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
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 ifyou 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.
Peter W. Rowe M.F.A., G.G.
Commercial and custom jeweler and metalsmith
Graduate Gemologist and Lapidary
Opinions expressed here are solely my own....... and subject to change
according to my mood and the state of my art ....
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