Minerals with well-defined TL peaks are likely candidates for archaeological dating materials; they are short-listed by a trap depth measurement using the initial rise method. But experience shows that this test alone is inadequate to guarantee stability. It is vital to subject apparently satisfactory materials to further kinetic analysis. For example, for a sample of labradorite feldspar which has a broad TL peak centred at about 320°C, the initial rise method gave associated trap depths of 1.6±0.2 eV. However, after storage at 10°C for 25 hours, only 50per thousand of the TL obtained immediately after irradiation was measured. This instability, termed anomalous fading, was found to occur for feldspars in recent lava, and resulted in extremely low ages being determined for dated flows. Anomalous fading was also found in samples of zircon and fluorapatite.