The Science of Slime and the Best Homemade Recipes
The Science of Slime: The Chemistry of Slime and the Best Homemade Recipes to Try
Let’s talk slime. Yep, that stuff that kids everywhere are obsessed with and moms are tired of digging out of the carpet. There are bazillion slime recipes online, and we all know by now kids love slime.
But do they know how slime works? Is it a solid or a liquid? How does it stay together like it does? What is the difference between borax and liquid starch slime recipes?
Making slime has value as a sensory activity, but it also has value in terms of learning more about what makes slime, slime. So let’s take a look at the science of slime.
(Plus you can grab the free printable with step by step instructions on how to make the easiest slime that you can customize any way you like at the bottom of this post!)
So what is slime? And how does it retain its sliminess? This is the science behind the sensory fun. The big things we are going to look at are:
Type of Matter
Solid or Liquid?
First question: Is slime a solid or a liquid? It doesn’t act quite like water, but it doesn’t hold its shape like a block does.
In a solid, particles are tightly packed together. They are so tightly packed they don’t change shape unless acted upon by an outside force. These are things like tables, chairs, blocks. They hold their shape and are, well, solid.
In a liquid, the particles can move around each other take the shape of the container they are in. Volume stays consistent unless acted upon by outside forces. So what is a slime?
Slime has characteristics of both solids and liquids. So what is it? Slime is a non-Newtonian liquid. (Remember ooblecks? Those are non-Newtonian liquids too! Learn how to make them here!) Non-Newtonian liquids are liquids whose viscosity changes based on the forces applied to it.
What is viscosity? Viscosity is a property of liquids that describes how fast the liquid flows. Think of water. If you pour it out of a container it flows pretty quickly. Now think of peanut butter. (Yep, peanut butter is a liquid.) If you try to drop it off a spoon it flows very slowly. We say it is more viscous.
What does this mean for slime?
So what does viscosity have to do with slime? Well, as a non-Newtonian liquid slime changes how it acts based on the forces applied to it. This means you can manipulate slime. When you roll it around your hand or squeeze it, slime feels pretty solid, similar to play-doh. But as soon as you stop applying pressure slime oozes and acts more like a traditional liquid.
It isn’t just viscosity that makes slime act like it does. How does slime stay together as a mass? This is the result of polymers. Polymers are simply chains of repeating molecules that stay linked together. (The pieces are called monomers. Mono=one, poly=many.) These chains can stretch and move, helping to give slime it’s bendy-ness.
Polymers are all around us. Silk and wool are polymers, so you might be wearing some right now. DNA and protein contain polymers as well, so you are currently an example of a polymer in action. (Too bad we can’t bend and stretch like slime!)
When you mix the ingredients of slime together you are linking polymers. (Sounds high tech, doesn’t it?) Glue is a common slime ingredient. It contains polymers that slip around past each other as glue is a liquid. It can be quite viscous, remember that means it doesn’t flow quickly.
As you add in additional ingredients, like Borax or contact solution, those polymers start cross-linking. They join up and create a lattice-like structure that is more solid. This creates your slime that holds itself together better than a regular liquid.
The Short Version
If you are looking for the short answer for why slime is slime, here is the summary of what I talked about above. Slime is a non-Newtonian liquid, meaning it changes its behavior based on the forces put on it. If you are kneading it the slime is firm like a solid. If you just leave it alone it oozes like a liquid. These different behaviors are a result of viscosity, or how quickly a fluid flows.
What makes the slime come together? Glue has polymers or long chains of repeating molecules. Adding in a slime activator connects those chains into cross-linked polymers. This gives the slime its structure.
Why Different Slime Recipes?
Why are there different recipes for slime? Well, the simple answer is that there is more than one way to cross-link polymers and make non-Newtonian liquids. There is more than one way to bake a cake, right? Same with slime. Borax, liquid starch, contact solution, they all play the same part in the reaction. It really comes down to what you have on hand. All of these will make a traditional slime product.
Slime is also an amazing sensory activity and a great way to enjoy sensory STEM play. Learn all the benefits of sensory play—> The Big Benefits of Sensory PlayThe Big Benefits of Sensory Play.
Basic Slime Recipes
Most slime recipes follow a similar formula. Mix glue with some sort of slime activator. (This is your Borax, liquid starch, or contact solution.) That’s really it. You can make the slime as runny or solid as you like by adding more water or glue.
