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January 2000
For Your Staff: Selling Quality
Ship Shape, Part 2
– by Tom Weishaar, JA® Certified Master Bench
Jeweler,™ Shop Manager, Underwood Jewelers, Fayetteville,
AR
Knowing how to professionally set marquise and pear-shaped
colored gemstones in prongs demonstrates another aspect of quality
in your shop
Diamond
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Colored Gemstone
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| Color isn't the only difference between diamonds
and other marquise and pear-shaped gems. Colored gemstones are
often cut to proportions different from those of diamonds. The
differences affect the way you set these gems. |
Last month's installment of The JA Professional's Guide to
Fine Jewelry Craftsmanship (December 1999, p. 99) dealt with
stones cut to "diamond proportions" and the quality
stone-setting features associated with them. This installment
explains how to set stones cut to other proportions.
When setting a gemstone, it's critical to consider its inherent
characteristics and the style and proportions in which it is
cut.
What's the Difference?
Most bench jewelers working in a retail environment are highly
capable setters of diamonds, the most common stone they work
with and the most forgiving. Many of these bench jewelers routinely
"snap" diamonds into prongs, twist them with tweezers
and hammer metal over them.
We don't recommend these setting practices, but recognize
diamonds usually can withstand this type of abuse unscathed.
The problem is that the forgiving nature of diamonds reinforces
bad stone-setting habits.
These bad habits often lead to trouble when used to set colored
gemstones. The three leading factors contributing to damage of
colored stones during the setting process are:
- Improper seat cutting and point prong preparation.
- Improper prong bending.
- Improper finishing.
Tips for Setting Marquise & Pear-Shaped Colored Gems
Murphy's law of stone breakage: Any damage to gems while being
set will be followed five minutes later by a call from the owner
checking on the status of the jewelry.
Here are some procedures to help minimize or eliminate damage
while setting:
- Wash your hands before handling colored gems. Polishing compounds
and metal fragments imbedded in your fingertips can damage many
of the softer gems.
- Clean your bench pan and place a soft towel in it. Many bench
jewelers accidentally bump gems off their bench into a bench
pan loaded with tools and files. The result: damage to the customer's
gem!
- Place a clean soft cloth to the side of your bench on which
to place the gem when it's not being measured or fitted.
Critical Setting Steps
Here are the steps to follow in setting gems cut to other
than diamond proportions.
- Analyze the proportion of the gem you're working with; use
dividers to mark the depth of the seat on each prong.
- Using a straight-walled setting bur, cut a seat for the gem.
Remove up to one-third of the prong's original thickness (see
"Bur a Seat" illustration, December 1999, p. 97).
- Remove the metal flashing created by the bur next to the
prongs ("Remove the Flashing," December 1999, p. 97).
- Use a small ball bur or heart bur to create a channel or
seat into which you can set the point of the gem ("Create
a Seat," December 1999, p. 98).
- Use a small bud bur, ball bur or drill bit to open up the
junction of the "V" prong so no part of the gem's point
touches the prong ("Open the V," December 1999, p.
98).
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Prongs Cut With a Setting Bur
Colored gems often are cut for maximum weight retention or
to enhance color, so they may have bulbous pavilions, thin crowns
and/or wavy girdles. Setting burs are not designed to cut a seat
that matches the pavilion angles of most colored gems.
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Pressure Points
Setting colored gems into heads with seats created using only
a setting bur can cause pressure points. If not removed before
bending the prong, these can damage a fragile gem during the
setting process or normal wear. To avoid pressure points, relief-cut
the prongs using a small bud bur or ball bur. By cutting the
bearing angles to match the profile of the gem, you disperse
pressure over a wider area.
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Relief-Cutting a Bearing with a Bud Bur |
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Well-Seated Gem
The prong's bearing angles precisely match the profile of
the gem's pavilion. Also, the pavilion is elevated slightly above
the upper gallery wire of the head. When the gem's pavilion makes
contact with the upper gallery wire, the wire's image can reflect
back through the gem, reducing its overall beauty. Contact at
this location also creates a pressure point that could damage
the gem if bumped during normal wear.
