How to distinguish between natural ruby, sapphires and emeralds from synthetics and imitations

To start today’s blog post I want to first tell you a true story about what happened to my friend who bought a ruby from Myanmar (Burma) when he visited there.  This same story can occur anywhere in the world but especially in countries where consumer protection is less stringent.

Tomchai was visiting Myanmar (Burma) with a tour group and was enjoying his time as he didn’t have to stress in planning anything during the trip.  Near the end of the tour his tour guide took them to a ‘large’ retail jewelry shop where he saw some amazing gemstones and jewelry.

One thing which really stood out for him was a 5 carat ruby which looked amazing and the price was substantially cheaper than similar ones you can get in Bangkok, Thailand.   Also knowing that Myanmar is famous for premium gemstones especially rubies, Tomchai thought why not get one ‘from the source.’

After asking a few questions, and seeing that he is inside a large store, he was confident that the retailer he was dealing with was trustworthy as everything else in his trip worked out perfectly.

Tomchai decided to buy the ruby and received an in-house certificate from the shop which made him even more confident that he made the right purchase.  He brought the ruby back to Bangkok to give it to me so I can set the stone in his new custom ring.

While giving it to me, he told me to check it and let him know my thoughts regarding the ruby.  Using my office microscope I checked the stone and almost immediately I saw ‘curved striae,’ which is the fastest way to identify a ‘flame fusion’ synthetic ruby.

I unfortunately had to convey to him the bad news which made him pretty angry as he paid his hard earned money on this synthetic ruby and the seller had not disclose it.

Separating natural gems from synthetics (or imitations) is definitely one of the most important skills, we as gemologist have to learn as it is essential when buying or selling any gem.   Without this basic knowledge one can lose money and damage their reputations very quickly.   

Also, once one has gained the knowledge in distinguishing these synthetics or treatments it is equally important to disclose it to people you deal with or else reputation and financial consequences can be severe.  So, there is no excuse of lack of disclosure or lack of knowledge.

In this blog post, I will try to summarize what we as gemologist check to see the difference between natural, synthetics or imitations.

First the definitions of synthetics and imitations are provided below:

Synthetics gems are made in a laboratory (or manmade) and essentially have the same chemical composition, crystal structure, and properties as natural gemstones.

Imitations gems (also called simulants) can be both natural and manmade.  They only look like the gems they are replacing, while their chemical compositions and properties are completely different from the natural gems they try to imitate.

Ruby classification:  (A) Flame-Fusion Cabochon Ruby – Synthetic  (B) Unheated & Untreated Natural Mozambique Ruby (C) Heated Natural Burmese Ruby  (D) Glass-Composite (or Glass-filled) Ruby.   Myth – the cleaner the stone the higher chance it is a synthetic. However, as seen in the image above this is not true and in fact the only way to tell if ruby is natural or synthetic is by checking for inclusions under microscope. © Thai Native Gems

Synthetic Gems

Clarity characteristics are often the best way to check synthetic gems and the method in which they were manufactured.  Below I will provide the most typical manufacturing methods and some photos that show the most common inclusions that typically found in synthetic gems.

Flame Fusion Synthetic

Visual Characteristics

  • Curved color banding or parallel curved lines called curved striae
    • In contrast, natural gemstones have straight or angular growth patterns
  • Gas Bubbles might also be presented

How to detect

  • Synthetic Rubies – Easy to detect curved striae in ‘red-color’ synthetic ruby through dark field illumination setting
    • Dark field illumination is the normal setting in gem microscope or portable dark field loupe.
  • Synthetic ‘Blue’ Sapphires – Curved color banding ‘blue’ sapphires is a little more difficult to detect through normal dark field illumination, but using ‘diffused’ light can help.
    • One can create diffused lighting by placing a translucent filter between the stone and light well. Translucent material includes white plastic, sheet of paper or plain tissue
  • Synthetic ‘Yellow or Orange’ Sapphires – Difficult to see through microscope as blub produces a strong light which overwhelms faint yellow or orange banding. A blue filter works best in this situation
    • Blue filter includes clear blue transparent sheet or blue plastic

One of most common synthetics found in corundum (ruby or sapphire family) or spinel is made through flame fusion melting process.

In flame fusion, powder chemicals are dropped through a high-temperature flame.  As they melt, they fall onto a rotating pedestal, where they crystallize and form an elongated cylindrical synthetic crystal called a boule.   This boule is eventually cut to make several individual synthetic gems.

Due to this manufacturing process, it is easy to distinguish synthetic gems compared to natural as they have curved color banding or parallel curved lines, called curved striae while natural gemstones have straight or angular growth patterns.

