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Prong Setting 101

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Prong Setting

Prong setting is by far the easiest method of setting stones. However, it still takes practice and a working knowledge of tools and procedures to master.
Ask 5 jewelers what method is used to prong set a stone and you will probably get 5 different answers. In these examples I will show you what methods work best for me.
In the first example, I will be setting a pear shaped star cut blue topaz in a standard 4 prong double gallery basket head.

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Checking the fit

The first step in setting this stone is to check the fit in the mounting. You want to make sure the mounting will fit the stone. The stone should either rest just on the inside top of the prongs or just slightly down the prongs a bit.
If the mounting is just slightly too big, the prongs can be bent inward slightly. If the mounting is just slightly too small, the prongs can be bent outward slightly. In this case, the stone fits perfectly in the mounting.

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In most cases, I like to set the stone as low as possible in the mounting without the culet poking through the bottom. I think it looks better and also it makes for a stronger setting job. The shorter the prongs, the harder they are to bend out of place; however, star cut stones are usually cut with a 65 to 80% depth, so I will have to set this stone a little higher than normal.
Marking the prongs

The prongs can be marked for burring in one of three ways:
A. By eye
B. With a fine tipped permanent marking pen
C. Scribe lines made with a pair of dividers (provided the prongs are all the same length)

On round stones, marking the prongs is usually not necessary because the girdle of most round stones is fairly even all the way around the stone. In this case, the stones girdle angles upwards about 30 degrees near the point of the stone, so I will mark the location of the prongs where I will cut the seat.

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Cutting the seat

Cutting the seat for the stone can also be accomplished in several different ways.
With a file
With a 90 degree bearing bur
With a setting bur
I prefer to use a 90 degree bur in most cases. If done properly, more metal will be left on the prong tips - resulting in a longer wearing piece.

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The trick to cutting the prongs on large stones without the bur running around the prong is to rest the prong on the bench block. If the bur does try to run, the block will prevent it from running around the prong.
I like to cut a notch in the prong to about 40% of it thickness. If the stone has a thick girdle, you will need to walk the bur up and down the prong just slightly so that when you set the stone, the prong will wrap around the girdle instead of pinching it; which would result in a gap between the prong and stone.
With this stone, I have to angle the cuts of the two top prongs due to the angle of the girdle.

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After the seat is cut in each prong, the burs that were created while cutting need to be shaved off with a graver or scraper.
Now is also the best time to polish the seat and inside the setting. It is very difficult to polish after the stone is set.

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Setting the stone

The stone should fit snugly in the seat before bending the prongs over the girdle. Test fit the stone. It should fit snugly and almost snap into the seat. If not, remove the stone and bend each prong inward slightly. If the stone wont go into the seat, then bend each prong out slightly.
I like to use the Wesgem parallel setting pliers on large stones. The jaws can be adjusted open and closed by a screw and the amount of throw is only about a millimeter or two. Each prong can be bent over an exact amount so the risk of breaking the stone is reduced. Also if the plier slips off the prong, the jaws of the plier wont smash into the stone and break it. These pliers have a lever action, so the amount of force needed to bend the prongs is less than it would be with conventional pliers.
Rest one jaw on the top of the prong on one side and the other jaw down near the top gallery of the opposite side. Squeeze the prong down slowly until it almost makes contact with the crown of the stone. Repeat this on the opposite prong, then repeat this on the two remaining prongs. Make sure the stone stays level in the seat as you are bending the prongs over. If you happen to bend one prong down too far, stop and lift the prong up with a prong lifter or nail clippers.

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Once the prongs are almost down flat on the crown facets of the stone, take your pliers and rest one jaw on the bottom of the basket under the prong and the other jaw on the top of the prong. Bend each prong down in the same order as you did above; going to each opposite side until all the prongs are down on the stone. There should be no gaps between the seat, girdle, crown or prong tip.

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If you have a springy prong that just doesn't want to go down, a neat trick to get it flat on the stone is to: rest one side of your plier on the prong tip and the other side on the prong right next to it near the top gallery. Bend the prong toward the other prong. Then rest your plier on the opposite side of the same prong and bend it toward the opposite prong closest to it until the prong is straight again. This will usually take care of the most stubborn prongs.

Finishing the prongs

The prongs can be finished off in a couple of different ways. The objective is to make the prong tips the same size and smooth where they won't snag clothing. You can either use a needle file or a cup bur.
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If using a needle file make sure it has a "safe" edge on it. I use a flat file that has been polished smooth on one side. The polished side is the side that rests on top of the stone while filing the prong. The prong cane be finished off in a couple of ways. The traditional method is to simply round the prong tip. Another method that is used on antique or estate style jewelry is to file the prong tip to a tapered point at the end and then file the top of the tip flat down on the crown of the stone.
I prefer to use a cup bur because it is faster than a file and I like the rounded look of the tip. I believe the prong wears better if it is rounded off rather than tapered.

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If any flashing burs remain after filing or burring the prong, you can take a flat graver and cut them away. Polish and clean.

Finished Setting

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