Practical Stone Setting, Part VII: Small 3-Prong Side Settings

Here is a standard three-stone ring in gold, with settings for a pear-shaped center stone and two small side diamonds in three-prong settings. The ring is a typical commercial mounting from Stuller that comes ready for the jeweler to set using either customers’ stones or stock gems.

After the ring has been polished, prepare to set the two side stones first, while there is still access, and then set the pear-shaped center. This project explains how to set small diamonds in three-prong side settings; for instructions on setting the pear, see “Practical Stone Setting, Part VIII: Pear Setting” in next month’s issue of JCK.

In this cast mounting, the two side settings each have two prongs up against the base of the center stone and a single prong coming from farther down the shank. While most prong settings can be modified to accommodate a range of sizes, there is very little room for alteration of the size of these small settings. Note that each side setting is angled slightly away from the center.
Generally, when setting two or more identical stones in identical settings, it is wise to work alternately on each, step by step. This practice is more efficient and also results in greater accuracy.
File the tops of the prongs to make them all level and even. Put a minute amount of sticky wax on the inside edge of the prongs. Because the prongs are just about vertical, the best way to judge if the size is correct is to place the stone on top and view it from above. The perimeter of the stone should cover about half of each prong tip. This will ensure that the seat where the stone rests goes halfway into the prongs—the correct amount. For example, a 1.75-mm diamond (2 points) covers about half of each prong when placed on top.
The prongs now are approximately where they will be when the stone is set. However, in order to cut the seats, the single prong must be moved out to allow the bur to enter. This prong will be returned to its original position over the stone during setting. To move the prong, use either a scribe inserted in the center of the setting or grab the prong with a pair of chain nose pliers and move it outward at an angle, making the opening too large for the stone. Repeat on the other side.
Select a bur that is the same shape as the stone, but slightly smaller. In this case, a Hart bur matches the profile of the stone and 1.6 mm is about right for the size. When setting, it is common to start smaller. This way the opening will be slightly undersized and, if necessary, can be enlarged by burring a bit further at any time.
With the ring held firmly in a ring clamp or engraver’s block, lubricate the bur. Hold the work firmly. Brace your hands and stabilize your fingers on the ring clamp and ring. With the bur spinning at a slow speed and with the greatest control, insert the bur at an angle coming over the center of the ring, making contact with the two inner prongs.
Cut slowly into both inner prongs. As you cut, slowly tilt the bur back over the center of the setting, where the bur continues cutting into the two inside prongs.
Continue cutting, and, keeping the bur level, move it outward into the single prong as you begin to cut the third seat. Check the seats in all three prongs for accuracy. The seats should all be at the same height and level, and they should be the same depth into each prong. Use a file to clean up any rags of metal from burring.
With the gem held at the end of a sticky wax “diamond magnet,” insert the stone at an angle, sliding it into the seats of the two inner prongs first.
Continue to insert the diamond. As it settles into the inner seats, rock it downward into the seat in the single prong. Ideally, if the opening is the right size and the seats are in the right places, the stone will barely slide into place and might even require a small amount of pressure.
At this point, the stone should be in its final position. Check to make sure it is level in the setting, which is tilted out a few degrees from the center stone. Be sure both stones are set at the same angle in relation to the center of the ring.
With the prongs left long, there is greater leverage, which makes the job of setting easier. Close in the outer prong using a steel pusher with a ball handle. Begin by pushing directly sideways, forcing the prong over the stone. Continue, raising the angle of force as needed, until the prong is in full contact. Check the other prongs and, if needed, push them further over the top of the stone as well.
After you have checked to make sure the prongs are all in full contact, check to see that they’re evenly spaced around the stone. Use a pusher or chain nose pliers to move the prongs. Remove the excess from the prongs with a pair of flush cutting nippers (side, diagonal, or end cutters). Leave the metal slightly higher than the table. [Note: Be sure to wear eye protection whenever cutting prongs.]
Use either fine-cut needle files or a cup bur to shape and finish the prongs into perfect hemispherical tips. Select a cup bur of about the same size as the prongs and slowly carve the desired shape. Just jamming it onto the metal does not work as well as using it to “scrape” from different angles. Be careful not to let the bur gouge the prong.
Finally, buff and polish the prongs. Use an abrasive compound like tripoli or fine pumice wheels to clean up surface imperfections, then polish with rouge.

The procedures in this article are standard practices for bench jewelers at this time. If not executed properly, however, they can cause harm. Neither the author nor publisher is responsible for injuries, losses, or damage that may result from the use or misuse of this information.

JCK

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