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Distinguishing between natural no treatment rubies with heated or new treatment rubies is a very important skill every ruby gemstone buyer should learn before venturing out to buy one.   The price between each levels of treatment can range from the exceptionally expensive US$10,000 per carat for unheated natural rubies to US$1 per carat for new treatment lead-glass filled rubies which has now flooded the market today (this is especially true with Thai and many other dealers on eBay). Understanding what to look for and checking the authenticity of the certificate can make a difference between buying a ruby which you got a great deal for and buying a gemstone that you got scammed as the seller did not inform you what type of treatment the stones is.  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 rubies 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 Ruby

Natural Ruby 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.
  • Boehmite needles
  • 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 rubies with these characteristics.  Please note that it does take some experience to check and verify if the ruby you are looking at is completely natural or not.  However, if you do have a great pair of eyes and can see these inclusions and NONE of the other inclusions described from the guide below, you can be sure that the ruby you have in hand is natural, unheated and untreated, the rarest of all rubies!

Intact and unaltered Calcite Crystals — Photo courtesy from © Paolo Cerruti

Natural Apatite Crystals – Photo courtesy of Photo © Richard W. Hughes

Another intact and unaltered calcite crystal and hexagonal color zoning seen within – Photo courtesy of Photo © Richard W. Hughes

Intact Silk inclusions – Photo courtesy of Photo © Richard W. Hughes

Heated Rubies

Almost all rubies (95%) of rubies today are heat-treated.  There are different types and level of heat treatment in rubies which can be classified from very slight to quite extreme.  Distinguishing these levels of treatment can also affect the price of ruby dramatically.  Heat treatment is used to either develop or intensify a ruby’s natural color.  Heat treatment can also improve the clarity of a ruby 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 heat treat rubies.  Ways of detecting “normal heat” treatment rubies 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 rubies are still not cheap.  Good ones can still cost upward of US$5,000 per carat.   However, before paying these high prices, PLEASE make sure the ruby which you are purchasing has not been subjected to newer or higher step treatments (as shown next topic below) because the price for these rubies can drop dramatically.  A good way to double check if the ruby 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 ruby is only subject to H treatment or H (a) is also acceptable.  If its written H(b) or below then you will know that the ruby has been subject to newer treatments and so you should not pay the price for normal heat ruby.  For all the GRS classification details you can click on the following link: http://www.gemresearch.ch/limiteng.htm

Discoid fractures with tension halos. Notice the disk like fractures with lace like outer healing rims – Photo courtesy from © AGSL

Though this image is not a ruby, the inclusions will look the same in normal heated ruby. This image shows discoid fracture with tension halos and burned, altered mineral inclusions (in the middle) with rounded “cotton” like or “snowball” look — Photo courtesy of © Alberto Scarani

Dotted Rutile Silk and not straight intact lines proves the silk has been burned or the ruby has been heat treated. – Photo courtesy of Photo © Richard W. Hughes

Heated Flux-healed rubies

Extreme heat treatment which induces flux like material in rubies is the next higher step of treating rubies.  On reliable certificate providers as stated above will indicate this rubies as H(b) or below. Treaters add this “foreign” material into the rubies by surrounding the rubies with a flux-like material that becomes molten at extremely high temperatures.  The dissolved flux then fills the fractures and cavities that are open to the stone’s surface which then solidifies into a glass-like substance.  This process improves apparent clarity, but because the clarity of these materials is not completely “natural” the price for these rubies are substantially less.   Again, this will depend on how much residue is presented in the heated rubies, which the labs can classify as minor, moderate or significant residues.   For each level the price will drop accordingly, in average of almost 20% to 50% per carat.  Signs to check for flux healed rubies are explained below.

  • Flux inclusions are generally white and have a glue or sticky look.  But, it might also appear near-colorless, whitish, brownish, or yellow to orange. PLEASE NOTE: Even though these inclusions usually indicate flux induce by the heat treatment process, there are also flux-growth synthetic rubies which are man-made stones and NOT natural rubies.   For more details please read our next post on synthetic rubies which is coming soon.

Flux Residue inclusions. Noticed the glue or sticky look – Photo courtesy of Photo © Richard W. Hughes

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

The newest type of rubies which has flooded the markets in recent years is called lead-glass filled rubies, which 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 brown color that would NOT have been saleable if it was not subject to this type of treatment.   How it works is usually this “bad” looking ruby (if you can call it ruby) are mixed with acid to remove mineralized inclusions making the stone texture soft and weak like a sponge. If you hold the stone at this state it will crumble into powder.  This material then is infused with leaded glass to give back the strength and apparent good looks.  For an average consumer, you would think this is a beautiful natural ruby, which I am getting in a cheap price.  The problem with this type treatment is many as listed below:

  • These stones are not rubies anymore.   It is mixture of natural corundum and lead-glass.  Actually most of these “rubies” have more lead-glass in them, yet they are still being sold as natural rubies in major stores and/or some ebay or online dealers, 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 inform decision in how much you should pay for this type of ruby.
  • Due to not being purely corundum anymore this type of ruby 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 rubies you don’t have to worry about any of the above issues.
  • Also, if you the wearer is not careful in wearing these “hybrid” rubies and for example, accidently 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 in buying rubies it is very important to find out how to check for these types of rubies.  Sure indications are listed below.

  • Gas-bubbles are sure indications of glass-filled rubies 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 rubies

Again, the best way to find out if the stone you are buying is lead-glass filled rubies is by either 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 rubies as “Hybrid”-Ruby  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 Ruby” — a sample certificate can be seen by clicking here: http://www.gemresearch.ch/certs/TreatRub.htm

Gas Bubble inclusion

Gas Bubble seen at the right side of the stone – Photo courtesy from © Wimon Manorotku

Blue and Orange flash effect along structural fractures – Photo courtesy from © Barbra Votaire

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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