1. The obsidian hydration method. Obsidian, a naturally formed glass, is so constituted chemically that it takes chemicals from its environment at a slow rate. As it does so, the outside layer changes from transparent to translucent or opaque. The depth of the opaque layer, it is hoped, can be used as a measure of the amount of time since the surface was exposed. As many artifacts were made by chipping obsidian to form a sharp edge, this method may reveal the time since an obsidian artifact was made.

2. The thermoluminescence method. The chemical properties of certain minerals change when the minerals are heated to high temperatures. If they are heated again they will glow, and the amount of time they glow upon reheating depends on the amount of time that has elapsed since they were heated originally. As yet the rate has not been accurately calculated, nor is it yet understood what effect different kinds of soils and atmospheres may have on this rate. If the method is proven, it will be invaluable to archaeology since it will afford a way of dating pottery directly on an absolute time scale.

3. The paleomagnetism method. When an object containing particles which can be magnetized is heated, the magnetic particles line up according to the earth’s magnetic field. When the object cools, the particles are trapped in this position. We know that the earth’s magnetic field is changeable, and that at different times it has been oriented in different directions. Work is now in progress to determine how the field has varied through time and how successfully one can date materials such as pottery or hearths which were exposed to high temperatures in the past by the difference between the present magnetic field and that trapped in the object.

Museum of New Mexico Press
Santa Fe 1965

Illustrations by Mary Spencer
and Phyllis Hughes

Transcriber’s Notes