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6. Complete the prefinishing, making sure:
- The gem will be level when set.
- All tool marks are removed.
- Final shaping of the point prong is done and the head is
prepolished.
7. Set the gem by:
Placing it in its seat and partially bending the back two
prongs over the gem incrementally and one at a time.
- Ensuring the gem is level through the process.
- Fully bending the back two prongs.
- Final shaping and matching the prongs.
A Key: Stay in Control
When setting a fragile gem, it's essential you remain in complete
control of the setting process. Uncontrolled bending may lead
to a rounded, hooked prong and can chip the gem because excessive
pressure is placed at the wrong location. Here are some ways
to control bending.
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Notching a Prong
Notching ensures the prong bends where it should to set the
gem properly. Notch the prong with an 8/0 saw blade just above
the girdle line. Notching the prong is especially helpful when
the gem has thick or thick-to-thin girdles.
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Back-Cutting a Prong
Do this when a prong is particularly thick or it's impossible
to cut a notch on the inside of the prong.
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Splitting a Prong
This cuts in half the amount of pressure required to bend
prongs onto the gem while effectively maintaining the holding
power of two prongs when their mass is combined.
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| Tips for Bending Prongs |
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Parrot Beak Across the Head
Avoid this position when bending prongs because it leads to
damage and the potential misalignment of the gem through the
setting process.
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Flat-Nose Pliers on Top of Prongs
Use modified flat-nose pliers and bend from the top when the
prongs are in the vertical position. Bending prongs is easier
when they are longer than required. Be careful: the excess length
gives you better leverage but also increases the pressure point.
When using this method, you can file one side of the pliers thin
to avoid contact between the gem and the tool. |
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Parrot Beak Pliers Brace Prong Bottom
Once the prongs are past upright vertical alignment, you can
use parrot-beak pliers to gently pull them down onto the gem.
This method doesn't put undue pressure on the gem.
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Prong Pusher
You also can use a prong pusher to move prongs. In all situations,
move the prongs in very small amounts.
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The JA® Professional's Guide
to Fine Jewelry Craftsmanship Marquise and Pear-Shape Colored
Gem Setting
By Mark B. Mann
JA Director of Professional Certification
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Professionally Executed Setting of Marquise and Pear-Shaped
Colored Gems
- A. The gem is level, tight and secure.
- B. Prong angles range around 75.° The angles depend largely
on the gem's proportions.
- C. Prong contact ranges between 30% and 50% and is consistent
from prong to prong. You have some flexibility when using colored
gems with little crown height.
- D. Prong height ranges between 60% and 80% and is consistent
from prong to prong. Again, this is somewhat flexible when using
colored gems with little crown height.
- E. The removal of metal from the prong for the bearing is
not less than 40% nor more than 50%.
- F. The flashing of metal has been removed from the prong
where the bearing was prepared.
- G. The gem and point prong are in contact, but the extreme
point of the gem doesn't touch the point prong (unable to see
after the gem is set).
- H. There are no chips, abrasions or damage to the gem as
a result of the setting process.
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| Potential Problems to Watch
For |
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Prongs with Visible Space Between the Bearing and Gem
There should be no visible or open space between the stone
and the seat prepared for it at and near the girdle.
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Prong Angle Too Steep to Accommodate
the Gem's Heavy Pavilion
The prong angle needs to accommodate the stone's proportions.
These prongs are too steeply angled for the heavy pavilion.
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Poor Contact at Point Prong
When using a V-prong, you must modify the V to fit the point
of the imprecisely cut colored gem.
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All Prong Seats Are Cut to Conform to the Varied Proportions
of the Imprecisely Cut Colored Gem
All prong tips should "fit" the stone and provide
a secure bearing in which it can be seated.
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Copyright © 1999 by Bond Communications.
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