It is a disc or plate balanced over another inverted one. The piece is given its basic shape by coiling or molding and then it is finished while turned on the disc. The disc with the vessel in progress is turned only with the hands, which requires a certain amount of balance and skill. One common way to decorate the simplest of ceramic pieces in Oaxaca is called "chorreada" (runny). The pieces are first fired with a clear glaze. Then a second glaze with oxides for color are dabbed on and allowed to run where it may. This double glazing is similar to the production of 19th century Majolica, a pottery form more prominent in central Mexico. The use of raised images on clay items has also been adapted to more traditional vessels, often with the image colored differently from the background. The two best known pottery traditions are "barro negro" and the green-glazed pieces of Santa María Atzompa. Barro negro (black clay) pottery is a style of pottery distinguished by its color, sheen and unique designs, and is most often associated with the town of San Bartolo Coyotepec. The origins of this pottery style extends as far back as the Monte Alban period and for almost all of its history, had been available only in a matte grayish black finish. In the 1950s, a potter named Doña Rosa devised a way to put a black metallic like sheen onto the pottery by polishing it. This look has made the pottery far more popular. While the Doña Rosa's techniques and designs are now widely copied in Oaxaca, the original workshop still exists, with her son Valente Nieto Real still making pieces at seventy years of age. From the 1980s to the present, an artisan named Carlomagno Pedro Martinez has promoted items made this way with barro negro sculptures, which have been exhibited in a number of countries. The town of Santa María Atzompa is known for its jade green-glazed pottery, which has been made the same way for generations. The color comes from the lead monoxide glaze that is applied to it. Atzompa's pottery tradition prior to the Conquest is similar to other settlements in the area, but after the Spanish introduced glazing techniques the green variation was adopted and has changed little since. Up until the mid 20th century, the ware was popular enough to be shipped to all parts of Mexico and even to the United States.