The finest grades of Morocco leather are goat skin, but by the late 19th century other skins often were substituted in practice, particularly sheep skin and split calf skins. The tanning process varied widely, but the traditional tanning material was sumac. The traditional tanning process was skilled and elaborate; according to the application, the preparation either would aim for a carefully smoothed finish, or would bring up the grain in various patterns such as straight-grained, pebble-grained, or in particular, in a bird's-eye pattern. Morocco leather is practically always dyed, traditionally most often red or black, but green, brown or other colors also were available, and in modern times there is no special constraint on color.