slimeSometime last winter our friend Jeremie took a turn teaching the kid’s Sunday School class. Jeremie is one of three hard-core geeks in the congregation. He’s a graduate student and teaches physics at Clarkson University.

Jeremie thought it would be cool to use the Sunday School class as an opportunity to make slime. I can’t remember what slime had to do with the Bible. I’m sure it related somehow. But the sheer joy of making your own slime in Sunday School has long overshadowed any other point. Maybe the point is simply to rejoice that the universe is made in such a way that slime exists and that even you can make it.

I’m not sure which slime recipe Jeremie used. There are a few possibilities. But ever since, the kid has been wanting to replicate the manufacture of slime at home. Over the weekend, we finally did it.

Here’s the recipe we used:

Ingredients:

  • 1 tsp Borax — Na2[B4O5(OH)4]·8H2O
  • 4 oz Elmers glue — (C4H6O2)n
  • 1.5 cups water — H2O
  • 8 drops food coloring (optional)

How To:

  1. In one bowl dissolve borax in 1 cup of water.
  2. In a second bowl, dilute the Elmers glue into a half-cup of water, and optionally, add food coloring
  3. Combine the bowls’ contents and kneed by hand until slime forms.
  4. Drain excess water and continue to kneed by hand until slime coheres and stops sticking to your hands.

Why this works:

Elmer’s glue is a polymer. Which means that it’s a bunch of molecules made up of carbon, hydrogen and oxygen that want to lock together to form a solid. That’s why, when glue dries, it gets hard. All those molecules lock together and become a hard piece of plastic. It’s the water in the wet glue that keeps the glue molecules from linking up. When the water evaporates (the glue dries), the glue molecules get to do what they want to do — the glue gets hard.

So, with just the glue and the water, all those molecules just flow around one another haphazardly. When you add the borax to the glue, the borax molecules form molecular slip-knots between the glue molecules, so instead of tumbling around each other haphazardly, the glue molecules link up in long strands that slide past each other through the slip-knots. This kind of slip-knot chemical link makes slime kind of like a solid, because the molecules aren’t completely free to go anywhere they want any more. But it’s also kind of like a liquid, because they are free to move around through the borax slip-knots. Cool.

You need to keep your slime from drying out though. Because without the water, those glue molecules are eventually going to stop sliding around and lock into place, just as if it were regular glue. Then you’ll have a solid chunk of — well — hard plastic.