appeared there was enough left to make another 10 batches. You will need considerably more glue and borax, but fortunately glue is the inexpensive part of slime!

Shawna on April 29, 2018:

How much slime does this make? I would like to do this with about 100 students and I'm trying to figure out how much to buy.

Leah Lefler (author) from Western New York on February 06, 2018:

It is extremely fun to make, Shane. We have had a lot of fun making color-changing slime and experimenting with using different thermochromic pigments to create a slime thermometer! Let me know how your experiment goes!

shane on February 06, 2018:

this project is so awesome i am totaly doing this for my stem fair project.

Leah Lefler (author) from Western New York on October 30, 2017:

Thank you for the offer, Eva - I don't do reviews for payment from a company or receipt of product, but your thermochromic pigment does work extremely well. A little goes a long way - I am donating some pigment to our school so they can perform a few science experiments in their new STEM project area.

Eva on October 30, 2017:

Leah,

Thank you so much for sharing your experience with our Color Changing Thermochromic Pigment. We're so happy you like it. If you leave us a 5 Stars Product Review on Amazon, we would love to mail you another 10 grams Thermochromic Pigment for FREE. It applies to all your readers too. We love our customers.

Eva

Atlanta Chemical Engineering LLC

Leah Lefler (author) from Western New York on August 04, 2017:

It is a great deal of fun, Karen! I recently did this recipe with our local Maker Camp and the kids really enjoyed it. They would put it on the warm playground slides to cause the color to shift to pink, then use ice cubes to "draw" on the slime to change it back to black. They had a great time!

Karen Hellier from Georgia on August 03, 2017:

Such a wonderful and very detailed hub. I wish I had this recipe when I was doing home daycare!

Leah Lefler (author) from Western New York on August 02, 2017:

I didn't have anything like this as a child, either, Peggy! I love exploring science with kids, and I hope it inspires them to pursue careers in one of the STEM fields!

Peggy Woods on August 02, 2017:

What a fun project for kids! We did not have anything like that when I was a child. I have to admit it was a long time ago! Haha!

Leah Lefler (author) from Western New York on August 01, 2017:

It is one of the best slime recipes we have done so far, S Maree! I have found the borax slime has the best consistency, but the contact lens version also works well. The viscosity is about the same for both formulations. The thermochromic pigments can be obtained online - there are different versions available. Some change from one color to another color, while others change from one color to clear (colorless).

S Maree on August 01, 2017:

Jee-mi-nee! Why didn't we have such cool experiments in school?

Can you show us how the different formulas behave? Is the viscosity the same? This enquiring mind wants to know!

How are the thermochromic pigments obtained? You've got this geezer's attention! Good work!