Science, Fiction, Life

The Color of Acid

The other day I was playing Starcraft 2 and trying to think of the next topic to tackle here. As I watched a swarm of zerg roaches attack a group of terran marines, I realized that I needed to talk about acid. Two of the new zerg units, the baneling and the roach have acid-based attacks. The baneling is a little suicide bomber that detonates, splashing corrosive acid all over nearby units, while the roach is a nasty armored insect that spews a stream of acid on its foes from a distance.

Banelings doing their thing.

I like both of these units in the game, but they perpetuate a myth about acid that has infested pop culture for years: it is bright neon green. I’m not sure where this idea originated. Maybe it goes back to World War I, when chlorine gas was used as a chemical weapon. It’s not an acid, but it is a nasty caustic chemical that is a sickly green color. Or maybe the green acid idea can be traced back to the movie Alien, where the alien is revealed to have highly acidic blood that looks greenish yellow.

The famous shot of the alien's acidic blood in Alien.

Whatever the origin of the idea, it’s patently false. Most acids are colorless in both their pure form and in solution. Sulfuric acid? Colorless. Hydrochloric acid? Wikipedia says that it is colorless to light-yellow, but I’ve never seen an example that showed any color. Hydrofluoric acid? Colorless.

I don’t know of any acid that is brightly colored, though I admittedly not a chemist. There are probably some nice, colorful organic acids, and it’s certainly possible for acid to be mixed with other colored stuff in a solution, but in the real world acid does not conveniently advertise its corrosiveness by being bright green.

While we’re on the subject, let’s talk about the plausibility of an insect spraying acid, whatever the color may be. This is actually plausible to me. There are plenty of examples of insects that are armed with chemical-based weapons. One of the most famous is the bombardier beetle, which defends itself by blasting a nasty, boiling hot liquid at its attackers. Bee venom contains formic acid, and many ants inject or spray formic acid or other chemicals when they bite.

If we’re willing to suspend disbelief enough to allow the zerg to exist in the first place, I’m also willing to grant that they might use caustic chemicals to attack, since real-world insects do this too.


  1. Mv

    Idk if Im right, but isnt hydrosulfuric acid a bit green/yellowish?

    • Ryan

      Wikipedia doesn’t mention it as being yellow/green. It does say that as a solution it slowly precipitates out sulfur, making it cloudy and (presumably) yellow-tinted, but no mention of the solution itself having a color.

  2. Scvrush

    hey, I really like your website. most acids are not colored!! I think it has to do with artists at blizzard thinking since acid in movies are all green. We should do that too!. I found your site from starcraft2forum. Great site, bro. I myself actually has a starcraft 2 strategy site for all races.

  3. Scvrush

    Oh, I think you put a lot of work into this. If you like, I can make a post on our main page about your site if you could write a short description about your site.

  4. Aegyr

    So the typical acid you’re speaking of would be a simple salt or other basic compound dissolved in water. since we’re talking about things varying 10^-7 plus or minus a bit, the water is going to dominate the aesthetics of it. But if we took an organism with a blood based on the solution, then it would be just like us-our blood is red when exposed to the air, blue in the veins/arteries, and theirs similarly would be a nice mix of something predominately whatever organic compound(easily could be green as plenty of bugs on earth fit that) and the very very small percentage of it that is acidic could be any color without affecting the overall look.

    • Ryan

      Our blood is not actually blue in veins, it just looks that way under the skin:

      But your point that it’s possible for some sort of acidic blood to be bright green is taken. I guess I’m not saying it’s impossible, but I wanted to point out that acid is not generally bright green as it is so often depicted in sci-fi.

      • Jeff

        But on the other hand I don’t think there are a lot of examples in the real world of organisms that can expel acid.

        Here’s a question if you want to look it up: if humans could projectile vomit stomach acid at will, what color would it be? Completely colorless? Something else? How does digestion affect it?

        As for where the pop culture gets it, I’d definitely say the movie aliens, which not only puts it at a green color but is probably the pre-eminent (if not first) popular source of acid as a bio weapon for a monster.

  5. Aegyr

    thanks: my fault for taking somehting commonly stated at face value without ever actually looking into it. Maybe the first waves of zerg sent out are just biological experiements, and against their will were forced to eat gallons of chemiluminescent goo just to make it easy to tell what the effects of their explosions or excretions were.

