Ruby can be one of the highest-priced, among the others coloured gemstone. The quality of rubies has been consistently rising, which breaks the annual auctions record. The value of rubies is determined by slight differences in colour, quality, and treatment. This article will summarize the difference in treatment and inclusions between heated and unheated ruby. For better-quality stone, the per-carat price of ruby can significantly increase as the size increase. Colour also has been the main factor in affecting the value of a ruby. In the market, the desirable ruby colour is a pure vibrant red to slightly purplish red. The visibility of the inclusion in ruby can also affect its value.
Mixture of these untreated and heat-treated rubies shows a range of darker and brighter red colors. Image Courtesy: Robert Weldon/GIA. Courtesy: Tommy Wu, Shire Trading Ltd.
Unheated Ruby is classified as Natural Ruby that has not been heat treated. These natural rubies are known to be quite easy to identify as compared to the unheated rubies, as it has natural inclusions that are 10 times visible when seen using a microscope. The characteristics of the inclusions in unheated ruby are intact silk needle-like intersecting at 60 degrees angle. Other following properties of inclusions are unaltered calcite and prismatic like crystals.
Characteristics of the 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
Image Courtesy: Buygemstone
Prismatic amphibole crystals Intact Silk needle like Inclusion Intact and unaltered calcite
in Winza Ruby crystal and hexagonal color
Winza Tanzania Natural Unheated Ruby
In 2007 a new gem known as Winza Tanzania Unheated Ruby was discovered in Central Tanzania, Winza ruby mine. Winza mine produces outstanding ruby quality, other gems and corundum within a short period of few months. Winza mine produces corundum in Bicolor and Tricolor gem. One of the unique discovery in the Winza mine was the Mixture of Red ruby and Blue Sapphire. Due to its pure vibrant red colour, Winza Tanzania ruby rarely receives heat treatment hence it is known as being a natural unheated ruby.
Bicolour and Tricolour gem 14.97 carat of ruby from Winza
with a mixture of ruby and sapphire Tanzania is known to be of high price of ruby
Image Courtesy: GIA Image Courtesy:
Inclusions in Winza Tanzania ruby
According to the crystal morphology, the Winza corundum is divided into two types of inclusion which is prismatic-tabular-rhombohedral and dipyramidal. The medium red and dark (orangy) red quality is rhombohedral. On the other hand, the pinkish-red, purplish-red rubies and purplish-red rubies are known as dipyramidal. Research shows that the top qualities of rubies have inclusions such as long-tube fibre like a needle or hair-like inclusion with an orange-brown material that is known as limonite. The lower quality of rubies usually contains an extensive amount of solid inclusions, such as amphibole crystals and fissures.
Inclusions in Winza Tanzania Ruby
Image Courtesy: V. Pardieu
Prismatic amphibole crystals An orange-yellow garnet inclusion Long-tube-fibre needle like or hair- like inclusions.These inclusions are common in top-quality Winza ruby.
Today, it is common for rubies to go through heat treatment. This is because the heat treatment of rubies will enhance the colour of ruby and improve the clarity by removing any inclusions inside, making them less visible. This treatment rarely diminishes the value of the ruby however, there are different levels of heat treatment that may be classified from slight to quite extreme at a very high temperature. The value of ruby that is being treated at an extreme temperature may diminish.
Inclusions in Heated ruby
Dotted Rutile Silk Fractures with tension halos. Discoid fracture with tension halos Image Courtesy: Richard W. Hughes Image Courtesy: AGSL altered mineral inclusions with rounded “cotton” like.
Image Courtesy: Alberto Scarani
Mong Hsu Ruby
Today, the two primary sources of Burmese Ruby are Mogok and Mong Hsu. Mogok Ruby is a traditional type of ruby that is of high quality. Mong Hsu Ruby is originated from a small town in northeastern Myanmar, formerly known as Burma. The untreated sample of Mong Hsu Ruby typically comprises bicoloured corundum with dark violet or blue to almost black sapphires cores and ruby rims. With heat treatment, the dark blue cores inside the ruby can be converted to red, making the dark-coloured cores invisible. In Comparison, the Mong Hsu Ruby quality is not as high as the Mogok ruby. Untreated Mong Hsu Ruby typically shows the distinctive zoning with dark blue or violet cores, a cloudy appearance, and multiple fractures. As a result, most stones from this deposit are heat-treated at moderate temperature. At the same time, these rubies also received flux treatment to mend fractures. Flux treatment often improves clarity and removes any unwanted dark zones. Therefore, unheated Mong Hsu Ruby is quite rare.
Image Courtesy: GIA
Mong Hsu ruby weighing 6.21 Carats with dark blue zone being heat treated at 800 degree Celsius for 16 mins. This is to reduce the dark blue zone and make it invisible and often need to rely on advanced technology.
Inclusions in Heated Mong Hsu Ruby
Partially healed fissure with a snowflake-like pattern is seen in a flux-heated Mong Hsu Ruby. After going through a chemical analysis and gemologist observation of internal features shows that the origin of this stone was the Mong Hsu. The pattern of the snowflake-like pattern is formed by the crystallization of the glassy flux residue treatment. The partially healed fissure which looks like a snowflake is one of the rare features that has been encountered under research.
Image Courtesy: GIA
Ruby Flux Treatment
Flux treatment is a treatment that has to brings in contact with the material and it will lower to lower the melting temperature of the ruby. A substance such as borax is being added in. This improves the clarity of the ruby. However, because the materials being added in are not natural, the price of flux treatment ruby will be less.
Image Courtesy: GIA
Flux-healed fracture in a ruby that was heated with borax flux. Image Courtesy C. Khowpong
Burmese Pigeon Blood ruby
Historically, the term 'pigeon’s blood' is known for the red to slightly purplish or pinkish-red colour of rubies with a soft glowing red fluorescence. These Burmese pigeon blood rubies are usually found in Mogok Myanmar. This colour effect makes Pigeon Blood Red Ruby gemstone desirable and popular.
The 3.32 Carats Crimson Prince ruby was sawn from a 1.2 gram rough. The colour and clarity is known to be extremely rare Image Courtesy: Robert Weldon/GIA, courtesy of Jeffery Bergman.
How to identify Glass lead glass-filled ruby?
The glass fill most important issue is in the market is the lead glass filling of fractures in rubies they are more browny and opaque. The lead glass-filled ruby made the appearance of the ruby to be transparent and cuttable, which is easily broken. With training and microscope, it will enable people to see the properties of its glass lead ruby. Glass lead glass-filled ruby usually has a flash effect property which is a bright flash and structure of blue and orange fractures. Large Glass bubbles cavities and flattened gas bubble are also seen in lead glass-filled rubies.
Image Courtesy: GIA