Oaxaca is one of few Mexican states which is characterized by the continuance of its ancestral crafts, which are still used in everyday life. Barro negro is one of several pottery traditions in the state, which also include the glazed green pieces of Santa Maria Atzompa. However, barro negro is one the best known and most identified with the state. It is also one of the most popular and appreciated styles of pottery in Mexico.The origins of this pottery style extends as far back as the Monte Alban period and for almost all of this pottery's history, had been available only in a grayish matte finish. In the 1950s, a potter named Dona Rosa devised a way to put a black metallic like sheen onto the pottery by polishing it before firing. This look has made the pottery far more popular. 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 origins of barro negro pottery extend over centuries, with examples of it found at a number of archeological sites, fashioned mostly into jars and other utilitarian items. It has remained a traditional crafts of the Zapotecs and Mixtecs of the Central Valleys area to the present day. Originally barro negro pottery was matte and grayish. In this form, the pottery is very sturdy, allowing it to be hit without breaking. In the 1950s, a woman by the name of Dona Rosa Real discovered that she could change the color and texture of the pieces by polishing the clay pieces and firing them at a slightly lower temperature. Just before the formed clay piece is completely dry, it is polished with a quartz stone to compress the surface. After firing, the piece emerges a shiny black instead of a dull gray. This innovation makes the pieces more breakable, but it has made the pottery far more popular with Mexican folk art collectors, including Nelson Rockefeller, who promoted it in the United States. The popularity stems from the look, rather than wearability, so many pieces are produced now for decorative purposes rather than utilitarian. Dona Rosa died in 1980, but the tradition of making the pottery is being carried on by Dona Rosa's daughter and grandchildren who stage demonstrations for tourists in their local potters' workshop. The workshop is still in the family home, where shelves and shelves of shiny black pieces for sale line the inner courtyard. Despite being the origin of black polished clay, pieces at this workshop are much cheaper than in other parts of Mexico."