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Use Vector Tightening to Overcome Metal Memory in Prongs

by Douglas Hall - © GIA - 2011
Gemstones that become loose in their settings can cause damage to both the gem and the setting. A regular inspection of jewelry can catch this problem in its early stages, before too much damage is done. Vector tightening prong-set stones is a quick, safe and effective way to secure gemstones.

We'll use a four-prong head with a round brilliant-cut stone as an example. If you try to tighten the stone by simply pushing the prongs in toward the center of the stone -- seemingly the most direct way -- it probably won't be secure. That's because the "memory" of the metal in the prong will cause it to spring back to its original position, and the stone will still be loose. In vector tightening, you move the prongs in two different directions (vectors) to overcome the metal memory.  The prongs end up closer to the center of the stone and hold it tightly. You can use flat or chain-nose pliers to vector tighten, but parallel jaw-pliers work best.

First, gently squeeze the two prongs on the right side (upper and lower right) toward each other. Next, do the same thing with the prongs on the left side. As you squeeze the prongs toward each other, they will "slide" around the contour of the stone. Don't squeeze the prongs too close together -- just reduce the distance between the side prongs by roughly one-third.

At this point, the space between the top two prongs and the bottom two prongs should appear too large, and the space between the two prongs on the right and left sides should appear too small.

Next, squeeze the top two prongs (upper left and upper right) toward each other so they end up with what looks like the original spacing. Repeat with the bottom prongs. The gemstone is now tight, with the prongs evenly spaced around it.

The movement of the prongs in two directions, first toward the sides and then toward the top and bottom, provides tension in the prongs so they are somewhat spring-loaded and hold on to the gemstone securely.



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