In an issue of <i>CRM</i> concerned with problems of historic preservation involving 20th-century structures, the authors examine panels of thick opaque colored glass used as a building material from 1900 to the 1960s, but no longer made in the United States. Conservation of these panels may require cleaning, repair of joints and minor cracks or chips, removal and reattachment, or replacement in kind, which depends on very limited sources. -- AATA