Photographed in the former ACR Steelton Yard in August 2004, ACFX 79202 is a good example of a clay slurry service tank car leased to Thiele Kaolin of Sandersville, Georgia.
Kaolinite is a natural occurring mineral often found in a clay form called kaolin. Shipped in either a dry powdered form or mixed with water to form a slurry, one of the primary uses of kaolin is coatings for glossy papers like those found in your favourite magazine. Before it closed down, the St. Marys Paper mill in Sault Ste. Marie produced such high quality papers for the American market, and tank cars of clay slurry would have been common around Sault Ste. Marie.
One interesting thing about the photo above is that all three leased cars visible here are built from different designs and builders. UTLX 300950 to the right was built by and leased from Union Tank Car; ACFX 79202 is built by and leased from ACF Industries while the unknown car to the left was built by Trinity Industries and possibly leased from either GATX, GE Railcar Services (NATX) or Trinity Leasing (TILX).