Magician spells from LOTR

In the film version of Two Towers, Gandalf uses a variety of spells from Torchbearer — a shield, a light spell, divination…but he also uses what amounts to “heat metal.”

Trying to figure out how that would work in Torchbearer.

Supplies: an ember from a campfire
Factors: weapon, helmet, armor

The magician would cast it before a conflict to disarm an opponent wielding a metal weapon. Most everything on the weapons list except for crossbow, bow, sling, shield and spear. The disarmed weapon cannot be used for the first round of the conflict.

Casting on a helmet: the wearer must throw the helmet. Helmet cannot be worn for the first action.

Casting on armor: leather has no effect but chainmail and plate mail…? I’m thinking impeded for as long as the armor is being worn.

Any other ideas?