Professional Jeweler Archive: Prong Setting Round Brilliants, Part 3: The Results

Knowing how to identify quality features of setting round brilliant-cut stones in prongs demonstrates another aspect of quality in your shop

Professional Setting of Round Brilliants in Prongs

A. The surface of each prong is evenly shaped, equally spaced, symmetrical and proportionate to the size of the gemstone.

B. The height of the prongs ranges between 70% and 80% of the distance between the girdle and table.

C. The amount of prong in contact with the crown of the gemstone is not less than 30% or more than 50% of the total crown angle.

D. The top of the prong is in contact with the crown of the gemstone.

E. The bearing is cut evenly from prong to prong with no visible gaps.

F. No more than 50% of the prongs’ overall depth was removed when the bearing was cut.

G. The prongs were deburred after the bearing was cut.

H. The gemstone is level and not too high or low in the setting.

I. All tool marks from the manufacturing and setting procedures have been removed.

Potential Problems

	These prong angles are wide and steep (A). The top of each prong is too low (B). Seventy percent of the prongs’ overall depth (C) was removed when the bearings were cut. When this gemstone is bumped during normal wear, it will loosen and could dislodge.
	The bearings were cut individually with a 70&Mac251; bearing bur. While the overall angle is satisfactory to accommodate the gem, the bearings were cut at varying depths. When the prongs are held up to a light source, you see space between the gem and the prong. This gem will loosen through normal wear.
	A setting bur was used to cut bearings in the prongs simultaneously. The bearings were cut to 75% of the prongs’ overall depth. One or all of the prongs will break off with normal wear.
	Too much of the top of the prong was filed and/or polished away. This prong’s top will catch, snag, lift and break off.
	The prong wasn’t pushed down completely onto the crown of the gem. It will catch and snag clothing and other material.
	The bearing in each prong was cut individually with a 45&Mac251; bearing bur. The overall angle is too narrow to accommodate gemstones with combined crown and pavilion angles of 70&Mac251; to 75&Mac251;.
	The bearing in each prong was cut individually with a 45&Mac251; bearing bur. A saw blade widened the bearing to accommodate the gem but created a jagged edge and poor contact between the gem and the prong.
	This gem has an irregular girdle and pavilion. When the bearing was prepared, additional metal should have been removed to accommodate the irregularities.
	The prongs are unnecessarily heavy and tall for this size gem.
	The rag of metal created by burring the bearing wasn’t removed before the gem was set.
	The gem was damaged when the prongs were shaped using a cup bur and a file that didn’t have a polished edge.

This series is sponsored in part by Jewelers of America, (800) 223-0673.

– by Mark B. Mann