First, I think that this was probably posted to the wrong board. I think you are looking for the regular DFRPG board.
Second, It seems to me that you might mean enchanted item when you say item of power.
Third, I am not sure exactly what you want this item to do. I suspect that it is intended to either provide extra power for evocation or extra complexity for thaumaturgy, but I am not sure. Please, explain.