  6. Starblazer

    The green color in the zerg acid may be a non-acidic component. Some fungi are green, so the green in the acid may be bio-engineered fungal spores that eat away at the target, since the acid alone may not harm many surfaces. The Zerg are supposed to be masters of bio-technology, so many of their attacks are probably due to microorganisms that quickly grow into their target and degrade it.

    • Androkguz

      I believe this is probably it. Enzymes people! The Zerg won’t be vomiting or exploding into inorganic acids, which are the ones we typically see as clear colored. They will be vomiting stuff like the acids in our stomach.
      Banelings probably have a type of enzymes and microorganisms so complex controlling the reaction that they themselves and every other zerg around are immune to it, but not other zergs or metal or plasma shields.

  7. wanderingazn

    There is one acid that is brightly colored: chromic acid (H2CrO4). Before reacting with something else, it’s usually a red or orange color. After reacting, “spent” chromic acid is a dark green. Oh, this acid is also carcinogenic (spent or fresh).

  8. Joshua

    If I had to speculate, I’d say it wouldn’t be an acid. The baneling could have two separate sacs with a thin mucus membrane separating them. Or dozens of separate sacs. When they rupture (when the baneling flexes hard enough to tear them) the two chemicals mix causing an explosive chemical reaction. It could, for example, ignite to thermite high heats for a short period, melting away flesh and armor. Or create something much more powerful and reactive, that breaks down the molecular bonds of whatever surface it touches.

  9. Starcraft 2 Betting

    SOOOO many banelings. Its a beautiful thing. Nothing like see the green goo flying during the GSL. 🙂 Zerg love.

  10. Magic

    Lazers aren’t orange or blue either.

    • G

      1) *Lasers
      2) Yes they are orange or blue or any other colour you can think of.

  11. Luke MIller

    I think the reason for neon green blood is to achieve an “Alien” feel to these creatures. Our blood is red and green is on the opposite side of red in the colour spectrum. The idea is to reinforce the idea that these things are alien and inhuman by having their blood the opposite colour of ours.

    I think this is less of a scientific thing and more of artistic license when it comes to the design of Zerg, Giger’s Alien, Tyranids etc. Green is also seen as gross and icky when it comes out of an orrifice, severed body part etc.

  12. Liquid HuK fighting

    Definety a interesting Idea. Liquid Huk

  13. Starcraft Tips and Tricks

    Cool write up

  14. Alice

    Just heard an appraiser on Antiques Roadshow describe a woman’s skirt in a painting as “acidic green”. Got me thinking about exactly this, and so I googled the phrase and found this article. As a chemistry major, “acid green” confuses me. As you have already mentioned, most acids are colorless. Even then, when testing acids with indicator solution, there are no indicators I can think of that turn green. My grandfather suggested it may come from Granny Smith apples, which people think of as acidic because of their sour flavor, and similarly, limes. Then I must wonder, why not “acidic yellow,” for lemons, or “acidic red” for tomatoes? I remember my father adding baking soda to my tomato soup when I was young because it was too acidic and burnt my throat. I believe my grandfather was on the right track, though. The most likely explanation is that people associate acid with a sour flavor, and a sour flavor to green, unripened fruits. Wikipedia says “…Sourness is the taste that detects acidity…the most common food group that contains naturally sour foods is fruit…”

    But an interesting concept with the aliens and insects. In World of Warcraft and Starcraft, there are a bunch of things that have green acid attacks. Now I must wonder, did Blizzard and make acid attacks green because they associate acid with sour, and sour with fruit? Or as a previous commenter (Luke Miller) suggested, because green is so inhuman? Most insects have green blood because of hemocyanin (as opposed to animals with hemoglobin), and I’m sure that somewhere along the line of Hollywood movies and science fiction novels, this train of thought happened: insects aren’t like humans, aliens aren’t like humans– insects have green blood, therefore aliens should have green blood. When I think of aliens, the first color I think of is green. Then blue. Why is that? There are a lot of aliens in Star Wars that are orange. When I think of nuclear waste, I think green. Specifically, green slime. WHY is that!?

    It’s good to reevaluate the thought process.

  15. Biopower

    It’s green because it’s a mutation of a green algae

  16. TrqR

    Its my favourite units, you can comeback in a game with so many ways: sandwitch attacks, burrow banneling, banneling burst… 😀 love this

  17. ProfFester

    Has chromic acid been mentioned yet?
    Because that is an orange colour.

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