Gold Karat
Gold's softness and malleability make it a wonderful metal to work with when creating virtually any design in jewelry. But this softness can be a drawback as well. To make it stronger and more durable, gold is usually alloyed, or mixed, with other metals such as copper or silver. The higher a metal's percentage of gold content, the softer and more yellow the jewelry piece. The karat weight system used to measure gold in a piece is the same for all hues, including white and yellow gold.

The word “carat” is Arabic, meaning “bean seed.” This is because historically seeds were used to measure weights of gold and precious stones. In the United States, “karat” with a “k” is used to measure gold's purity, while “carat” with a “c” is used in measuring a gemstone's size. The karat mark of gold represents the percentage of pure gold to alloy.

In order to determine the karat weight of a specific item, simply look for the quality mark. Jewelry items will bear the stamp of their karatage based upon the United States or European system of marking. The United States system designates pieces by their karats—24K, 18K, 14K, 10K, etc. The European system designates pieces by their percentage of gold content. For instance, 10K gold is marked “417,” denoting 41.7% gold; 14K is marked “585,” denoting 58.5% gold; and 18K is marked “750,” denoting 75% gold; etc.

Yellow Gold
By far the most common color of gold used in jewelry, yellow gold is gold in its natural shade. Yellow gold is usually alloyed with copper and silver to increase the strength of the metal. How yellow the metal is depends upon the content of gold. A 14-karat piece of jewelry will have a brighter yellow hue than a 10-karat piece. Likewise, an 18-karat piece of jewelry will have a deeper yellow than 14-karat gold, and so on.

Agate
Found all over the world, agate has been creatively striped by nature. It is a type of chalcedony quartz that forms in concentric layers of colors and textures. Each individual agate forms by filling a cavity in a host rock. As a result, agate often is found as a round nodule with concentric bands like the rings of a tree trunk. Tiny quartz crystals called drusy (sometimes spelled as druzy) often form within the stone, adding to its beauty and uniqueness. Agate is a hard stone, within the range of 7.0-9.0 on the Mohs Scale.

In 1497, the mining of agate in the Nahe River valley in Germany gave rise to the cutting center of Idar-Oberstein. When the Nahe agate deposit was exhausted in the nineteenth century, Idar cutters started to develop the agate deposits of Brazil, discovering Brazil's rich deposits of many other gemstones. A famous collection of two to four thousand agate bowls, accumulated by Mithradates, King of Pontus, shows the popularity of agate at the time. Agate bowls were also popular in the Byzantine Empire. Collecting agate bowls became common among European royalty during the Renaissance and many museums in Europe, including the Louvre, have spectacular examples.

Although the small town of Idar-Oberstein is still known for the finest agate carving in the world, today Idar imports a huge range of other gem materials from around the world for cutting and carving in Germany. Cameo master carvers, modern lapidary artists and rough dealers flourish there, exporting their latest gem creations. It is an entire industry that grew from the desire for agate products during the Renaissance.

Agate was highly valued as a talisman or amulet in ancient times. It was said to quench thirst and protect from fevers. Persian magicians used agate to divert storms. Today, some believe that agate is a powerful emotional healer and helps people discern the truth.

Earring Back Types

Butterfly Back: A double looped piece resembling a butterfly that fits over a post. Variations on this design are called push back clasps. The basic post and butterfly back are usually used for stud earrings and lighter weight drop earrings.

Hinged Snap Backs: This clasp features a hinged post that snaps into a groove on the back of the earring. It is commonly found on hoops. Sometimes the hinged post is curved to provide more room to fit around the ear, sometimes called a saddleback.

Hook Backs: This earring backing is simply a long, bent post that fits through the piercing. Hooks have several variations, most notably the shepherd's hook and the French hook. While thin wire hooks reduce the weight of long earrings, making them more comfortable, they aren't as secure as other clasp styles.

Lever Back: A hinged lever snaps shut against the curved post to form a closed loop around the ear lobe. This clasp is very secure and good for large or medium sized styles that drop just below the ear.

Omega: Also called French clips, this clasp has a straight post and a looped lever. The hinged lever closes around the post and is held against the ear with pressure. The omega clasp is the most secure clasp, especially for the larger, heavier earrings.

Screw back: This backing is a slight variation of the standard post and butterfly nut back. Instead of pushing on the back, the nut twists onto the threaded post. A screw back post design is often preferred for expensive diamond stud earrings that require increased security.