What makes a sapphire a good sapphire?
Blue is the colour of the ocean, a summer sky and a winter night so no surprises then that sapphire rings outstrip emerald rings and ruby rings in popularity. So what makes a sapphire, a good sapphire? A rich blue bright with a lively appearance and good clarity; not heavily included.
Sapphires and rubies belong to the family of corundum. Corundum is the second hardest gemstone to diamond and it’s found in Australia, Kenya, Madagascar, