Practical Stone Setting Part 25: Setting an Oval in Prongs

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.

Safety Alert: Burs and other setting tools are extremely sharp and, if used improperly, can cause serious injury. Be sure that your hands are firmly secured and safely protected at all times.

This classic 6-prong oval ring from Stuller has become part of the revised JA Bench test for level one, JA Bench Jeweler Technician. The setting is soldered to pinched split shank and the ring has been polished.

1. The ring is now ready to set the stone. Both the setting and shank are available in a variety of sizes and alloys, such as this example with a 14k white gold head (setting) and 14k yellow gold shank.

Fig. 1. Polished 14k yellow gold ring with six-prong white gold setting and 8 mm x 6 mm oval gemstone

2. When the stone is placed in position and viewed from above, it should be centered with an equal amount of all prongs visible. The stone’s girdle should cover 25–50 percent of the thickness of each prong at the tip. Check and correct the fit of the stone to the head.

Fig. 2. When viewed from above, the stone should cover less than half of each prong.

3. Adjust the spacing and alignment of the prongs with a pair of chain-nose pliers, moving the whole prong, from the base as needed.

Fig. 3. Grab the entire prong with chain-nose pliers to realign it.

4. Carefully set a pair of dividers to the crown of the stone, the distance between the table and girdle of the stone. This will be the same as the depth of the seat.

Fig. 4. Use dividers to measure the crown of the stone.

5. Mark the crown height on the inside of the prongs, from the top. Rest one leg and drag the other across to transfer the measurement to the sides of the prong, very lightly. This line should be so light it is barely visible and will easily polish out. For stones with irregular girdles, cutting above or below the line will be required.

Fig. 5. Transfer the measurement to the prongs.

6. Cut the seat with a 3.5 mm setting bur, which is chosen because this size is too large to pass between prongs but small enough to cut into one prong without cutting the neighboring prong. Hold the flex shaft vertically and very firmly as the bur comes into contact from the inside of the setting. Bur outward on all prongs part way. Stop and check your progress. Make corrections and then bur further until about 45 percent of the metal has been removed. Always leave at least 50 percent of the prong thickness. Use a scrap of wood positioned against the prong to prevent the bur from slipping and cutting around the side of the prong. Make sure the prongs’ seats and walls are identical. De-bur the far side of each prong. Polish all parts, including the interior of the setting.

Fig. 6. Use a piece of wood to protect prongs while burring the seat with a setting bur.

7. Transport the stone to the seat. Ideally, the stone slips into place, making a little contact with each prong as it rests level and evenly on all six seats. Most stones are not symmetrical, and the heights and angles of the seats may need to be modified individually. Make sure the stone’s long axis is correctly aligned with the long axis of the setting, connecting the end two prongs.

Fig. 7. Slide the stone into place; check and adjust the fit.

8. There are many choices of technique when closing the prongs. One way is to rest a pair of chain-nose pliers against the opposite prong and pull inward. Stabilize the tool against your thumb, which rests on the work. Then rock the pliers back and close in the opposite prong, using the leverage gained by the pliers. Close the prongs only part way, until the stone is trapped. Then work around, tightening and closing each pair of opposing prongs. Careful to keep the stone’s axis aligned with the setting, complete the prong closure. The tips of the prongs should make contact with the stone.

Fig. 8. Use a pair of chain-nose pliers to carefully close the prongs.

9. Pre-shape the prong tips with a #4 or #6 cut barrette needle file, with a safe edge. Cut the inside face first at 90 degrees to the crown facets until your fingernail doesn’t catch.