Inscribed along its length with wicked-looking runes, this 3-inch-long nail is made of black metal and gives off a faint, eerie blue glow. Powered by strange necromantic magic, the nail allows a spellcaster to cast spells within a magic dead zone by drawing on the caster’s life force to power her magic. To be effective, the nail must be placed alongside the flesh in an empty magic item slot (excluding eyes, head, and headband). In a process that takes 1 round, the nail melts painlessly into the wielder’s flesh before taking effect (removing the nail is also painless and takes 1 round). Once the nail is in place, its wielder can cast within a magic dead zone up to one spell of each spell level she knows or has prepared and could normally cast. If she wishes to cast additional spells in the magic dead zone, she can do so up to her normal limit, but each additional spell she thus casts causes her to become fatigued and requires a successful concentration check (DC = 15 + the spell’s level) or the spell fizzles. If the nail of blood would cause the wielder to be fatigued when she already has the fatigued condition, she becomes exhausted. She can’t use the nail of blood to cast additional spells while she is exhausted, no matter what effect caused her exhausted condition.
These planes have no magic at all. A plane with the dead magic trait functions in all respects like an antimagic field spell. Divination spells cannot detect subjects within a dead magic plane, nor can a spellcaster use teleport or another spell to move in or out. The only exception to the "no magic" rule is permanent planar portals, which still function normally.
Dead-Magic Wall: Dead-magic walls incorporate cold iron runes that negate all magic passing through, as described in the spell antimagic field. If a room is enclosed on all sides (including the ceiling and floor) by dead-magic walls, the area within functions as an antimagic field. Creating a dead-magic wall requires the spell antimagic field, the expenditure of 3,000 gp for each 5-foot-wide-by-10-foot-tall section of wall, and the creator to have the Craft Wondrous Item feat.
An invisible barrier surrounds you and moves with you. The space within this barrier is impervious to most magical effects, including spells, spell-like abilities, and supernatural abilities. Likewise, it prevents the functioning of any magic items or spells within its confines.
An antimagic field suppresses any spell or magical effect used within, brought into, or cast into the area, but does not dispel it. Time spent within an antimagic field counts against the suppressed spell's duration.
Summoned creatures of any type wink out if they enter an antimagic field. They reappear in the same spot once the field goes away. Time spent winked out counts normally against the duration of the conjuration that is maintaining the creature. If you cast antimagic field in an area occupied by a summoned creature that has spell resistance, you must make a caster level check (1d20 + caster level) against the creature's spell resistance to make it wink out. (The effects of instantaneous conjurations are not affected by an antimagic field because the conjuration itself is no longer in effect, only its result.)
A normal creature can enter the area, as can normal missiles. Furthermore, while a magic sword does not function magically within the area, it is still a sword (and a masterwork sword at that). The spell has no effect on golems and other constructs that are imbued with magic during their creation process and are thereafter self-supporting (unless they have been summoned, in which case they are treated like any other summoned creatures). Elementals, undead, and outsiders are likewise unaffected unless summoned. These creatures' spell-like or supernatural abilities may be temporarily nullified by the field. Dispel magic does not remove the field.
Two or more antimagic fields sharing any of the same space have no effect on each other. Certain spells, such as wall of force, prismatic sphere, and prismatic wall, remain unaffected by antimagic field. Artifacts and deities are unaffected by mortal magic such as this.
Should a creature be larger than the area enclosed by the barrier, any part of it that lies outside the barrier is unaffected by the field.
This gives rise to a few questions on the interactions between them
1) Does a Nail of Blood allow casting in a dead magic plane?
2) Does a Nail of Blood allow casting in dead magic walls?
3) Does a Nail of Blood allow casting in an Antimagic Field?
1) Probably it will, but the part about it working as an Antimagic field is problematic.
The item come from People of the Wastes and while there isn't a clear definition of what is a "dead magic zone" in any of the Paizo books about the campaign world (or, at least, I am unable to find one), it is clear that it isn't a magical effect that suppress other magics like Antimagic Field. It is an area where the magical energy is absent.
An Antimagic field will suppress the magic of the nail (it has no provisions against that), while it has provisions for working in a dead magic area, so it will work in those.