Unburn

By calling into existence a reversed form of fire, one with a black flame which radiates shadow and cold, you are able to reverse the effects of a fire. While a normal fire requires flammable material for fuel, the black fire created by this spell instead feeds on the ashes and charred remains of normal fire.

When casting the spell, you choose a point within range for the black flame to start, which initially starts at about the size of a human hand. From this place, the black fire spreads to other burnt materials, similarly to the way normal fire spreads to flammables. The black fire spreads to all burned materials it touches and continues to restore all such materials for up to a full day, or until it can no longer reach burned materials. When this happens, the black fire goes out, though the effects of its passage are permanent and cannot be reversed by effects such as dispel magic.

There are some restrictions however. The results of a recent fire are relatively easy to undo because all of the ashes and other materials are still there. The spell can also be used on older fire, but there is a risk that some of the raw material has been carried off or blown away in the wind. The magic of the spell does not cause most of these materials to return to the scene, though it will call back minor amounts of ash that were wafted away by the hot air of the normal fire. The exact amount of material left unrestored is up to the DM and should be based on the size of the original fire and how long ago it happened.

This spell is effective only on burned materials. It will not prevent a fire, restore hit points lost due to fire damage, or resurrect a creature slain by fire (though it will restore a dead body that was consumed by flames).

Since rust and other tarnish is produced by oxidation, and fire is a form of rapid oxidation, the black fire of this spell will also undo the effects of rust or tarnish on metal, removing corrosion and stains.