Although painted iron dials are sometimes found in early Gothic clocks, brass was the principal material in general use from the late 16th to the later years of the 18th century, when enamel or iron dials began to appear. Before the Industrial Revolution, when it became possible to produce sheet brass of even thickness in a rolling mill, brass dials were cut from sheet metal which had been cast and reduced to the required gauge by beating with trip hammers operated by water power.