In my campaign, bronze is rare. Copper and arsenic create a form of bronze. These type of weapons are +1. Rarer is the knowledge of copper tin bronze. Bronze made of copper and tin is harder and less brittle than copper and arsenic. Weapons made of copper and tin are +2. The knowledge of smelting iron is extremely rare in my campaign. Iron weapons are +3. Wrought iron weapons are +4. Steel is extremely rare. Steel weapons are +5. This is without the need for magic.
Creating steel in the ancient world normally involved harnessing a fire elemental and an air elemental to power the furnace. The result is not magical, but magic is involved.
Magical weapons should have a history and a reason for their creation. I previously blogged about the creation of the Cursed Sword of Zahair.
Cursed Sword of ZahairAn ornate sword covered with filigree, gemstones, and runes down the center of the blade. The sword appears to very valuable. On deeper inspection, the gemstones are only polished glass and semi-precious stones. The filigree is not of gold but lesser metals. The magical runes on the blade read, "Liars believe their own lies". The sword gives its owner the ability to spin wild tales of high adventure where the owner defeated powerful monsters. When the owner tells a wild tale, the sword makes them believe with all their heart the lie they are telling. The owner becomes convinced their exploits are the result of owning the sword. The owner will willingly face certain death to possess the sword. As a weapon, the sword is almost useless. When facing an adversary the owner will turn and run at the first opportunity then later tell a story of how they defeated the adversary after a long battle.
I found the picture of the sword here.