Last Updated: 200704
According to the MoTP (and other resources) the magical bonus on weapons and armor can vary when a character travels across the planes, generally less by one for each plane removed from the point of origin. Generally, the planes are laid out:
Inner Planes (and Demi-Planes) <> Ethereal <> Prime <> Astral <> Outer Planes.
So a +3 sword created on Prime would be only +1 on the Outer and Inner Planes. All well and good. But exactly where was that item created? If the character has a +3 sword on Prime, but it was created on the Ethereal Plane, then the sword would be +4 when the character adventures to the Ethereal.
While it’s easy enough to assume all magic items are created on Prime, certainly some weapons are created on the Outer Planes (given the many legends of the gods creating weapons and armor and providing them to mortals). To truly account for that, each magic item should be checked when the characters travel to another plane to see if it gets a boost instead of a penalty. There is, of course, no table for that (I don’t think).
At a simple level, the question is which of those 5 “levels” of plane the item was created. Prime is obviously the baseline. Few items would be created on the Ethereal (and even fewer on the Inner planes). Almost no items would be created on the Astral (given the time constraints there). Most non-Prime items would likely be created on one of the Outer planes.
That leads us to a table something like (d20):
1: Inner. If a 1 is rolled, 50% of those items were created on the Ethereal.
18-20: Outer. If a 20 is rolled, 10% of those items were created on Astral.
If an item was created on an Inner or Outer Plane, the specific plane then needs to be determined. For the Outer Planes, determining the plane is as simple as using the Astral Color Pool table. For the Inner Planes, the table for the Curtain of Vaporous Color can be used (readily converted to a table, as it doesn’t include one).