Iron used to repel spirits
In theory, if ghosts do exist and they do use electromagnetic energy to manifest, then hypothetically one could use a conductor of electricity, such as iron to drain or ground out the energy from the spirit. Therefore, touching a grounded, iron object to the spirit itself would drain all usable energy from that spirit. Based on this theory, many cemeteries are enclosed by iron fencing to keep the spirits in. Also, it has been said than an iron horseshoe placed at your front door will bring good luck by keeping evil spirits out.
Sam and Dean feel cold iron is the best way to repel a spirit. They usually employ fireplace pokers, and on at least one occasion a wrench. Their hunting relatives also made use of iron. A house belonging to the Campbells, Mary's family, was outfitted with iron fixtures. John owned an iron axe that is eventually used by Sam to behead Leshii.
Sam and Dean gain firsthand knowledge of the effect of iron on spirits when they astral project with the assistance of Pamela Barnes in 4.15 Death Takes a Holiday. They find themselves trapped when a demon, despite being burned by the metal itself, encircles them with an iron chain.
- 1 Episodes
- 1.1 1.17 Hell House
- 1.2 1.18 Something Wicked
- 1.3 1.19 Provenance
- 1.4 2.06 No Exit
- 1.5 2.21 All Hell Breaks Loose: Part One
- 1.6 2.22 All Hell Breaks Loose: Part Two
- 1.7 4.02 Are You There, God? It's Me, Dean Winchester
- 1.8 4.06 Yellow Fever
- 1.9 5.10 Abandon All Hope...
- 1.10 6.09 Clap Your Hands If You Believe...
- 1.11 6.18 Frontierland
- 2 Wrought Iron Lore
- 3 References
Sam uses an iron poker to repel Melanie Merchant.
The phoenix Elias Finch was unable to escape from the jail or handcuffs because they were made of iron.
Wrought Iron Lore
Wrought iron is sometimes asserted to repel, contain, or harm ghosts, fairies, witches, and/or other malevolent supernatural creatures. This belief continued into later superstitions in a number of forms:
- Nailing an iron horseshoe to a door was said to repel evil spirits or later, to bring good luck.
- Surrounding a cemetery with an iron fence was thought to contain the souls of the dead.
- Burying an iron knife under the entrance to one's home was alleged to keep witches from entering. 
Cold iron is also used for similar purposes. However, cold iron is pure iron that is not smelted out of ore, but hammered pure without melting.