Recipe · Magic effect

Color-changing slime that reacts to heat

A slime that changes color where your hands touch it, thanks to a thermochromic pigment: the recipe, how to test it with an ice cube, and safety tips.

By the Slime & Co editorial team · Updated October 18, 2026

Color-changing slime — Photo: Irene Demetri on Unsplash.

DifficultyMedium
Time15 minutes
Makes1 ball
Recommended ageAges 7+, with an adult

This slime changes color when it warms up: wherever you put your hand, it fades or turns another shade, then goes back to its color as it cools. The secret is a thermochromic (color-changing) pigment powder, sold for arts and crafts. Some react at around 88°F (31°C), which is about the warmth of your hand.

Ingredients

½ cup (120 ml) white or clear washable PVA glue
½ cup (120 ml) water
½ tsp (2.5 ml) thermochromic pigment powder
½ tsp (2.5 ml) baking soda
1 to 2 tbsp (15 to 30 ml) contact lens solution (boric acid + sodium borate), added a little at a time

Supplies: a bowl, a spoon, an ice cube or a bowl of cold water for testing.

Why these ingredients? What the activator does and which glue to choose.

Steps

Mix the glue and water.
An adult adds the pigment and stirs well.
Add the baking soda.
An adult adds 1 tbsp of solution, then up to a second one if the slime is sticky.
Knead, then test it: warm hands, an ice cube, or a bowl of warm water.

How do you know it worked?

Lay your hand flat on it for a few seconds: your handprint should show up in another color. If nothing happens, the pigment may react at a higher temperature; try warm (not hot) water.

The most common slime fails

The color doesn’t change: Check the color-change temperature listed on the pigment; add a little more.
The effect fades over time: Thermochromic pigments wear out in sunlight and strong heat. Store the slime in its container, away from light, and never test it with hot water.

Another problem? The Slime Fixer goes through every symptom.

Why does it work?

Thermochromic pigments contain dyes that change shape above a certain temperature: their color disappears or shifts, then comes back as they cool. It’s the same idea as some “magic” mugs.