Portico Clock: French make 8-days striking mantel clock. The Portico mantel clock was introduced during the Empire period. These clocks are very decorative and also known to be precision clock as it uses temperature compensated pendulum. This unique pendulum is constructed using alternate rods of Steel and Brass connected by cross pieces at the top and bottom, known as gridiron pendulum, hence the pendulum length does not vary by changes in the temperature.