Step-By-Step Stone Setting: Gems in Four-Prong Mountings
By Stuller Technical Resources | June 27, 2011
Though a seemingly straight forward task, securing a stone in a four-prong mounting isn’t without its own challenges. Here are tips and techniques for avoiding everything from excessive tool marks to proper seat cutting and shaping prong tips.
- Step #1: Closely inspect the mounting for any material defects, paying particular attention to the prongs.
- Step #2: Check the mounting for stone size then measure the stones to ensure their size match. Note: This is the point when you decide how high or low you will set the stones.
- Step #3: Check the alignment of the prongs and heads within the mounting; straighten the prongs with a pair of chain-nose pliers as necassary. Note: When aligning, grasp the length of the prong, rather than holding it crosswise; this will prevent or minimize tool marks. If you do incur tool marks, use a rubber wheel to remove them.
- Step #4: Pre-polish all surfaces inside the head and surrounding area, then clean the mounting thoroughly.
- Step #5: Measure the stone and select a setting bur slightly smaller than the girdle. Mark the seat location on the prongs with a pair of dividers.
- Step #6: Lubricate the bur and begin cutting the seat in each prong. Note: If you cut each prong separately, rather than all at once, this helps avoid under or over cutting. The seat depth should measure between 30% and 50% of the prong thickness. Make sure the stone sits level in each seat; adjust as necessary. If a seat is cut lower on one prong than the others, the remaining seats will have to be cut lower to match.
- Step #7: Use a knife-edge graver to remove the burs produced from cutting the seats, making them ready for setting.
- Step #8: Pre-bend the prong tips slightly and place the stone into the seat. Tighten the prong tips with a prong pusher. Align and square the stone before the prongs fit snugly. Note: When tightening the tips, work in a cross pattern. Tighten one prong slightly then move to the prong across from it. Work all the prongs in this manner until all the tips fit tight to the crown of the stone. Make sure there is equal space between each prong, and adjust accordingly.
- Step #9: Use an 8/0 saw blade to cut the tips to length. Note: Cut halfway between the table and the girdle line, so that the prong extends halfway up the crown.
- Step #10: Using a 6-cut barrette needle file (with a safety edge to prevent damaging the stone), begin shaping and rounding the prong tips.
- Step #11: Complete the final shaping with a cup bur or beading tool. Make sure the interior opening of the cup bur matches the diameter of the prong tip. Note: If the diameter is too small, a groove will form in the tip.
- Step #12: Use a knife-edge or flat graver to remove the bur from around the prong tip.
- Step #13: Mount a blue rubber wheel in your felx-shaft and remove all tool marks from the prongs and prong tips. Remove all scratches with a small wheel brush and gray star compound.
- Step #14: Buff, clean, and dry the mounting to finish.
- Step #15: Inspect your work: Check the mounting to ensure the stone(s) are still tight, straight, and undamaged.
(mounting shown series 71488)