You can also put in add-ons to make it more fun. These are things like glitter, or coloring, or even heat changing compounds that make your slime change colors as it gets warm.
A Note on Borax
Borax has come under a harsh spotlight in the past few years, making some people wary of using it in slime. (It makes awesome crystals too!) Borax is also known as sodium borate. It is a naturally occurring material that is great as a cleanser, as a buffer, and a number of other things.
I do want to point out that borax is natural, it is mined out of the earth. So the argument that we should only use natural materials is moot because Borax is natural. Used in high enough quantities it can irritate that skin and have some negative health effects. But that is in extreme cases. The occasional contact your child has with Borax when making slime is unlikely to cause health issues.
As always, use your best judgment as a parent. But making slime with Borax isn’t likely to harm your child. (And contact solution contains boric acid, which is why it also works as a slime activator.)
Tons of Possibilities
Once you have a basic slime recipe that works for you, the sky is the limit! You can add colors, glitter, scents, or anything else you can think of. Adding small foam balls makes a floam type slime.
Mixing colors can give a rainbow effect. You can even make slime that glows in the dark. I actually love kits for this kind of thing because they give you everything you need plus ideas on how to make some pretty fancy slime.
Recipes to Try
How I Make Slime
Here is the recipe I use to make slime at home.
Put 4 ounces of Elmer’s glue into a bowl and mix in about 4 ounces of warm water.
Add in any extras you want. I add food coloring, glitter works, or oils if you want scented slime.
In a separate bowl mix 1 teaspoon Borax with 1/2 cup water.
Start adding the borax solution to the glue bowl, spoonful by spoonful an stir. As you add in the borax the slime will start to stick together. Add enough borax until you get the slime consistency you want. Use your hands for a final knead and have fun!
I like using Borax because I can buy it easily at the grocery store, and we use it to make awesome crystals. (And my husband doesn’t like it when I steal his contact solution.) You can order liquid starch to use online. Store your slime in Tupperware when not in use, and be sure to wash your hands after playing with it.
Other Recipes That Look Cool
Toy Story Alien Slime
Use green food coloring as your add-on ingredient. (Feel free to sprinkle in some glitter too.) Then add in googly eyes to make it look more like the aliens from the movies!
Clear Glue Slime
Making clear slime is super easy and super cool for kids. It is so simple to do too! Take the recipe I listed out above and substitute clear glue for regular white glue. Simple clear slime!
Princess slime adds a touch of sparkle and shine to your sensory play. Make clear slime by using the basic slime recipe with clear glue. Add in glitter or sparkles to give the slime the royal treatment.
Color changing slime can be super easy too! Use thermochromic or photosensitive glue to make slime that changes color! Slime can change colors by adding heat (the heat of your hands works) or by putting UV light (a blacklight) on it.
This slime is awesome for talking about the differences between warm-blooded animals and cold-blooded animals.
I know, glitter can be a bad word when it comes to crafts. Once it is in your house you never really get rid of it. But it is so festive and fun! So I trust my friend Valerie from Chronicles of a Babywise Mom when she says this recipe contains the glitter. Pretty slime without my house looking like we dragged a disco ball through? I’m in.
This slime adds in a special ingredient clay. It creates a smoother slime that appears to spread like, well, butter. This recipe from Tatertots & Jello is unique. This very smooth slime could be very soothing for kids looking for sensory calming.
This recipe combines slime fun with magnet fun. Win! As an add-on, you use iron oxide powder, which gives the slime its magnetic quality. You do need powerful magnets to get this to work, your average refrigerator magnet won’t necessarily cut it. But you can have so much fun with magnets, it is a worthwhile investment. Check out Frugal Fun 4 Boys to learn about this one.
Slime-containing borax should never be eaten, but we all know little ones like to taste things. So you can make edible slime! You can make it out of marshmallows, jello, chia seeds, they have a lot of options. A few good ones to try are gummy bear slime and pudding slime.
Slime It Up!
Slime is something kids are just drawn too. It is fun as a sensory activity, but it is also important to take a moment and learn why slime behaves as it does. Little kids can practice observing the differences between states of matter like solid and liquids. Older children can start to learn about how molecules can link up to form polymers and how they join in different ways. Plus you can add in so many more components to make your slime even more interesting. So get back to the slime. Just keep it away from the carpet.