Molten Armor

Born of the belief that "the best defense is a good offense", Molten Armor is a Mage spell that both imbues the caster with greater offensive power and protects him by harming his assailants, as well as greatly increasing the possibility of a critical strike. It is a self-buff armor spell. Molten Armor was introduced in the Burning Crusade expansion.

Talent improvements
Impact: The chance to stun is applied to this damage as well. At 5/5, anyone attacking you essentially has a 10% chance to be stunned, giving you time to throw a Scorch in unmolested, or a head start on getting away.

This spell benefits from all other talents that increase damage and critical strike chance for all spells and fire spells. This spell does not trigger the mana replenishment effect from Master of Elements, however.

Fire vulnerability from Curse of the Elements will also increase the damage dealt by this effect.

As of patch 2.3 Molten Armor will no longer trigger Ignite. This is significant because an unexpected DoT from this talent could cause problems when trying to polymorph a mob.

Starting in patch 3.1 Molten Armor was changed to a spirit conversion to Spell Critical Rating. Without the glyph, Molten Armor converts 35% of your total Spirit into Critical Rating. With the Glyph of Molten Armor, 55% of your Spirit is converted.

Patch 4.0.1 reverted Molten Armor to a flat 3% crit chance increase. The talent Firestarter now removes the critical hit chance reduction and instead allows the mage to cast scorch while moving.

Glyph Changes
Glyph of Molten Armor: Your Molten Armor grants an additional 2% spell critical strike chance.

Tips and tactics
The last acquired armor spell is generally considered one of the best for PvE. The large increase to crit chance is unique, and by far the best offensive augmentation available from the armor spells.

The damage to attackers may not seem like a lot, but it quickly adds up if you are being attacked by a rogue or other fast attacker. It's also wonderful for taking multiple mobs at the same time. The damage can crit and is affected by talents like Impact, so additional effects can be triggered by it. Especially when combined with Molten Shields, it will prove a very good defensive combination, as Molten Shields extends the damage caused by Molten Armor to ranged and spell attacks.

It is unclear whether or not this buff can proc while the mage is sitting: this has been included in numerous patches.