Slime is mixed in two stages. First, dissolve 1 teaspoon of borax in 1 cup of water, stirring well. In another bowl, mix 1/2 cup of water and 1/2 cup of glue, and add the food coloring if desired.
Add the glue mixture to the borax, and stir with a spoon to combine. Continue stirring until the mixture becomes difficult to stir. Move the slime into another bowl, and continue mixing by hand. Some water may remain in the first bowl.
Continue working the mixture until it becomes flexible. The slime becomes firmer and more like putty the more it is handled. As it stiffens, slime can be molded and shaped, although it does lose its shape over time. The food coloring in the slime can stain, so use it only on protected surfaces if you have colored it.
Slime sometimes evaporates or grows mold, so store it in a zip lock bag in the refrigerator to keep it fresh between uses.