Exceedingly Rare and Important Three-Gallon Stoneware Jar with Iron-Oxide and Cobalt Slip Decoration, Stamped "BALTIMORE / UNION STONE WARE / MANUFACTORY," Michael Grub and John Kilmer, Baltimore, MD, circa 1808-1810, ovoid jar with tooled shoulder, semi-squared rim, and arching tab handles, impressed at the shoulder with a large three-gallon capacity mark surrounded by four "BALTIMORE / UNION STONEWARE / MANUFACTORY" maker's marks. Entire surface of jar coated in iron slip and decorated on the maker's marks and at the handles with cobalt slip. Decorated in the "iron-dipped" English style, Baltimore Union pieces were made contemporaneously with related Alexandria, Virginia stoneware produced by Lewis Plum, the master under which John Swann apprenticed. The stamp on this jar predates any maker's marks found on Alexandria or Richmond, VA stoneware, pieces produced by the Webster family in Fayetteville, NC, examples of Samuel Smith, Jr. stoneware from Knoxville, TN, or pieces produced at Abner Landrum's Pottersville Pottery in the Edgefield District of SC, making it the earliest Southern stoneware maker's mark known. This example reveals the beginnings of cobalt slip decoration in Southern-made stoneware with the brushed cobalt spots at the shoulder, the use of blue and brown slip together also linking this work to European-made stoneware. One of five or so pieces bearing this stamp known. Provenance: Recently surfaced in the Midwestern U.S. Most of one handle missing. Losses to opposite handle. Minor surface wear. H 13 3/4".