Magic and Metal

Natural laws govern our world in all things. Plants grow, animals eat them, others in turn hunt them and an equilibrium is reached, the world turns and tides rise and fall. Magic, despite what some would think is too in balance with nature and so, it too has its counter. 
The most commonly known is Silver. Those that would conceal their true form become revealed by it and burns them on contact with their form. A perfect silver mirror of dwarven make can be used to reveal truths that may be hidden by magic.
Iron burns beings not of this world. Priests use iron dust to exorcise those possessed and those rare hunters of fay and demon use iron weapons to better destroy their foe.
Brass stills the roilings of the Weave that some would evoke to cause harm. Brass collars are common amongst Witch Hunters for this reason and where resources allow, castle walls are veined with brass to protect against destructive magical force.
Within a loop of gold the body is held in this state of existence and negates any attempt to transfer the body by magical means.
Consuming zinc can be used to resist magic that would effect the mind. Some charlatans have used research by renowned scholars to hawk supplements containing mere traces of zinc to those whose minds are unsettled. According to those of greater mind the amount of zinc powder required to cast off magical influence is enough to be near toxic to the consumer and advice is to eject it from the body as soon as is possible.
Lead is used to protect against detection. In addition a space enclosed in lead cuts the weave off from the outside. A famous challenge devised by scholar Ervine Schroding had the greatest mages of the Tristromm Colleges of Magic attempt to kill a small cat that he placed in a lead box without destroying the box. After a full day of casting spells of the highest order the box was opened to reveal Dr Schroding's cat alive and well leading to the use of Schroding's cat being used in regular vernacular being used to mean something you cannot perceive but know the truth of the state before it is revealed.
Magnesium, that most volatile of metals, is used to break protective magical shielding. Weapons of magnesium are prone to spark into flame so more commonly magnesium powder is used in small bunches to disable warding for a time.
There is one kind of magic that has no natural counter for it is in and of itself wholly unnatural. The magic of undeath. Necromancy. For this magic is needed to fight magic.

Type

Metaphysical, Arcane