Made of "Lava" for inside doors. Shown in 1876 Corbin catalog page 595 with key cover.The rose construction is based on patent number 95,899, Oct. 19, 1869 by William Hall assigned to himself & Samuel Peck & Co.For additional information on Lava knobs seeThe Doorknob CollectorNumber 141 Click on each photo below to view additional images and information.