Africa is a vast continent with significant variations in geography and culture. African art can include sculpture, pottery, jewelry, rock painting, textiles, and architecture, among other forms. Much of African art was made from perishable materials, though stone and metal were also common media, and was meant to either be used in religious ceremonies, or was meant to be worn. Most African art is neither labeled nor signed by the artist. Many objects have been discovered accidentally and therefore without any context. Though there is some documentation, in general, ancient Africa lacks a written record as religious and cultural traditions were transmitted orally from one generation to the next, and this can make it difficult for scholars to contextualize, and even confidently date, the ancient art that has been found. One of the most significant problems is illegal excavation and the selling of sensitive objects on the black market—this results in the often-irretrievable loss of important information about a work of art. Similar challenges face art historians studying art from other parts of the world including, but certainly not limited to, the Pacific and the Americas.