This is a geochemical method of determining absolute time of an artifact made of obsidian (volcanic glass) up to 50kya. Volcanic glass can form very sharp edges and is used in making tools. Water from the surrounding environment begins to soak into the tool, and over time a band/rim will form. In theory, the thicker the band the older the object, which gives archaeologist a sense of time for some tools. However, an issue that comes up with this method, is that it cannot take into account people recycling tools, and re-wearing them down. In addition, the saturation of a toll is specific to its environment, and cannot be compared with another tool that appeared in a different environment.