Many professors at University of Oregon that taught architecture were Louis Khan students from the 40s and 50s. In the 70s we often made site models out of oil based modeling clay in the Khan style.  While working at The Portico Group in the 90s, a workmate of mine, Bill Hacker and I both worked in oil based clay to make site models for projects. We were used to seeing dust gather on the older models for display and were frustrated by the fact that we couldn't easily clean them. We decided to buy a kiln together to make real fired clay models that we could wash easily.  We never did any pieces for work, so I bought out Bill's share of the kiln and have used high heat for art ever since. Most pieces are earthen ware clay bodies usually from Seattle Pottery Supply. Most pieces are fired in an electric kiln at Cone 04 bisque and Cone 6 glaze.