June 2004

Professional Bench/Defining Quality


Prong Setting of Round Brilliants, Part 1: Common Procedure

Knowing methods and techniques for setting round brilliant-cut stones in prongs demonstrates another aspect of quality in your shop


Part 1 of this series reviews a common method of creating bearings and procedures for setting round brilliant stones in prongs. Part 2, pp. 98-100, examines factors that can contribute to prong failure. Part 3, in our July issue, will review and cover details of professional prong setting and a range of problems to avoid.

Bearings

When round brilliant gemstones are set in prongs, they are supported by a bearing (A) and secured by the bearing and prongs. The bearing should provide a uniform seat or platform for the gemstone with no visible gaps or irregularities.

Bench jewelers typically use one of two methods to create a bearing when setting round brilliants in four or six prongs:

The common method used by several bench jewelers who were polled is to use a setting bur the same size or slightly smaller than the gem to be set and burring all prongs at one time (B). Procedures are covered in this article.
Because of the gem size, proportion and other factors, the bench jewelers also reported periodically using a bearing bur and cutting one prong at a time (C). Procedures for this method are covered in the Manufacturing Up Close section beginning on page 102.

Prong Setting Procedure

For this example, we use a setting bur on all prongs simultaneously.

1. Set a 6.4mm round brilliant in a 14k two-tone solitaire by Hoover & Strong. Select a low-speed bur measuring 6.38mm to create the bearing. Prefinish the setting, removing die-striking and other tool marks and making sure prongs are spaced evenly.

Select a low-speed bur the same size or slightly smaller than the gem you are setting.

2. Place the gem on the prongs and view from the top and side. For this setting, I like the girdle to contact the inside of the prongs at the top of the setting.

The prongs should be spread so that when 40% of each prong’s thickness has been removed, the gem will be seated at the desired height. If the prongs need to be moved in, I use chain-nose pliers. If they need to be moved out, I use a dapping punch as shown in this photo.

3. Lubricate the setting bur and begin to cut the bearing, viewing it from the side to ensure the bur is cutting the prongs evenly. (Tool note: Foredom’s series TX Flex Shaft is good for cutting a bearing because it provides full torque at low speeds.)

Make sure the bur cuts all prongs evenly.

4. Remove the flashes or rags of metal created by the burring. Use a knife edge or flat-bottom graver.

Remove all flashes of metal.

5. Place the gemstone in the bearing and check that:

  • The overall depth of the bearing and height of the gem are appropriate.
  • No more than 40% of each prong’s total depth is removed.
At this stage of the setting process, I like the gem’s table to be even with the tops of the prongs.

6. Use chain-nose parallel pliers and a prong pusher to move the prongs over the crown of the gem.

Using parallel pliers, partially bend opposite prongs over the gem and check to make sure it remains level through the partial bending. Then finish the bending using a prong pusher.

7. IMPORTANT: Make sure the prong and crown of the gem are in full contact. Because there is very little possibility of damaging this gem, I use a cup bur to shape the prong tops.

8. Create an identical and evenly rounded top on each prong.
9. The prongs’ contact on the crown is about 30% (D). The top of the prong is close to or slightly below the height of the table when viewed from the side (E).

The solitaire featured in this article was provided by Hoover & Strong, Richmond, VA. For information about the company’s full range of solitaires and other findings, call (804) 794-3700.

– by Mark B. Mann

Illustrations by Lainie Mann
Photographs by Mark B. Mann
© 2004 Visual Communications Inc.

Copyright © 2004 by Bond Communications