Frequently Asked Questions About Slime

Slime Science FAQs

Got questions about slime science? The key to getting the slime you want is using the right ingredients.
Got questions about slime science? The key to getting the slime you want is using the right ingredients. MamiGibbs / Getty Images

Making slime is a fun and easy science project and activity for kids. However, there are lots of different types of slime, so you may be unsure which ingredients to use, how to color slime, whether you can make substitutions for chemicals, etc. Here are some of the most common slime questions and answers:

  • How do I make translucent slime? How do I make opaque slime?
    Basically, your slime will be about as transparent as the glue you use to make it. If you use white school glue, then your slime will be opaque. If you use translucent clear or blue glue gel (or another see-through color), then your slime will be translucent. Slime made using soluble fiber will be in between. You can still see through it, but it might not be completely translucent.
  • Can I mix the slime solutions in advance?
    Yes, you can prepare the borax solution and glue solution days or weeks before actually making the slime. Borax is a natural disinfectant, so you don't need to worry about it going bad or getting moldy.
  • My slime has leftover liquid. Did I do something wrong?
    No, your slime is fine. When you mix ingredients, only a certain amount of water is needed to produce the polymer. Excess stays behind in the bowl. It's fine to throw it out.

  • Are borax and boric acid interchangeable? Can I substitute one for the other?
    Borax and boric acid are not the same chemical; borax [Na2B4O7·10H2O or Na2[B4O5(OH)4]·8H2] is a salt of boric acid [B(OH)3]. When you dissolve borax in water, it forms boric acid and also the borate ion. If you have boric acid instead of borax, it can be used for slime, but the recipe is somewhat different. Either dissolve the boric acid in water (if it's a powder) or else use buffered saline solution (i.e., for contact lenses). Mix the liquid with white school glue and a bit of baking soda (sodium bicarbonate). You can color the slime if you like. This slime with be less gooey and more stretchy or putty-like than borax slime.
  • Can I make slime without borax or boric acid?
    Absolutely! There are many recipes for slime that don't require borax or boric acid. However, be aware some products contain the chemical (such as saline solution and some detergents). Not all of the borax-free slime recipes listed online are really borax-free! These recipes don't contain the chemicals.
  • How do I color slime?
    If your glue is tinted, then your slime will be colored. You can mix food coloring in with either slime-making solution. You can also add glitter or other decorations. You can also mix in glow powder for glowing slime, thermochromic pigment for color-change slime, or iron oxide for magnetic slime.
  • How long can I keep my slime?
    Slime doesn't go 'bad', but you may want to toss it if it develops mold or if it dries out. Refrigerated slime, kept in a baggie, should last for a couple of weeks. I have made slime that has lasted months in a sealed bag, unrefrigerated. If slime contains borax, it shouldn't go bad. Edible slime recipes should be chilled for storage and thrown out