Tightening Prongs on a Setting

Q: How do you get the prongs of a Tiffany head to hold a stone tightly? And how can you clean up prongs without catching and distorting them?

A: Vector tightening is the best way to tighten a prebent prong to a stone. It’s also generally good for tightening already set stones that have become loosened in wear. Gold, silver, and even platinum are a bit springy. This means that if you bend a prong tight and let go, it springs back, leaving the stone loose. Attempting to force it tighter can break the stone. You’ve doubtless seen the same thing in closing jump rings, which, if closed straight together, spring back a little, leaving a gap. If one moves the ends side to side while closing, the gap stays closed. The same idea is used in vector tightening. Instead of squeezing opposing prongs straight together toward the center of the stone, you squeeze adjacent prongs slightly together. This, of course, puts them skewed sideways out of position, but the springback occurs to the side now. The prongs are moved slightly toward the stone at the same time, but in this case they stay there.

If you number a four-prong setting as prongs 1 through 4, you’d squeeze prongs 1 and 2 slightly together, then 3 and 4. Now go back and do the same again with 1 and 4, and then 2 and 3. At this point each prong has been bent slightly to one side, and then equally back to the other side. So now they again line up square to the stone and straight up and down. Obviously, you do this whole thing carefully, and gently, a little at a time. After all, you don’t want to end up with distortion and rippled metal along the sides of the prongs. And as you work, be careful to avoid putting plier marks in parts of the prongs which you cannot clean up again.

With larger heads, parallel jaw pliers are useful. And of course, if you are using this technique to set a stone, you can initially bend the prongs straight in toward the stone to get them most of the way to where they need to be. The vector technique is the last part, where you snug everything up and get them tight. This concept of prebending the prong tips avoids a great deal of the accidental breakage of stones in setting, especially with larger or fancy-shape stones, as the hard bending is done without the stone in the head. And vector tightening allows you to gently tighten a prong to where it needs to be without pressing the prong straight into the stone. This avoids much breakage, as well as working better.

One more thing to keep in mind when cutting seats in prongs that are to be bent directly over the stone instead of prebent, as is often the case with smaller round stones in the standard die-struck heads, is that any metal wire, such as a prong, when it’s bent, compresses on the inside of the bend and stretches on the outside. That compression effect causes the inside surface to bulge slightly. This means that the inner surface of a prong you are bending will tend to contact the stone slightly before the outer edge. That makes it hard to get it to look tight, and if you mistakenly think it’s still loose and press down more, you can chip the stone. It’s for this reason that slightly hollowing out the inner surface of each prong with a small ball burr tends to give good results in some cases. Tiny stones, of course, don’t usually need this. But with heavier prongs it’s a good idea.

As for the problem of catching prongs with burrs; use the burrs at higher speeds, and they will catch less. Use them with Rio’s Burr Life or similar burr lubricant (beeswax, oil of wintergreen, even saliva), and you’ll smooth out the cutting as well. Be especially careful not to catch the “upstream” edge of the prong, as that’s what causes it to grab. A larger burr will also make this easier to avoid. If you still have trouble, then use the finer tooth Busch style burr, instead of high-speed ones.

Setting stones is a rewarding skill. But it’s not a simple or quickly learned one. Doing it well with all sorts of stones and setting styles is a highly skilled profession in its own right. So don’t be discouraged if you find that it takes more than one or two tries to learn. And always remember that fine method of stone setting, the “three by five” method. For beginners and those not completely sure of their skills, especially with fine expensive stones, it’s the method that usually produces the best results. This involves putting your job in a three by five inch mailing box, and sending it to an expert stone-setter. The bill you get is usually well worth the reduction in risk to the stone, and the increase in the quality of the finished job. Even many of us (like me) who’ve been doing jewelry, goldsmithing, and stone setting for a long time still defer, on the especially tricky or important jobs, to those setters known to be particularly good with a certain style of setting work, unless the style in question happens to be our own individual specialty.

by Peter W. Rowe M.F.A., G.G.