Flux Growth or Hydrothermal Synthetic

Flux Growth Visual Characteristics

  • Coarse looking fingerprint-like inclusions
    • Coarse looking means white and high relief
    • Natural gemstones have liquid droplet fingerprint inclusions which is ‘less’ coarse like than flux growth synthetics
  • Wispy Veils
  • Tiny droplets pattern called “rain”
  • Parallel, uniform growth planes – sometimes called the “Venetian blind effect”
  • Platinum crystals, often in the form of triangular or hexagonal platelets
    • Colorless, low-relief phenakite or chrysoberyl crystals

Hydrothermal Growth Visual Characteristics

  • Fingerprints & veils
    • Note: Extra time and care needs to be taken as they look similar to natural gemstones
  • Chevorn-type growth zoning or wavy growth planes
  • Phenakite or chrysoberyl crystals, gold rods and platelets
  • White particles randomly scattered or  forming ‘comet tails’ or stringers
  • Seed plates in Biron material
  • “Nailhead” or spicule inclusions

Flux growth and hydrothermal growth synthetics are solution based processes and are generally slower and much more expensive to produce compared to melt process synthetics.

For flux growth process powdered ingredients is combined with flux in highly heat-resistant container called a crucible.  Then very high temperature is applied so the flux melts and dissolves the powered ingredients to form a chemical solution.  As the solution cools the synthetic crystal is formed.

For hydrothermal growth process heat and pressure is applied to a mixture of water, seed crystals and crushed chemical compounds.  When chemicals dissolve they rise to the top.  Then when the ingredients cool down, they start gathering around the seed crystals to build a large synthetic crystals.

Flux growth is usually used to produce more expensive synthetic corundum which is the family name for rubies and sapphires.

Hydrothermal growth is popular method for synthetic beryls which is the family name for emeralds.

There are other processes which make other synthetics gemstones but for this blog post I am focusing on only big three gemstones, rubies, sapphires & emeralds.

Imitation Gems

As defined earlier imitation gems are either natural or manmade material that takes the place of a natural gem.  Imitation gems can be made from a ‘variety of materials.’   The most common materials is listed below:


Glass can imitate gems of all colors as well as colorless ones.  Very common to see it imitate cut rubies, sapphires, emeralds, diamonds or any other gemstone – transparent or opaque.

Surface appearance is often enough to separate glass imitation from ‘high’ mohs scale (hard) gemstones.  Its facet edges are generally more round, and facets can sometimes be concave.

Glass jewel is also more commonly molded rather than cut so its surface can have pitted and uneven with ‘orange peel’ effect which is a result from mold process.

Glass also feels ‘warm’ to touch because it doesn’t conduct heat as well as most crystalline gems

Swirl marks is also common feature in glass which has a pattern linear flow structure.  These patterns are actually layers of slightly different composition which are ingredients that aren’t thoroughly mixed.  Swirl marks might be curved, but are more coarser and less regular than synthetic curved striae.

Gas bubbles is also very common trait in glass which contains large, round, randomly arranged bubbles.  They are usually larger than flame-fusion synthetics and are often aligned along the swirl marks.

If you have a polariscope then it is quite easy to check and distinguish glass with rubies, sapphires or emeralds as these gemstones are ‘double refractive’ while glass is ‘single refractive.’   Sometimes under polariscope, a glass imitation often shows snake-like bands.

Assembled stones

An imitation gem can also assemble together into two or more pieces of material which are either fused or cemented together. Two pieces make it a doublet, three a triplet.  The components can be made with various materials including natural, synthetic or imitation versions of gems other than the ones being imitated.

For corundum, doublets are the most common and they usually made with a thin crown of natural sapphire at the top with a flame-fusion synthetic ruby or synthetic sapphire base at the bottom.  You can identify them by looking for the separation plane and color difference between the layers.  They also typically have natural inclusions in the crown and flame-fusion type inclusions in the base.

Some assembled triplets imitate emeralds with actual natural gem materials at top and bottom with colored glass or some material providing the imitation’s green hue.  For emerald imitation usually a layer of green cement is between a crown and pavilion of pale beryl.  The natural portions have beryl’s refractive index (RI) and birefringence and might also contain natural inclusions.

Best way to detect assembled stones is by looking at them from the side, which you can usually see the place where the crown and pavilion are joined together.  Most assembled stones are mounted in bezel settings to hide their separations planes.


Plastic is versatile material which can imitate many gem materials which are transparent, translucent, organic or phenomenal.  Plastic’s luster is similar to the luster of many organic gems, so it’s used most often to imitate them.   But it is not very durable and it melts during any repair work and it is very soft so it scratches easily.

Under magnification, gas bubbles in plastic appear in variety of shapes.  Like glass, plastic jewelry usually also has concave facets, rounded facet junctions and orange-peel effect.

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