Glue (white clue is cheaper but clear glue will make a clear slime. I even used some glitter glue)
Water (broke open a couple highlighters and soaked wick inside in water for a couple days)
Food Color is optional
You will be making two solutions and combining the two to make the slime. In a bowl, pour your glue out of the bottle and refill with either clear or colored water and add to the glue in the bowl. I used a combination of glitter glue and clear glue. About one ounce of glitter glue and about four ounces of the other. If you want to use food color to color your slime, add three or four drops at this point. I used water that I had soaked the insides of a couple highlighters for a couple days, one blue and one yellow. Stir until the glue and water are combined. In another container, measure one cup of warm water and add one Tablespoon of Borax. Stir until the Borax is dissolved. Now, using a spoon slowly add the Borax solution to the glue solution while stirring. You will almost immediately feel the slime starting to form! You may not want to add all the borax solution depending on how firm you want your slime. Once your slime is too firm to stir, you can take out the spoon and continue mixing with your hands.
The borax is acting as the crosslinking agent or "connector" for the glue (polyvinyl acetate) molecules. Once the glue molecules join together to form even larger molecules called polymers, you get a thickened gel very similar to slime. If you have access to a chemical supply house, try a 4% solution of polyvinyl alcohol instead of the glue for a less rubbery polymer and one that is transparent showing off the color better. Another way to explain the science is to take a necklace and explain that the glue solution is like a pile of links, not connected. Once you add the borax solution, it's like having the links connect into a necklace.
I hope you enjoy making slime as much as our son and I did if you decide to give it a try. I know that not only did our nine year old son enjoy playing with it, so did our four your old grandson, my twenty four year old son, and our son's entire Cub Scout Pack at our recent Blue and Gold Banquet had a blast with it.