Omnisolve, usually written as OmnisolveTM, and also called the Universal Solvent, is a dangerous chemical substance which can dissolve all matter except diamonds.
Omnisolve, the "universal solvent", is a black, thick substance which dissolves anything it touches except for diamond, reducing it to minuscule (albeit very heavy) dust-like residue. It was created by Gyro Gearloose at some point in the 1950's at the request of Scrooge McDuck, who, unbeknownst to Gyro, wanted to use it for mining diamonds, the one substance it could not dissolve. When the Duckburg press did not believe that the substance was a universal solvent, Scrooge proved it to them by dumping the entirety of it onto the ground in front of them, as Gyro and Little Helper attempted to stop him.
Unfortunately, the substance began to dissolve down to the center of the Earth, where it would eventually destroy the Earth's magnetic fields, destabilizing the planet and causing its core to smash it to pieces. Scrooge and his nephews Donald Duck and Huey, Dewey, and Louie were forced to travel nearly to the center of the Earth, where they managed to re-capture the solvent in its diamond jar. Scrooge then used the solvent to destroy the formula for making it, and locked it in a safe in his trophy room, from which it was removed by the master criminal Arpin Lusène, who used it to create a fearsome armor.
Around 2019, in the parallel universe known as the 2017 Continuum, Fenton Crackshell-Cabrera invented his own Universal Solvent for McDuck Enterprises. This version of the Universal Solvent appeared light green, rather than pitch-black. Presumably due to fail-safes built-in by Fenton, it is not as world-ending a threat as the Prime Universe version.
Fenton showed it to Gandra Dee on their first date. Fenton hoped to use it for terraforming, but Gandra suspected Scrooge would use it for diamond mining. When Gizmoduck fought Mega Beaks later that evening, Beaks weaponized the Universal Solvent, causing the lab's roof to cave in.
By covering an object in glue mixed with diamond dust, it was possible to permanently coat it in Omnisolve, thus creating a nigh-indestructible weapon. This happened twice: first with the Omnisolve Umbrella, created by Gearloose himself, which came in handy to Scrooge and co. many times during the journey to the center of the Earth.
But more famously, when the master thief Arpin Lusène broke into Scrooge's Money Bin, he stole the jar of Omnisolve, a bag of diamond dust, and a medieval suit of armor. He then coated the armor with a mixture of the diamond dust and glue, and painted the Omnisolve onto all of it but the undersides of the hands, bottoms of the feet, and handle of the sword, with a diamond brush. Wearing it, he was almost unstoppable, until Scrooge pulled a rug out from under his feet, causing him to fall 12 floors onto a cart of diamonds. Scrooge and his nephews pulled Lusene out of the suit, and Scrooge added the suit to his trophy room, but Lusene escaped.
Eventually, he returned and recaptured the suit, adding a hook to the back of the suit to keep him from falling through the floor if he fell again. This time, however, Scrooge lured him into a diamond room and trapped him there until his suit dissolved all of the air in the room, causing him to pass out. Lusene escaped again, but the suit was sent to space.
Years later, the Omnisolve Umbrella was used by Donald Duck, Gyro Gearloose, Magica De Spell, and Little Helper to destroy a meteor that was set to destroy the Earth. They succeeded, but the the Umbrella was lost in space, where it began to destroy McDuck satellites. This means that, unless Lusene has managed to get the suit back again, there is currently no Omnisolve left on Earth. [FANWORK]
Behind the scenes
Omnisolve first appeared in 1995 in The Universal Solvent.