Welcome to AGTA GTC's Laboratory Update for November 29, 2005

In this message

  1. The Synthetic Healing of Ruby
  2. Peace of Mind with an AGTA GTC Report
  3. AGTA GTC on the Web

Current turnaround time at the AGTA GTC
5–7 Business Days

The Synthetic Healing of Ruby

One of the least understood treatments applied to any gemstone is that of the flux healing of rubies. Often mislabeled as, and confused with, “glass-filling,” in fact the treatment involves the use of fluxes to “heal” open fractures in ruby. Today, despite the fact that the process has been discussed at dozens of meetings, most jewelers are completely unaware of the treatment method and its impact on a gemstone. The following is designed to shine light into this misunderstood industry corner.

Fingerprint in Thai Ruby

Figure 1. Anatomy of a healed fracture
A well-healed fracture in a ruby lying roughly parallel to the basal plane. The healed areas appear dark, while the undigested fluids are highly reflective and white or brightly colored. Note that the pattern of healing relates to the underlying crystal structure, with angles of healed areas following the underlying crystallographic structure (in this case, at 60/120°). Photo © John I. Koivula/microWorld of Gems

The flux healing process
Flux healing involves heating corundums with borax or other fluxes. These fluxes actually dissolve the surfaces, including the internal surfaces of cracks. The corundum within this molten material then redeposits on the fracture surfaces, filling and healing the fractures shut. Undigested material cools into pockets of flux glass. Essentially this amounts to a microscopic deposition of synthetic corundum to heal the cracks closed. This treatment is applied to virtually all rubies from Burma’s Mong Hsu mines, which have produced the lion’s share of facet-grade ruby over the past 15 years.

Anatomy of a flux-healed fracture

Figure 2. Diagram of a flux-healed fracture
The mechanism of flux healing of a fracture in corundum.

A. Open fracture/fissure, unhealed.
B. During heat treatment, flux enters the fracture and dissolves the walls of the crack.
C. During cooling, dissolved corundum recrystallizes in the crack, thus healing it closed. The newly crystallized ruby is essentially a synthetic ruby grown in the crack alone. It contains small pockets of now-solidified flux glass, along with some trapped gas pockets. For purposes of this diagram, the surrounding natural ruby and the synthetic ruby in the crack are shown in two different colors. In reality, no distinction can be seen between the surrounding ruby and the newly grown synthetic ruby.
D. Any flux glass present on the surface can be dissolved away with acid. The synthetic ruby in the crack is unaffected by the acid, as is the ruby as a whole. (Illustration © R.W. Hughes; modified from Hänni, 2001, SSEF)

Flux healed fracture in Mong Hsu ruby

Figure 3. Flux-healed fracture
Moderate magnification reveals a flux-healed fracture in a Mong Hsu ruby from Burma. The irregular dark areas are pockets of residual flux, while the red areas in between are where the once open fracture has healed shut with microscopic amounts of what is essentially synthetic corundum. Photo © R.W. Hughes

     In the broadest sense, this is akin to the oiling of emerald – both treatments involve reduction of internal reflections from cracks/fissures. Similar to placing an ice cube in water, a filled fracture is much less visible because the filler replaces air (refractive index = 1.00) with a substance that has a refractive index that more closely matches the gemstone itself (1.76–1.77). However, the flux healing of Mong Hsu rubies differs in three important respects:

  • The Mong Hsu ruby treatment is not a fracture filling, but a permanent healing or regrowth of the fractures and fissures, with any residue merely a remnant of the process. In many respects, it is a welding of fractures, similar to the joining of two pieces of metal with heat and a flux to fuse them together.
  • The treatment is permanent and irreversible. Unlike the oil in an oiled emerald, flux remnants will not drain out in the future, nor can they be removed. There is no way to return a gemstone to the untreated state.
  • The treatment actually improves a gemstone’s durability, since the fractures are permanently welded shut.

