Photo courtesy of Penn Big Bed Slate.

Slate from Penn Big Bed Slate Co. Inc., Slatington, Pa., stands ready to ship.

Photo courtesy of Preservation Technology Associates Inc., Boston.

This chapel, built during the 1870s at Wesleyan University, Middletown, Conn., features North Country black slate, which was substituted for the original Monson slate. The red slate is from New York.

Photo courtesy of Preservation Technology Associates Inc., Boston.

This 1870s house in Cambridge, Mass., was designed by the same architects who designed Harvard University’s Memorial Hall. Black slate and unfading green were used to restore the roof system’s original design.

This Web exclusive information is a supplement to A decade of change.