When doing a foging test, I coat a piece of ordinary paper, then let it dry in total darkness. I then cover half of the coated area and expose the other half. I then wet the paper with filtered water, then developer. Lately, only the exposed area that had been exposed becomes black and the unexposed area stays the color of the paper(white). This is as it should be. HOWEVER,If I turn on the lights and therby expose the previously unexposed half, the "unexposed" area, in the course of several minutes, becomes blacker than ithe initialy exposed half. Why?