what metals can the fae directly interact with? im trying to write a short story, and i want to know if the fae could theoretically wield guns and the like
The most consistent metal they cannot interact with is cold iron. Which could ward off evil spirits. You have to understand that iron was different from other metals in that medieval and alchemical philosophy would depict it as having the ability to repel chthonic power and spiritual entities. In a strict academic sense, chthonic referred to deities, spirits, rituals, or power that originated either from the earth or from beneath it (underworld). It related to death and the wealth beneath the earth, sacrifice and blood... but also to the soil of the earth itself, life that bloomed in abundance on the surface, agriculture, birth and rebirth, fertility, and the harvest. It has to do with the world itself, rather than heavenly and cosmic powers originating somewhere unreachable above. In classical works, religious studies, and anthropology it's a highly precise term that refers to powers that exist beneath the earth or in it, distinct from the living surface. Both seed and corpse are buried beneath the soil in the womb of the earth, just as a seed can be planted in the depth of a womb. When it comes to iron, there were two varieties. There was meteoric iron which fell from the sky. Ancient cultures such as the babylonians and egyptians believed this iron from the sky had an inherent celestial power to ward off evil or malevolent chthonic spirits. Many of those beliefs and associations persisted despite the overall rarity of such iron. Meanwhile, terrestrial iron mined from the earth was considered to belong to the world of the chthonic. In the view of medieval alchemy and folklore this meant that iron that was ripped from the earth, aggressively smelted, and forced into unnatural shapes was a major symbol of humanity's domination over the purest form of primeval nature. It was said to have the ability to ward off chthonic spirits because it was their own power being stolen, transmuted, and used against them. Since fae are traditionally counted as chthonic spirits of one kind or another, they too are repelled or burned by this cold iron. Steel, on the other hand, loses that connection with the chthonic earth. it's too unnatural, too artificial, too human. It's also, by the strictest definition, an alloy of iron and carbon, not pure iron alone. So while it has its power in the symbolic representation of human artifice and mastery over metallurgy, it loses its ability to repel chthonic forces. Another metal some might suggest is silver. But this is wrong. Silver was a metal considered by alchemists and folklore to be associated with purity, clarity, and to the moon. It supposedly could burn away spiritual impurities, which meant it was effective against demons (of which vampires are traditionally a type of) and witches (who were considered impure). It was effective as a tool against werewolves because of their connection with the moon and was thought to have some control over them.
To be entirely honest... the field of medieval alchemy and philosophy is a pretty large area of study, and not one I've delved in to much beyond occasional forays. And the nuances of which metals could repel chthonic power whether they came from it or not was deeply intertwined with actual experimental results concerning the process of alchemical purification (they were trying to remove or burn away earthly influences and corruption from base metals in order to make them transmute into the supposedly purest form of metal, which was gold). If I were you, it would be a lot easier and faster to simply stick with cold iron as the one metal that repels the fae. While I would be delighted for everyone to have great interest in such complex and rich topics as medieval alchemical philosophy, unless your actual story has the metals and the reasoning behind their properties as a primary focus or major supporting narrative feature, you would really be better off sticking with just the one metal so as not to lose the actual focus of your story in the addictive pleasure of excessive worldbuilding.
As far as guns go... modern firearms tend to have steel barrels instead of iron ones. But if you're determined to oust steel from your options as well, there are plenty of other metals that could technically be used. Bronze was used historically for cannons and early firearms, though it wears quickly with repeated use. Titanium is an extremely strong and durable metal, though it doesn't occur in a purified form in nature and couldn't be worked with by ordinary blacksmiths. You could always utilize purely fictional metals, either of your own invention or from folklore and mythology. There are plenty of options, but for a short story it's best not to get too caught up in this particular question.
