Borax, elmers glue, water and food coloring. I posted a pic of the Borax because finding it was the hardest part of the whole project for me.
So first you combine in one bowl 2/3 C of white glue and 1/2 water. Add food coloring to this bowl if you desire. Then in another bowl stir together 1/2 C of water and 1 teaspoon of the Borax. Then pour the Borax water into the glue water. The reaction is pretty fast