Measurements on the angular correlation of two-photon annihilation of positrons within 10 milliradians of 180° show that amorphous materials, known or expected to have a long-lived component, have a more pointed distribution than crystalline materials, as though a narrow component were present. The former group includes fused quartz, Teflon, polystyrene, polyethylene, paraffin, Lucite, and glass; the latter, crystalline quartz, aluminum, magnesium, copper, graphite, and sulfur crystals. Cane sugar, either as "crystals" or as a plastic material, is empirically classified with the narrow-component group. Magnetic experiments up to 16.3 kilogauss cause a transfer of 3 to 4% of the annihilation events into the narrow component from the rest of the events, when the narrow component already exists in the material in agreement with the assumption that a triplet state of a positron-electron system is being quenched. Experiments under way are designed to estimate the positron-electron overlap by measurement of the field dependence of this effect. A preliminary experiment on possible diffusion of annihilation centers is described.