Gemstone Floral Brooch with Onyx and Rolled Gold Frame

• Onyx - Onyx is a form of agate, used from antiquity and popular again in the 1920s and 30s. European onyx is generally green, but can be many other colours, and can contain bands of black and/or white.
  
  This multicoloured stone is widely used for table tops, lamp bases and in jewellery. Some types of onyx are also used for cameos of which the upper white layer is cut away to reveal the colour beneath.
• Rolled Gold - A type of gold plating devloped in the early 19th century, similar to Sheffield plating of silver, where the the gold is fused under pressure and heat to a base metal, usually brass, and then rolled into sheets of the required thickness.
  
  The thickness of the gold plate can vary. In Britain the thickness of the gold is measured in microns. A micron is one-thousandth of a millimetre and 20 microns of gold is considered good quality. In the USA a differnt method is used that takes account of the total weight of the object.
  
  Also, the purity of the gold, measured in carats can vary, with 24 carat being the purest. The gold in most rolled gold objects will be between 9 and 14 carats.
  
  There are other chemical and electroplating methods of applying gold plate to a base metal, but rolled gold is considered a superior plate to a "gold plated" object.
  
  Depending on the country and date of manufacture, the object may be stamped "Rolled Gold" or similar, but if there is any doubt as to whether an object is solid gold, or some type of gold plating, it is preferable to have it tested by a jeweller.
• Coral - Coral used in jewellery. Coral is a material that is commonly used in jewellery making. It is made up of the skeletons of tiny marine animals called coral polyps. There are many species of coral, but only one group, Corallium, is suitable for carving, and thus can be used in jewellery manufacture. These have a deep red or pink orange skeleton and are known as "noble coral" or "precious coral".

This item has been included into following indexes:

• brooches, floral design - floral design, gold mounted 914
• brooches, gold - gold with pearls 957