"The discussion of the nature of polonium was renewed by the discovery of Marckwald that a substance similar to polonium, of which the activity did not decay with time, could be separated from pitchblende. ...The radiations from Marckwald's substance are similar to of polonium, for no penetrating rays are present. The radiations are very intense. They have a marked photographic action, and cause many substances, like zinc oxide and the diamond, to phosphoresce brightly. The strong luminosity of the under these rays can be utilized to distinguish the diamond imitations, for glass is only slightly phosphorescent in comparison. ...Marckwald ...states that his preparations have preserved their activity unchanged while the polonium of the Curies undoubtedly loses its activity in the course of a few years."