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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

Colored Gemstone
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.

  1. Analyze the proportion of the gem you're working with; use dividers to mark the depth of the seat on each prong.
  2. 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).
  3. Remove the metal flashing created by the bur next to the prongs ("Remove the Flashing," December 1999, p. 97).
  4. 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).
  5. 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).

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.

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.

Relief-Cutting a Bearing with a Bud Bur

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.

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.

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.

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.

 

 

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.

Tips for Bending Prongs

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.

 

 
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.

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.

 

 

Prong Pusher

You also can use a prong pusher to move prongs. In all situations, move the prongs in very small amounts.

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

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.

 
   
Potential Problems to Watch For

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.

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.

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.

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.


Copyright © 1999 by Bond Communications.



 

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