Combine 2 cups Elmer's glue with 1 1/2 cups warm water in a medium bowl. Mix until thoroughly combined. Add a few drops of food coloring to the mixture to change the color.
Mix 1 1/2 tablespoons Borax with 1 cup of hot water in a separate small bowl. Once most of the powder is dissolved, slowly pour the hot water mixture into the center of the glue while stirring constantly.
Stir the Borax and glue until it begins to form a ball, then start kneading it with your hands. Add more Borax if it is too sticky to handle. It will take approximately 5-10 minutes of kneading to combine the ingredients. The finished gak will have a glossy finish to it.
Save your gak in a zip-lock plastic bag or air-tight container to keep it fresh for future use.