all original and historically important late 1860's exterior chicago residential italianate rowhouse window hood keystone designed and manufactured by the frear artificial stone mfg. co., chicago, ills. the keystone is unique in that its comprised of artificial stone (also termed "cast" or "concrete" stone), which is a synthetic product that was used mainly during the 18th and 19th centuries to imitate natural building stones. an aggregate of water, natural cement, lime, sand, and/or various binding agents, the concrete mixtures could be incorporated in construction as molded shapes and intricate decorative elements or as plain blocks. with various basic mixtures, production processes, and methods of finishing the cast stone could be employed to imitate a wide array of natural materials. a light cement matrix with crushed marble could replicate limestone, while a mix of marble and small amounts of melting slag would give the effect of white granite; the addition of masonry pigments could imitate variegated sandstone. some of the earliest formulas were created in britain, with coade stone produced from 1769-1833, and a patent process in 1844 of a formula by frederick ransome. additionally, coignet stone and frear stone (created by chicagoan george frear) were patented several years prior to the great fire of chicago. the "frear patent" window or door hood keystone remains largely intact with a nicely weathered surface patina. discoloration and surface cracks evident. measures 16 x 9.5 x 21 inches