Enamel is a decoration technique in which a glass of certain composition is fused to the surrounding or under laying metal. Although the exact origins are unknown, the art of enamelling has been practiced since ancient times. The favor of adorning jewelry with bright colors has always existed and the use of glass created colors which nature – in the form of gemstones – could not provide for in ancient times. Excavations on Cyprus – in the Mediterranean – in the 1950’s brought cloisonné enameled jewelry to the surface which dates from the 13th and 11th century BC. These are, to date, the earliest enameled items found in this particular technique.
Although the ancient Egyptians decorated their royal artifacts with an ascendancy of colored gemstones, glass and faience, this was not an enameling technique. Rather a form of mosaic. Early Roman enamels were also of this type where they used pieces of multicolored glass (“millefiori”) and placed them in a predestined pattern. The gaps in between were filled with a glass powder which, after heating, fused the millefiori smalti together. Though this is similar to enameling, the glass did not fuse to the metals. It was only later that they started to place the smalti in a type of tube setting and then punching the metal over the glass, followed by heating at the appropriate temperatures which caused a fusion to the surrounding metal, that we can speak of a true enamel.
During the Byzantium era cloisonné enamel flourished in the Eastern Roman Empire as well as in many Celtic areas (as Gaul and in Britain). This technique has been known for over two millenniums and it could well have spread over Europe during the migration period which preluded the middle ages.

Art Nouveau (the term comes from French and it means New Art) is an art style which was mainly manifested in visual arts, design and architecture in the late 19th century and the early 20th century (1890 – 1914), almost in the same time in most of the cultures and European countries , but also in North America.

This style was spread pretty fast throughout Europe thanks to photo-illustrated art magazines and international exhibitions. Its name differed according to each country, so it was called “Modernisme” in Catalonia, “Liberty” in Italy, “Jugendstil” in Germany, “Secession” in Vienna or Prague.
Here are some examples of modern silver jewelry inspired by Art Nouveau:

Turquoise is one of the oldest known gems..

The name “Turquoise” may have come from the word Turquie, French for Turkey, because of the early belief that the mineral came from that country (the turquoise most likely came from the Alimersai Mountains in Persia (now Iran) or the Sinai Peninsula in Egypt, two of the world's oldest known turquoise mining areas.)

Another possibility could be the name came from the French description of the gemstone, "pierre turquin" meaning dark blue stone.

Many thousands of years ago, long before written history, human beings probably discovered the first pearl while searching the seashore for food. Throughout history, the pearl, with its warm inner glow and shimmering iridescence, has been one of the most highly prized and sought-after gems. Countless references to the pearl can be found in the religions and mythology of cultures from the earliest times. The ancient Egyptians prized pearls so much they were buried with them. Cleopatra reportedly dissolved a single pearl in a glass of wine and drank it, simply to win a wager with Mark Antony that she could consume the wealth of an entire nation in just one meal.

In ancient Rome, pearls were considered the ultimate symbol of wealth and social standing. The Greeks held the pearl in high esteem for both its unrivaled beauty and its association with love and marriage. During the Dark Ages, while fair maidens of nobility cherished delicate pearl necklaces, gallant knights often wore pearls into battle. They believed the magic of these lustrous gems would protect them from harm. The Renaissance saw the royal courts of Europe awash in pearls. Because pearls were so highly regarded, a number of European countries actually passed laws forbidding anyone but the nobility to wear them.

During the European expansion into the New World, the discovery of pearls in Central American waters added to the wealth of Europe. Unfortunately, greed and lust for the sea-grown gems resulted in the depletion of virtually all the American pearl oyster populations by the 17th century. Until the early 1900's, natural pearls were accessible only to the rich and famous. In 1916, famed French jeweler Jacques Cartier bought his landmark store on New York's famous Fifth Avenue -- by trading two pearl necklaces for the valuable property.

But today, with the advent of pearl cultivation, pearls are available and affordable to all.