It may be harmful if swallowed, not because ZnS is toxic, but because it can react to form hydrogen sulfide gas, which isn't great for you. Zinc sulfide can be irritating to the skin, so wash your hands after playing with this slime. The slime solution itself isn't exactly toxic, but it isn't good for you, either. Then you turn out the lights and it will glow.
The phosphorescent glow is activated by shining a light on the slime.You can use a spoon and a cup or you can just squish it together with your hands or inside a sealed baggie. Mix together 30 ml (2 tablespoons) of PVA or glue gel solution with 10 ml (2 teaspoons) of borax solution.You can make a saturated borax solution by stirring borax into warm water until it stops dissolving, leaving borax at the bottom of the glass. Again, most of us aren't going to be doing the project in a lab. If you are in a chemistry lab, you can make this by mixing 4 g of borax with 100 ml warm water. The other solution you need is a saturated borax solution.Please read the label on the paint to make sure it is safe enough for your purposes. The zinc sulfide or paint powder will not dissolve. You can find glowing paint at some paint stores or glowing paint powder (which is zinc sulfide) at craft or hobby stores. If you cannot find zinc sulfide powder, you can stir in some glow-in-the-dark paint.
You want 1/8 teaspoon of zinc sulfide powder per 30 ml (2 tablespoons) of solution. Stir the glow agent into the glue gel or PVA solution.For example, you could mix 1 tablespoon glue with 3 tablespoons warm water, or 1/3 cup glue with 1 cup of warm water. You can make a glue gel solution by mixing 1 part of glue gel (either clear or pale blue) with 3 parts of warm water. Most people do not have PVA sitting around their homes. 4 grams of PVA in 100 ml of water is great, but the project still works if your solution is a different percent of PVA (just takes more or less). If you have polyvinyl alcohol, you want to make a 4% polyvinyl alcohol solution. First, let's prepare the glue gel or polyvinyl alcohol (PVA) solution.
The ratio is 3 parts PVA or glue solution to 1 part borax solution, with a little glow-in-the-dark agent thrown in (measurement isn't critical).