Patina (blue rust) of stainless steel plug lock

"I want you to exchange the key because you are moving in."

It was the key to the storage room.It was said that the blue rust (patina) had progressed considerably and there was no key.I didn't see the manufacturer name, but is it AGE in terms of structure?It was also partially damaged (shaft holder).

By the way, this patina (blue rust) is a wise rust that also has a bactericidal action.When I looked it up,

Green'sRustWhat is your true identity? BrassYou can leave accessories dirtytagGreen stains, this is a substance called patina. Patina is copper that is formed by oxidizing copper.Rust. BrassIs a copper alloy made by mixing zinc with copper, so it reacts with sweat and water to form turquoise rust.

Brass was a copper alloy.Convinced again (I feel like I learned in junior high school).
If this happens, it cannot be easily removed. (There are polishing methods for baking soda, Picard, and gloss Nosuke.) It will be replaced.
Since it is not completely compatible in size, it was replaced with a Daimatsu product by additional machining of the door.

I see it in library stacks such as universities, but what did the designer think that it was also used in the storage room of condominiums?I wonder if the lock needed to be strong because the door was heavy made of iron.