Petrographic Analysis

4/13/11
Lori Dewson

A bit about the science behind fingerprinting pottery.
 When I was trying to determine the place of origin of the Red Mesa Black on White ware found on the ranch, I knew I needed to locate the source of the materials used to make the pottery. Without access to highly expensive non-destructive processes for analyzing the material, I am left with petrographic analysis of the temper used in the pot.

Because clay easily cracks in the drying and firing processes of making a pot, harder material such as sand is often added to strengthen the vessel. This added material is called temper. To analyze the clay and temper, I have to cut a very thin section of the sherd and grind it down until the minerals are translucent. At this point, the minerals are identified with a polarizing microscope.

Forty of the Red Mesa samples were examined in this way. Twenty-seven samples are constructed of clay and sand found in Chaco Canyon while the rest (though displaying the same Red Mesa design) were constructed from materials local to the ranch. All thirteen samples of the Mesa Verde Black on White were made of materials found locally on or around the ranch.