Radium blanket. This compress was a blanket containing radium, a radioactive metal that disintegrates into radon. In the early 20th century, it was thought that radon was the ultimate health cure. This notion stemmed from the discovery that many of the natural hot springs that were used as health spas were radioactive. Entrepreneurs noticed this and started bottling and selling the spring water as radon water. They later designed household products containing radium, such as this compress, so that consumers could have a supply of radon in the home.