Stainless Steel

Have you ever dreamed about becoming the perfect knight in shining armour? Do you want to be seen in an absolutely blinding glistening plate armour without ever lifting a finger? Are you too poor to afford pages to shine your armour for you? Don't you fret, we have a perfect invention for you! All maidens and maidbeginnings will be at your feet in no time!
There are rumours that such an alloy of steel exists that is immune to rust and any other metal afflictions that could damage it as time go by. And you don't even need to do anything to make it that way! No cleaning, no polishing, no special oils and other supplies that all the peddlers are offering at discounts at the biggest tournaments of the years. Just, pure, shiny, amazing, flexible and hard metal. Just like the knights like it.
While some thing that this is just a rumour and a foolish little tale, for some blacksmith figuring out how to make an armour that does not decay is better than learning how to actually transform metal into pure gold. Gold is too heavy to travel with and knowledge of secret techniques and materials can be sold over and over again by any warlord that so desires it.
Needless to say that if you stumble upon a set of armour or a weapon in a forgotten tomb and it seems like no time has passed for these items, rest assured that even if they are cursed, they are definitely worth taking back to the surface no matter what. Even if it means that you will want to try to sell them as soon as possible, these things go by like hot cakes.
Although some knights and warriors out there firmly believe that one should take care of their weapons and armour and that it is just part of the warrior code and discipline to know how to take care of your things well so they serve you in many future battles. And bloodstains and chipped edges sometimes look really badass.