Lore of the Rings

November 1998

Gemstones & Pearls:News

Lore of the Rings

The curious multicolored rings sometimes seen when a gem is brought in contact with an optically flat surface may provide the key to detecting the age of fractures, say two gem experts

Necessity has given birth to an invention that may help detect whether a fracture in a gemstone is old or new. Placing an optical flat on a flat facet of a well-polished gemstone allows you to see "Newton rings," which are concentric rings appearing between the flat and the gem's surface. (An optical flat is a piece of fused silica or quartz flattened and polished to extremely high tolerance.)

Optical flats have not been used in gemology until now. The idea is the brainchild of Ray Zajicek, owner of Equatorian Imports, Dallas, TX, and Fred Ward of Gem Book Publishers and Blue Planet Gems, Bethesda, MD. The two men hit upon the technique while trying to find a way to solve Ward's thorny legal troubles with a 3.66-ct. emerald (Professional Jeweler,April 1998, p. 49).

Newton Rings
The phenomenon of Newton rings may determine whether gemstones were damaged before polishing, which then would indicate whether it occurred before or after it was sold it to a customer. If you place an optical flat over a facet that contains a fracture, Ward says, one of two things may happen:

  1. The spherical nature of the concentric Newton rings is broken at the fracture point, indicating a dislocation in the surface of the gem. This would suggest the gem was damaged after faceting, otherwise the faceting process would have smoothed the surface.
  2. The spherical nature of the concentric rings stays intact, suggesting the fracture occurred before it was faceted. This means that if the history of a gemstone is documented well, especially its weight after cutting and polishing, you could determine whether a fracture occurred at the gem's point of origin (naturally) or after faceting.

New Tool
If proven effective, this gemological tool could be used by jewelers who take in gems and jewelry for repair, gemstone dealers who buy overseas and insurance companies investigating claims.

Zajicek first noticed Newton rings on gems placed flat under a glass at his display counter. Ward saw rings on gems in circular gem containers with tight-fitting plastic lids. Both wondered whether there could be a gemological application.

The two conducted months of experiments, documenting and photographing dozens of gemstones to understand the nature of fractures – induced, natural and in repolished gemstones. Ward says he also hired fracture experts to review his findings.

New Evidence
The experiments with the optical flats were undertaken as a way to help bring an end to Ward's continuing legal struggle. He's trying to prove a large fracture occurred in an emerald after he sold it and not before, as the plaintiff alleged in a lawsuit she filed against him.

Ward says he did disclose two small fissures in the pavilion of the emerald at the time of sale, but contends the large fracture occurred later when the plaintiff knocked her ring at a kitchen counter. She says the fracture was always there and was fracture-filled and not visible before it was sold. A judge agreed with the plaintiff and ruled in her favor.

Based on the Newton ring evidence and other findings, however, Ward filed a motion for a new trial in mid-August. A decision on a new trial was pending at press time. With the studies Ward and Zajicek have conducted with optical flats, they hope to prove the fracture occurred when the ring was knocked – and that it was fracture-filled some time after that. Ward's photographs illustrate the use of the optical flat in fracture detection.

This picture of a 3.66-ct. emerald shows a large fracture system across the table. The emerald is at the center of litigation about whether the fracture occurred naturally and was filled before it was sold or whether it occurred when the new owner hit the stone on a counter and the fracture was filled later.
  The same emerald, under an optical flat, shows interrupted "Newton rings," or rings that are not uniformly concentric in the area of the fracture. This indicates a surface crack happened after the emerald was faceted and sold, otherwise the surface would have been smoothed during the faceting process.

All photographs © Fred Ward, 1998
A natural fissure on the pavilion of the same emerald was disclosed to the consumer at the time of the sale. This picture, taken with an optical flat over that fissure, shows uninterrupted concentric "Newton rings." This suggests the fissure, which was present at the time of faceting, suffered no changes, even though the emerald endured later trauma.

 What Is a Newton Ring?

Newton rings are the concentric circles that appear when two flat transparent or semitransparent surfaces are in close proximity.

Named for scientist Sir Isaac Newton (of law of gravity fame), Newton rings are caused by light reflection and refraction. The rings can be seen on the flat polished facets of gemstones when glass, an optical flat or even a transparent gemstone case lid is held close. Seen here is an optical flat in contact with a gemstone.

Newton rings also commonly appear when using a transparency on an overhead projector, when printers and photographers scan film and on soap bubbles.

– by Robert Weldon, G.G.



Copyright © 1998 by Bond Communications.


 

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