Mix 2 parts water to 1 part borax, used 2 Tbsp. water and 1 Tbsp. Borax, stir and set aside. In a new bowl mix 1 Tbsp. Water and 1 Tbsp. white glue and 1-2 drops of desired food coloring.
We made green and blue goop and the kids played all week with it.
I love that it's a liquid and a solid and will even bounce when rolled into a ball, let it sit and it melts in a pile of goop.