White school glue
Baking soda
Contact lens solution with boric acid or sodium borate
Food coloring, optional
Pour glue into a bowl
Add a small amount of baking soda
Mix well
Add food coloring, if desired
Add contact lens solution a little at a time
Stir until the slime starts forming
Knead the slime with your hands
Add more contact lens solution if it is too sticky
Add a little more glue if it is too stiff
Store in an airtight container