Blue Sapphire Buying & Treatment Guide – How to buy and tell the difference between natural unheated, heated, lattice diffusion treatment, and the brand new “glass-filled” sapphire?

Distinguishing between natural, no treatment sapphire with heated or new treatment sapphires is a very important skill every gemstone buyer should learn before venturing out to buy one.   The price between each levels of treatment can range from the exceptionally expensive US$5,000 per carat for unheated natural sapphires to US$1 per carat for the new treatment lattice-diffused sapphires which has now flooded the market today (this is especially true with many dealers on eBay especially in Thailand). Understanding what to look for and checking the authenticity of the certificate can make a difference between buying a sapphire which you got a great deal for and buying one that you got scammed for as the seller did not inform you what type of treatment the stone has had.  I hope this guide will provide you the basic understanding in how to distinguish the different type of treatments.  I do want to emphasize that even though you have read this guide completely and understood the basics, it does take years of experience of seeing sapphires to truly understand and distinguish the different treatments.  If there is any doubt in your purchase — even that slight 1% chance — it is always best to double check the stone from a reliable gemstone laboratory or trustworthy gem dealer.

Unheated, Untreated, Completely Natural Sapphire

Natural Sapphire that are NOT heated or treated are quite easy to distinguish if they have natural inclusions inside, which you can see through a microscope and normal 10 times (10x) magnification loupe.  Natural inclusions include the following:

  • Intact, fine, needle-like Silk (rutile needles) intersecting at 60 degrees angle in the same plane or other fine needles at near right angles.
  • Fingerprint inclusions
  • Angular, straight or hexagonal growth zoning or banding
  • Straight, angular and possible color zoning and color banding
  • Unaltered mineral inclusions, clear or opaque color, that might show angular faces
  • Intact two-phase inclusions

Below are some sample images of sapphires with these characteristics.  Please note that it does take some experience to check and verify if the sapphire you are looking at is completely natural or not.  However, if you do see these inclusions and NONE of the other inclusions described from the guide below, you can be sure that the sapphire you have in hand is natural, unheated and untreated, the rarest of all sapphires!

Intact Negative Crystal
Intact Negative Crystal in Madagascar Blue Sapphire. Photo courtesy from © GGTL Laboratories
Intact Rutile Silk Inclusions
Intact Rutile Silk Inclusions which proves this is natural blue sapphire.  Photo courtesy from © GIA

Heated Sapphires

Almost all sapphires (95% of them) today are heat-treated.  There are different types and level of heat treatment in sapphires which can be classified from very slight to quite extreme.  Distinguishing these levels of treatment can also affect the price of a sapphire dramatically.  Heat treatment is used to either develop or intensify a sapphire’s natural color.  Heat treatment can also improve the clarity of a sapphire by removing or reducing inclusions by making them less visible.  The way this works is quite technical and I will not be explaining it in this guide, but you get an idea why people love to heat sapphires.  Ways of detecting “normal heat” treatment sapphires is by seeing the following inclusions:

  • Discoid fractures with tension halos (looks like disk-like fractures with lace-like outer healing rims, which are caused by expansion of natural crystal inclusions)
  • Burned or altered mineral inclusions with rounded, often whitish, “cotton” like or snowball” appearances
  • Broken silk or partially “reabsorbed” rutile needles
  • Ruptured two-phase inclusions and negative crystals
  • Sintered surface areas, especially around the girdle

Prices for normal or slightly heated sapphires are still not cheap.  Good ones can still cost upward of US$3,000 per carat.   However, before paying these high prices, PLEASE make sure the sapphire which you are purchasing has not been subjected to newer or higher step treatments (as shown next topic below) because the price for these sapphires can drop dramatically.  A good way to double check if the sapphire is what is stated is by asking your jeweler or gemstone wholesaler for a reliable certificate with the stone.  On a GRS certificate (GemResearch Swisslab – one of the reliable color gemstones certificate laboratories in the market) it will state the sapphire is only subject to H treatment or H (a) is also acceptable.  If it is written H (Be) or the newer hybrid sapphire treatments then you will know that the sapphire has been subject to newer treatments and so you should not pay the price for normal heat sapphire.  For all the GRS classification details you can click on the following link: http://www.gemresearch.ch/limiteng.htm

