How to tell Tusayan White Ware Pottery from Asbestos Floor Tile
(when you click on the links, you will access some fairly large jpeg files. They make take a few minutes to download, but if you really want to see the details, here they are, in living color).
1. Examine the temper (non-plastic inclusions) with a microscope or a 10x hand lens with a good light souce: click here
2. Examine the "paint": click here
3. Refire a chip of suspected asbestos floor tile in an electric kiln at 950 C. click here
if it is floor tile, it will become crumbly and will split into lamina then dust. Some inclusions, including the asbestos fibers, may turn light orange. The "clear sand" inclusions will turn bright, opaque white. The "paint" will burn off. It may turn light yellow. Don't worry--there isn't enough asbestos fiber in these things to hurt you.
if it is pottery, it will remain solid. It may break up a little bit, but will not turn to dust with handling. Quartz sand will not change; it will still be clear. Pottery may turn light or dark yellow, or remain white. The paint will burn off if organic paint was used (Tusayan or Little Colorado White Ware); it will turn red if iron-based paint was used (Cibola White Ware).
4. Examine the surface carefully with a microscope. click here
Why is this an issue?
It can be very difficult to tell pottery from old and unfamiliar building materials when conducting a surface survey for archaeological sites. The black lines of tar on the undersurface of floor tiles can look like the black parallel lines of Dogoszhi Black-on-white pottery. The thickness is about right, and with a 10x hand lens and poor lighting, the clear angular inclusions in floor tile can look like sand temper. The sparse asbestos fibers will not be visible without a microscope. Floor tile has fooled many an engineer, who may fear an archaeological site is in the way of his (rarely her) project, so it even has a name in the oral traditions of Southwest pottery classfication: "NTUA Black-on-white," named for the Navajo Tribal Utilities Authority. This types is usually associated with old trading posts, Route 66 gas stations and motels, and historic trash dumps, but may occur as isolated finds.