When doing this test, I always use "virgin" devloper. Since I have not used fix at this point, would not the "exposed" area gain as much exposure from the white light after development as the initialy unexposed area. Yet the unexposed area eventualy becoms darker than the exposed area. Its as if the first exposure of exposed area is less 'potent" than thesecond time I turn on the white light and expose the entire area. It is as though the emulsion is "faster" in the pressence of developer.