     In the past, some have argued that the flux remnants are an accidental byproduct of what amounts to "normal" heating. Nothing could be further from the truth. While Mong Hsu rubies are heated for two different reasons (to remove the blue color and heal the fractures), the flux is used solely to heal fractures. This is why fluxes are generally not used when heating clean gemstones (such as pink sapphires from Madagascar) to remove similar blue overtones.

From the above, it should be clear that the flux-healing treatment is entirely different from both ordinary heat treatments, as well as fracture-filling treatments. If lumped together with simple heat treatment, it will completely redraw the map, not just for ruby, but also potentially for the entire gemstone industry. Treatments such as this underscore the need for widespread educational programs, along with modern laboratories, such as the AGTA GTC.

Surface of flux-healed fracture

Figure 4. Surface view of a flux-healed fracture
A highly magnified photo showing a single facet’s surface in reflected light where a fracture breaks the surface in a flux-healed Mong Hsu ruby. The dotted red line shows the path of what was once an open fracture, displaced slightly to the right so you can see surface detail. The irregular black areas are surface cavities where bubbles in the flux were cut through, while the irregular gray areas are residual flux glass that has been polished. Note the lower luster compared with the surrounding corundum. In between the surface cavities and flux glass are healed areas, indistinguishable from the surrounding corundum. Photo © R.W. Hughes

• • • • •

Note: Abstracted from Fluxed Up: The Fracture Healing of Ruby by Richard W. Hughes (with John Emmett). That article was awarded the 2005 Richard T. Liddicoat Journalism Award by the American Gem Society.


Give the Gift of Peace of Mind with an AGTA GTC Report
It is no secret that technological advances have led to an explosion of ever more sophisticated synthetic and treated gemstones. Consumers have a broad range of purchase possibilities and if they lack confidence in our jewelry and gemstone products, they will look elsewhere.
    One of the best ways to inspire consumer confidence at the point-of-sale is to present gemstones with an AGTA Gemological Testing Center Identification or Origin Report. These attractive reports can be the difference between the choice of a fine gemstone gift, or some other product.
We would remind our customers that with the holiday gift-giving season rapidly approaching, the demand for our gemstone-testing services will also increase. Beat the rush and submit your gemstones now. This will ensure that you have professional reports at the ready when it comes time to close a sale.

Ruby ID Report

The AGTA Gemological Testing Center Identification Report provides a perfect point-of-sale tool for consumer peace of mind.

AGTA GTC on the Web
A number of clients have asked us to consider making our gemological bulletins available to a wider audience. Towards that aim, over the past few months we have built a website specifically for the AGTA Gemological Testing Center. It is now live and offers a complete archive of our e-mail bulletins, along with a full description of the lab and its services.
     See it at www.agta-gtc.org or link from AGTA’s regular site, www.agta.org.

Web Screen

The new AGTA GTC website offers the most up-to-the-minute gemological news, along with a full description of the lab and its services.

The AGTA Gemological Testing Center provides the industry and the public with a complete range of lab services, including gemstone identification, origin determination and pearl identification. Located in New York City, the laboratory is equipped with the latest, technologically advanced, investigative equipment. The AGTA GTC is committed to providing excellent service, superior value and outstanding quality. A complete list of services and detailed pricing information is available on our website, www.agta-gtc.org. Please contact us with any questions.

American Gem Trade Assocation Gemological Testing Center
18 East 48th St., Suite 502
New York, NY 10017, USA
Tel: 212-752-1717; Fax: 212-750-0930
E-Mail: info@agta-gtc.org; Web: www.agta-gtc.org
© 1999–2005 American Gem Trade Assocation Gemological Testing Center. All rights reserved. Users may download this information for their own private, non-commercial use. Any other reproduction of this document (text or graphics) without the express written consent of the AGTA GTC is strictly prohibited.
Problems? Praise? Contact the Webmaster.


The AGTA GTC publishes free bulletins with the latest gem news. Sign up here.


Site Search

search tips     sitemap