Print, Photographic

Black and white photographic print mounted on fabric depicting the Inyo Mountains in California.
Caption reads: Photograph 1
The knowledge of the microstructure of porcelain and experiments with the use of sillimanite to replace quartz, naturally brought about the question of a cheaper source for sillimanite than could be secured by synthetic preparation from a mixture of clay and pure alumina.
The natural forms of sillimanite are cyanite, andalusite and sillimanite. The first two forms convert to sillimanite upon heating, but they have never been found in commercial quantities in nature until recently when Dr. J. A. Jeffery discovered a deposit of the natural mineral andalusite, which is located in the Inyo Range, California.
This photograph shows this range. At the right is a cliff which is large composed of andalusite, and which is now regularly being mined and used for our spark plug porcelains.