When metal rusts, oxidation converts its ferrous components into a brittle crust of iron oxide that can't be changed back into iron or steel, only chipped away or chemically transformed into black iron phosphatenote . In video games and some other works, this isn't necessarily true: often, it's a temporary inconvenience that can be set right with a bit of oil. It doesn't matter if the oil in question comes from a machine shop, a lamp, a kitchen pantry, or straight out of the ground. Rub or even just drip a bit of it onto a rusted lock, latch, or other metal gadget, and the device will immediately be restored to perfect working order, gleaming like new. In extreme cases, rusted-out holes and gaps will seal themselves, and even its paint job might be restored.
Probably arises because people conflate oil's use in lubricating jammed or squeaky metal hinges with its use in protecting not-yet-rusted metals from corrosion. Variants in which other substances have an unrealistic restorative effect (e.g. ordinary shoe polish that miraculously repairs cracks and holes in leather) also exist.
Very common in casual and inventory-based adventure games.
- When the Tin Man first appears in The Wizard of Oz, the protagonists don't even realize he's sentient because he's so rusted that he can't even move. After a few quick squirts of oil onto his joints (and a brief scene of him stumbling around), he's practically as limber as any of them.
- In The Wiz Dorothy and the Scarecrow come across an amusement park mechanical man who is rusted. They "slide some oil to [him]" which loosens his joints which lets him move, sing and dance.
- In The Wonderful Wizard of Oz Dorothy and the Scarecrow come across a rusted tin statue and an oil can. They put two and two together to oil the statue, who is the Tin Woodsman.
- Implied in Warhammer 40K, where grot riggers are sent into the bowels of giant mechs and starships with nothing but rags, oilcans and wrenches to fix things. Ork technology relying as much on Clap Your Hands If You Believe as actual mechanical principles, it actually keeps the thousands of tons of rusty metal moving and firing.
- In True Fear, applying oil to the rusted clamp which seals a cabinet will instantly restore it to glistening perfection. In the bonus content, merely dripping oil onto a rust-sealed first aid kit's hinges lets you open it easily.
- Mystery Case Files. In Return to Ravenhearst, dripping oil on the rusty bolts of a culvert's grille instantly restores them, allowing the Master Detective to unbolt it with a wrench.
- In Ancient Domains of Mystery, there are potions called Oil of Rust Removal. When an item is dipped into it, rust will come off.
- In Pajama Sam: No Need to Hide When it's Dark Outside, there is an oil can on the stump outside the riverside shack. You need that to oil King's rusty wheels and navigate the mines.
- In Hugo's House of Horrors you come across a trapdoor but can't open it as the bolt is rusted shut. You need the oilcan from the shed to restore the bolt to open it up.
- In Ratchet & Clank Future: A Crack In Time, a gadget called the Omnisoaker can be used to collect and spray oil onto rusty bolt cranks to make them work.
- The closest real life equivalent is naval jelly, originally invented by USN for rust removal on warships. Naval jelly contains water (65-70%), phosphoric acid (25-30%) and sulfuric acid (1-3%) in a gel matrix composed of a thixotropic polysaccharide (1-3%), alcohol isopropanol (1-3%), surfactant (1-3%) and silica (0.1-1%). The phosphoric acid dissolves the rust (iron oxide)note and then turns the iron oxides into iron phosphate. It can then be washed and painted over.
- Numerous Penetrating Oils are also available that achieve the general idea of the trope- the formulas vary (and are often trade secrets) but the general idea is that a low-viscosity oil can penetrate into the rust and lubricate surfaces, making it easier for them to slide past each other, and for rust and dirt to be worked out from between moving parts. Certain formulations also aid in loosening the chemical bonds between rust and intact metal, which can give the appearance of de-rusting metal as the rust breaks loose and exposes the remaining clean metal underneath.