WHAT MAKES A BRICK A GOOD BRICK? CINCINNATI: A CITY DIVIDED

In the early 1800’s, an emerging town along the Ohio River named Cincinnati was producing an estimated 8 million bricks per year. The brick business in Cincinnati was quite popular, and bricks were being sold on almost every street corner. This was due to the abundance of clay at shallow depths around the city, making it easy to collect. But making a brick wasn’t as simple as digging some clay out of the ground, shaping it, and baking it. There was a dividing line that separated “good” brick making clay from “bad” brick making clay. Geographically speaking, “good” clay seemed to fall to the east of a small (once large) creek named Mill Creek. In terms of depositional environment, the good clay is presumed to be non-swelling Pleistocene glacial lake clays, while the bad clay is thought to be from more recent fluvial deposits. This good clay was blue, and mostly Illite and Chlorite, with a little kaolinite, and denser than the inferior yellow “bad” clay. This was important when considering the purpose the brick was being made for. The focus of this study was to analyze a group of brick samples dating from the early 1800’s, starting around 1806, with a variety of scientific methods. Also analyzed were some present day samples of clay in order to geographically correlate, with help from previous findings, where the good and bad clays were located. The analyses preformed include X-Ray Diffraction, X-Ray Fluorescence, Infrared Spectroscopy, Scanning Electron Microscopy, and thin section analysis. All of these methods were used together in order to help classify which types of clays composed the bricks, changes in the brick making process over time, and temperatures at which the bricks were fired. Thin section analysis showed that over time, bricks were becoming more uniform in texture and composition. This conclusion was reached by comparing grain size of sand between the samples. The earliest sample is poorly sorted and contains Iron / Manganese nodules. Later bricks were better sorted, pointing to a pre-firing mixing of the material destined to become a brick. Further analysis revealed hematite was present in our samples, indicating a firing temperature of over 800 F. XRD showed strong quartz peaks, which can be attributed to the firing process destroying the clays.