This image shows discoid fracture with tension halos and burned, altered mineral inclusions (in the middle) with rounded "cotton" like or "snowball" look.. This proves this blue sapphire is heated.
This image shows discoid fracture with tension halos and burned, altered mineral inclusions (in the middle) with rounded “cotton” like or “snowball” look. This proves this blue sapphire is heated. Photo courtesy from © GGTL Laboratories
Partially healed fissure containing melted residues which proves this blue sapphire has been heated.
Partially healed fissure that contains melted residues.  Again, this blue sapphire has been heated. Photo courtesy from © GGTL Laboratories

Lattice Diffusion Treated Corundum

Extreme heat treatment which induces foreign materials in sapphires is the next higher step of treating sapphires and is called Lattice diffusion.  On reliable certificate providers as stated above they will indicate these new treatment sapphires as H(Be). Treaters add this “foreign” material into the sapphires by heating it in extreme temperatures and diffusing substances like beryllium (light element) or titanium (heavy elements) into it.  These elements helps enhances the blue sapphire color and therefore makes the stone look more vivid or blue compared to the original state.  As these elements were introduce by man, this makes diffused-treated sapphires less rare and therefore worth substantially less.   Signs to check for diffused-treated sapphires are explained below.

  • Lattice diffusion with heavy elements:
    • Color concentrations along facet junctions and girdle edge
    • Localized or blotchy color that “bleeds” inot pits and surface-reaching fractures
    • Above features are best seen trough gem’s pavilion (gem faced upside down or bottom face towards you) immersed in water and diffused light under it.  This allows you to see the fact junctions without distraction of sparkle of the gemstone
  • Lattice diffusion with beryllium
    • This light element is diffused in the sapphire to remove or lighten the blue color in overly dark sapphires.  While initially doing the treatment there might be some traces of yellow color in the stone’s interior.  This “yellow color” however can be removed with subsequent heat treatment, which will make the sapphire “retain” its blue color and therefore make it more marketable.
    • Magnification and water immersion (as indicated lattice diffusion with heavy elements) might reveal a colorless zone around the outside of an otherwise blue stone.

Images in how to detect both types of diffusions are provided below.  Price for these types of sapphires are substantially cheaper (from US$1 to US$20 per carat) because new elements have been introduced by man to make these “less rare and not so good looking sapphires” more marketable.

This blue sapphire shows "shallow" depth of foreign element treatment as you can see from color concentrations along facet junctions and girdle edge. This proves this blue sapphire has been treated with lattice diffusion with heavy elements. Photo courtesy from © Robert E. Kane et al., “The Identification of Blue Diffusion-Treated Sapphires,” Summer 1990 Gems & Gemology; photos by Shane F. McClure.
This blue synthetic sapphire shows “shallow” depth of foreign element treatment as you can see from color concentrations along facet junctions and girdle edge. This proves this blue sapphire has been treated with lattice diffusion with heavy elements. Photo courtesy from © Robert E. Kane et al., “The Identification of Blue Diffusion-Treated Sapphires,” Summer 1990 Gems & Gemology; photos by Shane F. McClure.
This pictures show the colorless zone around the outside of an otherwise blue stone, which proves lattice diffusion with beryllium. Photo courtesy from © Richard W. Hughes
This pictures show the colorless zone around the outside of an otherwise blue stone, which proves lattice diffusion with beryllium. Photo courtesy from © Richard W. Hughes

Lead-Glass Filled Sapphires (New Treatment or Phua Mai in Thai)

