Rosewood and Ormolu Portico Clock, Late 19th Century

• Ormolu - Ormolu was popular with French craftsmen in the 18th and 19th century for ornamental fittings for furniture, clocks and other decorative items. True ormolu is gilt bronze, that is bronze that has been coated with gold using a mercury amalgam. Due to the health risks associated with using mercury, this method of creating ormolu was discontinued in France in the 1830s. A substitute was developed consisting of about 75% copper and 25% zinc, however it was inferior to the bronze version. It was often lacquered to prevent it tarnishing.
• Rosewood - A dense timber that varies in shade to very light brown to almost black. When rosewood is cut and sanded the colour of the timber will turn black, and after polishing and exposure to daylight, the surface will gradually lighten over time to light brown with black streaks.
  
  The name comes from the odour emanating from the timber when it is planed, sanded or cut.
  
  Rosewood was very popular for use in Victorian furniture in the second half of the 19th century, and at that time most of the rosewood was imported from Brazil. However it also grows in India and Indonesia.
  
  It is used in the sold for chairs and table legs, but for carcase furniture such as side cabinets and bookcases, and for table tops it is always used as a veneer.
• Bezel - On a clock or watch, the bezel is the metal frame into which the watch or clock glass is fitted. In clocks, the bezel may include a hinge and a flange, in effect a door to the face of the clock. In jewellery the bezel is a band of metal with a projecting lip that holds the gemstone in its setting.
• Pendulum - The pendulum was discovered around 1602 by Galileo Galilei, and was adopted for time keeping by the Dutch mathematician and natural philosopher, Christiaan Huygens, who excelled in astronomy, physics, and horology.
  
  The pendulum comprises a metal rod usually of brass or steel with a metal disk, known as a bob, at the end. The movement of the pendulum is driven by weights or a spring, and as a pendulum swings in a regular arc, it was found accuracy could be controlled to within a few seconds a week.
  
  Timekeeping can be adjusted by changing the height of the bob on the rod, making the pendulum either swing slower or faster.
  
  The disadvantage of the pendulum was that changes in temperature also changed the length of the pendulum, interfering with the accuracy of the clock, and so in the 18th century two types of mercurial pendulums were invented which countered the movement in the steel rod.
  
  The pendulum was the world's most accurate timekeeping technology until the invention of the quartz clock, regulated by a quartz crystal, in 1927.

This item has been included into following indexes:

• clocks, type - portico 190
• lyre design - clocks, type 28