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"An Overview" |
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Proper Prong Setting This drawing illustrates the important features apparent when a round brilliant stone is set properly into a die-struck head. The surface of each prong is smooth, rounded and polished. The height of the prong is between 70% and 80% of the height of the table (arrow1). Each prong is bent and securely formed over the stone's crown so the metal of the prong is flat and even against the crown (arrow 2). Each prong has an angle cut into it to accommodate and conform to the stone's shape, providing a secure seat on which the stone can rest evenly (arrow 3). The "heel" of each prong is no less than 50% of the prong's original thickness, providing structural strength for years of trouble-free wear (arrow 4). |
Potential Prong Problems
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Prong Thin at Heel If the "heel" of a prong is thin (less than 50% of the prong's original thickness), it may catch, bend and break easily. A stone set with a thin prong will never stay tight. Thin prongs may result from normal wear or errors in workmanship. |
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Prong Thin at Top If the top of a prong is this thin, it will catch, bend and eventually break off, resulting in loss of the stone. Prongs that are thin at the top are caused by extended normal wear or errors in workmanship. |
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Hooked Prongs If the prong is shaped with a hook like this, the stone will seem tightly set at first but will loosen within a short time. This type of prong will break, resulting in a lost stone. Hooked prongs are caused by an error in workmanship. |
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Prong's Lacking "Bearing" "Bearing" refers to the angle cut into a prong to accommodate and conform to the stone's shape; the angle provides a secure resting place for the stone. A prong with no bearing gives little or no support for the stone, which will tip or become loose. Lack of bearing results from an error in workmanship. |
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Incorrect Prong Angle Prongs normally have an angle of 70% to 80%. This prong is angled out too steeply; normal wear and tear may cause the prong to bend farther outward, resulting in a loosened or lost stone. Incorrect prong angle is the result of an error in workmanship. |
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Prong To Low There should be between 33% and 50% contact between the surface of the top of the prong and the crown of the stone. This prong is too low, so there is insufficient contact with the stone. When the stone is bumped during normal wear, prongs that are too low will bend back and the stone will be lost. With more contact area, the stone may loosen but will not fall out. The combination of incorrect prong angle and low prongs will always result in a lost stone. |
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Upright Prongs Upright prongs cause uptight customers. If the top of the prong is shaped like this, it will catch on fibers and clothing (a common cause of ruined pantyhose) and eventually bend farther back until the stone loosens or falls out. Upright prongs are caused by an error in workmanship. |
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Prong Cut With A Saw Cutting prongs with a saw is a fast way to set a stone and an even faster way to lose it. Cutting with a saw weakens prongs. |
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