Gak is made by combining white glue, powdered Borax and water. Gak, sometimes called slime, goop or oobleck, is a slippery, putty-like material that behaves sometimes like a solid and sometimes like a liquid.
Mix glue with water
Combine 8 ounces of white glue, such as Elmer's brand, and 8 ounces of warm water in a mixing bowl. Stir well. If colored Gak is desired, add several drops of food coloring.
Add a 1/2 teaspoon of Borax powder to 1/2 cup of warm water and stir. It isn't necessary for all of the powder to dissolve.
Add Borax solution to the glue mixture
While stirring the glue mixture, add the Borax solution a little at a time. The mixture will begin to stiffen immediately. Continue adding the Borax solution, mixing with your hands until the desired consistency is achieved. Gak behaves like a liquid when poured, but it stiffens if punched or squeezed. Store Gak in a plastic bag in the refrigerator.
Gak can be made using cornstarch instead of Borax. The simplest recipe involves mixing 1/2 cup of liquid cornstarch with 1 cup of white glue until the desired consistency is achieved. Gak made with cornstarch isn't as rubbery as Gak made with Borax.