Repulsion, Propulsion, Conversion, and...What's this?? That's right! Thanks to mods, these three gels have become the new-age laws of robotics. That is, something based on Sci-Fi, that there are three of, not counting the hundreds of extras that people have added over the years, or, year. Only two being Adhesion Gel (Makes objects stick to walls, etc.), and Electrocution Gel (I'm not sure what that does but I guess the name is informative enough), both of which are purple.
Appearences/EffectsThe order in which they were created is this:
Repulsion gel, which appears as a thick blue substance, and was originally made as pudding that makes you puke, is now marketed as a blue liquid that you put on your floor to turn it into a trampoline, or in other words, make you bounce on it. It was Apertures second product (after the portal gun), invented in the 1940s.
Propulsion gel, which appears as a thin orange substance, and was originally made as laxative pudding (the fact that it acts as an oil slick reduces the possibility of digestion), is now marketed as an orange oil slick that you put on you floor to make you run faster. It was invented in the 1970s, shortly before Black Mesa started stealing Aperture's ideas. Obviously there was a link between the two.
Conversion gel, which appears as an oddly-texured white substance, and was never a pudding, was invented as a last resort in the 1980s after Aperture science went bankrupt. When in an experiment involving "portals in space", Cave Johnson discovered that the moon was ideal for portal placement. (Which is also the reason that Chell is still alive) He began to experiment using moon rocks for conversion Gel.
What Happened nextCave Johnson became ill from exposure to moon rocks, and told the "Lab Boys" that
they would have to start working on a computer that they could "Pour him into". He demanded that, if he died before the computer was done, then Caroline would be put in charge. He also demanded that, no matter any protests she might have, Caroline would have to be "poured into sed computer". Cave johnson died, and Caroline became GLaDoS. She killed everyone but Chell, and then Portal happened.
Personally, I'm glad Cave Johnson died before GLaDoS was finished, because what kind of boy is named GLaDoS? Also, Caroline=GLaDoS may have killed everyone, but I'm pretty sure that Cave=GLaDoS wouldn't have made all the turrets sing an entire opera on "Goodbye, My Daughter" when Chell left. That's Right. DAUGHTER.
Epilouge: We want more!
After Co-op, I think we can all see what needs to be done. New portal colors=new Gels. Purple and red. Adhesion and electrocution. You know what to do...