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Diamonds are chains of carbon. Carbon is one of the most common substances on the planet. In one form it is simple graphite, used in pencils, but in its crystallized form, it takes an altogether different appearance as diamond. On the scale used by mineralogists to measure the hardness of minerals, diamonds rate ten on a scale of one to ten. Diamonds are measured in carats, the standard unit of measurement for gemstones. One carat is roughly equal to one-fifth of a gram. The carat can be further divided into points based on a scale of 100. One of the reasons diamonds are so prized is because the light they absorb is reflected directly back outward, if the stone has been properly cut. The unusual crystal structure of the gem allows this high degree of refractability. Because of their structure, diamonds are also excellent conductors of electrical current.

The Eighteenth to the Twentieth Centuries

In the late 18th cent. the fashion for decorative buttons, watches, and snuff boxes almost superseded the wearing of jewelry. After 1800 the bracelet, which had dwindled (c.1500) in importance with the ruffed and cuffed long sleeve, was again in favor. The 19th cent. also saw the revival of the cameo and the introduction of the watch and chain and sets of jewelry. With the introduction of factory-made ornaments, artistry of workmanship declined. In the 20th cent. platinum became popular for settings. Costume jewelry, which followed the rapidly changing fashions in dress, was introduced (by Gabrielle Chanel), as was the wristwatch. There was a renewal of enthusiasm for handwrought pieces during the craft revival of the 1960s in the United States.

Diamonds are a finite resource. The fate of Indian diamonds is a good example of what the future might hold for the South African diamond-mining industry. From the first discovery of the gems in India until relatively recently, it is thought that over 12 million carats originated from India. By the mid-20th century, the resources were nearly depleted, and India was producing only about 100 carats annually. Diamonds will continue to be used in industry and high-technology enterprises, but synthetically produced facsimiles—first manufactured in 1953—may accomplish some of the tasks originally the exclusive province of the real stone. These "manufactured" gems have the same properties of hardness and durability, and while they will never be as popular as the real diamond for adomment purposes, they are well suited for industrial applications.

The Middle Ages to the Seventeenth Century

Jewelry of the Middle Ages was massive; large brooches and girdles predominated. Amber was worn as a protection against evil spirits. After 1300 glass beads were used. The Renaissance brought a transformation in the art of the jeweler; noted artists and architects often designed or even rendered pieces of jewelry. Jewelry was splendid with enamel and precious stones; heavy gold link chains, jeweled collars, and the necklace with pendant were worn by both men and women. Jewelry, worn to excess, became overcrowded with stones, to the neglect of the design and setting. By the late 17th cent. the goldsmith and enameler gave way before the lapidary and mounter. A process of making imitation pearls was first discovered in 1680; thereafter, ropes of pearls became highly popular for women.

4 The viewfinder lens is a specialized lens that is manufactured using the same methods as a camera lens. The viewfinder also is made of optical glass, plastic, or glass/plastic combinations. All but the simplest viewfinders contain reticles that illuminate a frame and other information on the eyelens to help the photographer frame the picture. An in-line mirror has specialized coatings for color splitting; as many as 17 coatings may be added to the mirror to correct and modify its reflective properties.

Quality assurance and quality control practices are a matter of course among camera manufacturers. All departments from manufacturing to shipping have their own quality assurance procedures, and companywide quality assurance is also overseen by a separate division or department. The overseeing quality assurance divisions use statistical methods to monitor aspects of product quality such as camera function, performance, consistency, and precision. They also guide the flow of one assembly system into another and provide corrective measures if problems arise.