What A Drag

Gemstones & Pearls:Gemology

What A Drag

Examination could show whether a gem was fractured before or after polishing

The silver lining in the notorious Fred Ward emerald case is that several gemological tests, such as examination of a gem's Newton rings, have been developed and perfected since the case started (Professional Jeweler,November 1998, p. 31). The tests require further study, but the findings may soon help jewelers, dealers and insurers determine whether fractures were present before cutting or if they resulted from trauma to a faceted stone.

Another test involves checking for drag lines. When a gemstone is cut and polished in a direction perpendicular to the length of the fracture, "undercutting" occurs. Undercutting is the breakage of tiny pieces of host material along the fracture, where the crystal integrity is weakest. With the action of the cutting wheel, these particles carve minute drag lines on the opposite side of the fracture. Separately, some particles form tiny wedges or divots, embedded in the fracture itself. Conversely, no such drag lines would occur in an already faceted gem unless it is cut again (with a resulting weight loss).

Drag lines appear on only one side of a cavity or fracture, as shown in this illustration of a Colombian emerald (not the one in the Ward case). Polishing lines occur on both sides. This illustration of the emerald in the Ward case shows polishing lines on both sides of the fracture. But the Gem Quality Institute found no drag lines in this view, indicating the fracture occurred after polishing.

Ward's Emerald
The Gem Quality Institute, Los Angeles, CA, examined the large fracture visible across the table of the 3.66-ct. emerald in the Ward case in September 1998 (after the trial had ended) and issued a report stating: "On this stone no drag lines or divot areas were found emanating from the major fracture on the table facet ... while it is impossible to precisely date any fracture, it appears likely that the major fracture on the table was not present at the time of last polishing."

Results of GQI's examination strongly suggest the fracture occurred after the gem was polished, supporting Ward's claim the emerald was fractured when the plaintiff whacked the ring against a kitchen counter.

Interestingly, the Gemological Institute of America's Gem Trade Laboratory came to the opposite conclusion after examining the same emerald four years earlier. GIA's report states: "It is the finding of this Laboratory that the flaw in question is inherent to the stone and was present when the stone was last polished. This is evidenced by the presence of interrupted polishing lines, polishing drag lines and undercutting where portions of the fracture reach the surface."

Second Opinions
Anyone buying a stone with fractures or fissures should examine it for visible drag lines. For further certainty or if a dispute arises concerning whether a fracture was present before or after cutting, take great care in obtaining a consensus of opinion on drag lines from accredited testing facilities.

– by Robert Weldon, G.G.



Copyright © 1999 by Bond Communications.


 

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