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How to Make Color Changing Thermochromic Slime

Updated on August 1, 2017

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). | Source

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! | Source

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)

Low Temperature Color Changing Pigment

Low Temperature Cold Activated Thermochromic Bi-Color Pigment Pink changing to Black at 64F/18C Perfect for Color Changing Slime Silly Putty Goo
Low Temperature Cold Activated Thermochromic Bi-Color Pigment Pink changing to Black at 64F/18C Perfect for Color Changing Slime Silly Putty Goo

This pigment will change color from black to pink at 64F/18C, which is perfect for classroom activities.

 

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! | Source

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.

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 shortest 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!

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    • leahlefler profile image
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      Leah Lefler 2 weeks ago from Western New York

      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 profile image

      Karen Hellier 2 weeks ago from Georgia

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

    • leahlefler profile image
      Author

      Leah Lefler 2 weeks ago from Western New York

      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!

    • profile image

      Peggy Woods 2 weeks ago

      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!

    • leahlefler profile image
      Author

      Leah Lefler 2 weeks ago from Western New York

      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).

    • profile image

      S Maree 2 weeks ago from North/Central Indiana

      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!