Setting larger gemstones in four prong type settings is significantly more difficult than setting smaller stones. Any gemstone larger than 10mm in diameter should be considered a larger gemstone for the purpose of our discussion here. Beginners should not attempt setting these larger gemstones until they are very comfortable in setting 8mm stones in similar four prong type settings. There are many reasons why the larger stones are more difficult, one of the easiest to understand is that the metal used to make the larger setting is also larger and therefore more difficult to bend. Another reason is that the manufacturers that make these larger settings aren't making them for beginners, they are made for professional jewelers. This doesn't mean that advanced beginners to setting gemstones can't perfect this skill. It just means that you have more things to consider and to learn when setting larger gemstones.
The first steps in a project like this are to select your materials. We are using 12 mm round, brilliant cut gemstones and a four prong pendant setting as shown at right. The important thing for a relative newcomer to setting gemstones is to purchase a "notched" setting. In the picture at left, you can view the notches in three of the four prongs in this setting. These notches are cast as part of this setting and when received they may contain some casing residue. It is a good idea to use a jeweler's file and clean out the notches by filing each one in turn with either a triangular file or with the edge of a flat file. The notch has to be big enough to accept the "girdle" of the gemstone. The girdle of the gemstone is the widest part of the stone as shown at right.
The second consideration in selecting your materials is to avoid gemstones with a wide or fat girdle. The girdle should be no wider than 1mm and preferably not that wide. Any gemstone with a girdle that is wider than 1mm is not a good candidate for setting by anyone but a professional.
When you have your gemstone and setting ready, position the gemstone withthe table flat on your work surface and position the setting upside down on the work surface as shown at left. Now you need to test whether the setting is properly shaped to hold the gemstone. Lift the setting and position it over the gemstone gently. Do not push down yet, just lightly position the stone. When the setting is ready for your gemstone, the prongs of the setting will be about .5mm smaller than the gemstone itself. (So far, with larger settings, we have not found any setting that was ready right out of the package.) You want the prongs so that they setting will require some pressure to snap into place. That way the stone will be held firmly by the setting. In most cases with larger gemstones, the setting will accommodate a gemstone that is about 1mm larger than the size indicated.
Now that you have tested and, if your settings are like ours, found that the setting won't hold the gemstone firmly as it came out of the package, we are ready to begin
modifying the setting so that it will accommodate our gemstone. The first step is to gently bend each of the four prongs in as shown at left. Do this in very small increments. Notice in the picture that you bend the length of the prong from the supporting circle of the setting to the end of the prong. After bending all four prongs in toward the center slightly, test the stone again by placing the setting on the stone as shown above-right.
When the setting appears that it could accommodate a gemstone about .5 to1mm smaller than your stone, you are ready to set the stone in the setting. This is done by pushing down on the setting as it is positioned above the stone. Use the thumb on your dominant hand. When done properly, you should need to apply firm pressure, but not extreme pressure. It should be about as difficult to push the stone as it would be to slide a gallon jug of milk on your kitchen table but not more difficult. Continue pushing until all four prongs pop into position with the girdle of the stone being held by the notch in each of the prongs. When held in position properly the stone should not easily turn in the setting. If your setting and gemstone do not appear as shown at right, adjust the prongs to remove the stone, adjust the prongs again to fit the stone and start over.
When you get the gemstone in this position the setting and gemstone will look great, but you aren't finished. The stone can be held firmly by the prongs, but over time will still come apart until you finish setting the gemstone by bending the top of each prong in so that it covers a small portion of the gemstone. See the picture at left. You need to bent the portion of the prong from the notch to the end of the prong in toward the center. This will require a little dexterity with your pliers and a little practice. (Please see how to use our gemstone setting pliers to tighten your gemstone in the setting.) If you don't have gemstone setting pliers, use your chain nose or bent chain nose pliers on opposite prongs. On one of the opposite prongs align the jaws of your pliers along the length of the prong. On the opposite prong your pliers will be touching just the outside of the tip of the prong. Squeeze your pliers firmly in this position and it should bend the tip of the prong in. Reposition your pliers to squeeze the opposite prong's tip. Then reposition again to work on the other pair of opposing prongs. When you have done this properly, the stone should be gripped so tightly in the setting that it can't spin or move in any way. If you look at the picture at right closely, you should notice that the tip of each prong is bent inward to cover a small portion of the gemstone.
A few notes for consideration. First, in general, you should not be able to scratch your gemstone with your pliers. You can scratch your pliers with your gemstone, but this won't be a problem. In this process you won't need to worry about scratching your gemstone. Second, you will need to worry about your pliers scratching your setting. If your toolsmanship isn't the best, your pliers may slip as you are squeezing the setting. This will cause a scratch in the setting. If this happens you may need to file the scratch smooth with a jeweler's file. After using the jeweler's file you may need to polish the scratched area. Use your file as little as possible.
Summary on making jewelry with larger gemstones:
Good Luck in setting larger gemstones. It doesn't require any special jewelry tools. It just isn't as easy as setting smaller gemstones, but it is worth it. Remember that you will get better with practice (we did.) If two carat stones are good and four carat stones are great, then what is a 6 carat stone? (A 12mm gemstone, like the aquamarine shown above, is the same size as a 6 carat diamond. It gets noticed!)