While the NRC carries untreated and heat-treated rubies only, the following treatments and enhancements are very common. People have been treating gemstones to improve appearance for a very long time. It spans from dying low-quality pieces of lapis lazuli, to heat-treating rubies with a small fire and a pipe, to foil-backing stones, and more spanning back to antiquity. Point being, treating gemstones is not new for the gem industry.
It should be noted that some individuals sell treated gemstone material as natural, untreated material. This is why reputable dealers disclose any and all gemstone treatments to the customer before purchase, so they can make an informed decision.
While there is always research and developments being made, there are three main types of treatments used for rubies.
Photos by Ted Themelis – Heat-treated Mong-Hsu ruby
Heat treatment is done to improve both clarity and color of rubies. Sri Lanka rubies become a more intense red, Thailand ones lose their brownish color, and Möng Hsu rubies (not to be confused with Mogok rubies) from Myanmar lose their dark, unattractive cores. Moreover, this is a stable and permanent treatment; meaning the effects will not fade due to regular wear and occasional cleaning.
Silk (rutile needles) does not recrystallize until somewhere around 1,200 to 1,600 degrees celsius, and their appearance does change at the microscopic level. Silk can show rainbow colors that fade with heat-treatment, and even dissolve at higher temperatures like other inclusions. It often leaves behind some types of traces due to the high-melting point. Traces of silk are usually easy to spot due to their specific orientation.
Photos by Ted Themelis
If a ruby has been heat-treated, it is also possible for it to have been heated in the presence of flux to help heal severe fractures. Various inclusions also rupture at different temperatures, making the interior of some heated rubies white and fuzzy. The ruby above has not been cut since being heated, also showing a fuzzy, recrystallized surface too.
Cavities and fractures can cause a huge loss of clarity in rubies and other gemstones, which is why fracture-filling treatments exist. The first is fracture-filling with colored, lead glass. This can improve not only the visible clarity but the color in certain instances. Note that the treatment has a caveat of not being durable, and can be damaged with cleaning in sonic jewelry cleaners. It is one of many reasons that disclosure is so important in the gem industry.
Blue and orange flashing effect in glass-filled rubies. It is a hallmark of the treatment, along with the high visibility of the glass flow lines in this case. Field of View: 3.11mm
In the event of cavities that weaken a ruby’s durability, they are heated with a type of material called flux. This material fills the cavities and allows the ruby to heal the fractures itself. The result is much more durable than glass-filling, though it is not unusual to have residual flux.
Of the three most common treatments, diffusion is the least popular and the most controversial. Sellers usually resort to this method when heat-treatment is ineffective. The rubies are heated and have beryllium added in at high temperatures. In essence, a white sapphire can be made into a ruby, depending on how and if the corundum will take the treatment.
It brings into question whether or not the stone should actually qualify as a natural ruby, or treated white corundum. Note that the extra color does not penetrate the whole stone, only going through a portion of the surface. If the corundum is cut open, the center will still be white (or whatever the original color was).
Notice how the blue for the sapphire does not penetrate the stone as deeply as the orange. This is because the elements diffused into the blue sapphire, iron and titanium, are heavier and larger elements than the beryllium diffused into the orange sapphire. Iron is 26 on the periodic table, Titanium is 22, and Beryllium is 4. This is why the orange, beryllium diffused sapphire shows better color penetration than the blue sapphire. It is also why chromium (24 on the periodic table) is not popular for diffusion.
While controversial, this treatment is stable and permanent, though major chipping could cause loss of the colored layer. It also provides consumers an additional selection of rubies at a viable price-point. Like all other treatments, it must be disclosed to the customer before purchase.
With the diffusion treatment, it is also possible for a feature called synthetic overgrowth to occur. The corundum is heated to high, near-melting temperatures to allow the added chemicals to penetrate the stone. As the stone cools, the outer surface recrystallizes. Synthetic overgrowth is what the re-crystallized surface of the stone is called, since the base material did form naturally.
While not always possible, little blue dots may be found in the diffused corundum material. They are present in the orange diffused sapphire above too. This is diagnostic of beryllium-diffused rubies. Because the heating for diffusion is so intense, traces of titanium will “bleed” blue.