Abjuration
Level: Sorcerer 6, Wizard 6
Components: V, S, M
Casting Time: 1 standard action
Range: Close (25 ft. + 5 ft./2 levels)
Target: One inter-planar gate or portal
Duration: Permanent (D)
Saving Throw: None
Spell Resistance: No
You cast a silver bar in the direction of the portal and it vanishes, becoming a semi-translucent net of silver magic that briefly encases the portal before disappearing.
You can permanently seal an inter-planar gate or portal. The spell prevents any use of the portal, although seal portal can be dispelled by a dispel magic spell. A knock spell does not function on a sealed portal, but a chime of opening dispels seal portal if seal portal was cast by a spellcaster of lower than 15th level.
Once a portal is opened, seal portal does not remain in effect and must be cast again.
Material Component: A silver bar worth 50 gp.
Source: Spell Compendium (Page 181)