The newest type of sapphires which I just heard of a few months back is lead-glass filled sapphires, which was a surprise because I thought it existed only in the case of rubies. If you do find a sapphire which is written as “composite sapphire” then you will know this is lead-glass filled and the average price is US$ 1 per carat or less.  These stones are not worth anything because in their natural state, the rough would have been an ugly, highly included gray color that would NOT have been saleable if it was not subject to this type of treatment.   As this is a new type of treatment I am still not sure how they have treated these stones, but I will assume it will be very similar to its corundum cousin (ruby).  Please be careful with these type of stones as you might think this is a beautiful natural sapphire, which I am getting in a cheap price.  The problem with this type treatment is many as listed below:

  • These stones are not sapphires anymore.   It is mixture of natural corundum and lead-glass.  Actually most of these “sapphires” have more lead-glass in them, yet they are still being sold as natural sapphires, which makes this a major disclosure issue.  If the sellers actually disclose the treatments of these stones to their clients, the purchaser can then make an informed decision in how much one should pay for this type of sapphire.
  • Due to not being purely corundum anymore this type of sapphire if you set in jewelry without informing the setter will get ruined in a second.  If you torch the ring for resizing and it touches the stone for a second it will crack.  If you re-plate your Rhodium plate white gold ring it will destroy the stone.  For natural sapphires you don’t have to worry about any of the above issues.
  • Also, if you, the wearer is not careful in wearing these “hybrid” sapphires and for example, accidentally spill some lemon juice while eating fish the stone will slowly decay in few days and your supposedly “beautiful” stone will now look like it was thrown from 50 storey high rise building.

Therefore, if you are in the market to buy sapphires it is very important to find out how to check for these types of sapphires.  Sure indications are listed below.

  • Gas-bubbles are sure indications of glass-filled sapphires or synthetics.  Usually very easy to spot under microscope or a loupe with dark light background.
  • Blue and Orange flash effect along structural fractures when put under a black light is also a key indication of lead-glass filled sapphires

Again, the best way to find out if the stone you are buying is lead-glass filled sapphire is either by having a great pair of eyes and check for the signs above or getting the stone certified by a reliable lab.   GRS certificates will classify these sapphires as “Hybrid”- Corundum and will have the following comment “Heat-treated and filled with a foreign solid substance (including lead).  Special care when handling.  Also known has Composite Sapphire”

Glass-filled blue sapphire lot that came across our office last month. Looks like normal sapphires with naked eye, but when you see it under gem loupe or microscope you can tell its not a "natural" blue sapphire. Photo courtesy from © Thai Native Gems
Glass-filled blue sapphire lot that came across our office last month. Looks like normal sapphires with naked eye, but when you see it under gem loupe or microscope you can tell its not a “natural” blue sapphire. Photo courtesy from © Thai Native Gems

I hope the above guide is helpful and if you have any additional questions please feel free to provide your comments below or send me a message at sales@thainativegems.com.

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12 thoughts on “Blue Sapphire Buying & Treatment Guide – How to buy and tell the difference between natural unheated, heated, lattice diffusion treatment, and the brand new “glass-filled” sapphire?

  1. Thank you very much give to this information very usefull is buying gemstones, and peoples are in gem business field or not, are borth them have get from knowlege &experiance about this article.i am very appriciated with you this article. thankyou.

      1. This type of stones are in the market . Used in most silver jewellery. It doesnt matter as long as sold cheep and tell the customer its way of treated. Because of the good natural treated gudas saphires are expensive in price .

      2. Thanks Riza for your comments. Agree with you that all jewelers and manufacturers should disclose the treatments and if they don’t I hope these buying guides help. This is the reason why I created this blog as I believe being more transparent will help the gemstone trade overall.

  2. hi i think this blog is having very good message about gemstones. you know what birth stones depend on according to their birth date. A colourful assortment of dazzling gemstones generally bears month wise association. Both traditional as well as modern category involves similar correlations.

  3. My husband just recently bought me a blue sapphire glass for a wedding anniversary. I am just curious to know what is the best way to take care of it so that it will stay around for awhile. It’s good to know that regular treatments help concentrate the colors.

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