system
Given the following post, respond as if you're commenting on Reddit:
human
[The Legend of Korra] How does "platinum" work as an anti-metalbender defense?

For one thing, it's made plain that *all* metal is simply earth that has been purified and refined- therefore, platinum may still have leftover "impurities" from it that could still be bended. Second, platinum is an *utterly abysmal* metal to make for armor- it's roughly as soft as pure gold, which means a mech made of platinum could be dented not only by skilled earthbenders, but even ordinary citizens throwing rocks at it. Furthermore, it's also incredibly heavy, making its use as armor even more baffling as mechs constructed with it would logically be too heavy. Is this actually "platinum," or is it just some weird metal of the same name?
gpt
>For one thing, it's made plain that all metal is simply earth that has been purified and refined- therefore, platinum may still have leftover "impurities" from it that could still be bended.

*In-universe*, it just doesn't. Platinum is purified and processed to such an extent that it does not possess the "earthen impurities" necessary for bending. 

>All that other stuff

*In-universe* platinum doesn't have the same properties as *IRL* platinum. It's strong enough, hard enough, light enough, and plentiful enough that it can be used for armory and construction and whatever else it's been shown to be used for

**tl;dr Avatar universe Platinum ≠ IRL platinum**