power, while in turn the Holy People will absorb the illness and take it away. Afterward, when the sandpainting has served its purpose, it is considered to be toxic, since it has absorbed the illness. For this reason, the painting is destroyed. Because of the sacred nature of the ceremonies, the sandpaintings are begun, finished, used and destroyed within 12 hours. The ceremonies involving sandpaintings are usually done in sequences, termed "chants", lasting a certain number of days depending on the ceremony. At least one fresh, new sandpainting is made for each day. Some Navajo laws and taboos relate to the sandpaintings, and protect their holiness: Women of child-bearing age are not supposed to sing the chants associated with the yeibicheii. This is both because the ceremony has a possibility of injuring an unborn child, and because of a taboo preventing menstruating women from attending. (Some cultures considered menstruation and presence of blood to be powerful spiritual events that had to be restrained, as they represented life forces.) Post-menopausal women are more likely to be chanters or diagnosticians. Authentic sandpaintings are rarely photographed, so as to not disrupt the flow of the ceremony. For many reasons, medicine men will seldom allow outsiders inside a sacred ceremony. Because so many outsiders are curious about sandpainting, some medicine men may create pieces for exhibition purposes only, using reversed colours and variations. To create an authentic sandpainting solely for viewing would be a profane act. The sandpaintings for sale in shops and on the Internet are commercially produced and contain deliberate errors, as the real sandpaintings are considered sacred. The earliest credited instance of traditional Navajo sandpaintings (being rendered in coloured sands as opposed to tapestry or other media) being created in a permanent form for sale, have been traced to between 1945 and 1955. The main credit is generally given to a Navajo Hatałii named Fred Stevens, Jr. (Grey Squirrel), who developed the primary method of "permatizing" for commercial sandpaintings that is still used. Indigenous Australian sandpainting Indigenous Australian art has a history which covers more than 30,000 years, and a wide range of native traditions and styles. These have been studied in recent decades and their complexity has gained increased international recognition. Aboriginal Art covers a wide variety of media, including sandpainting, painting on leaves, wood carving, rock carving, sculpture, and ceremonial clothing, as well as artistic embellishments found on weaponry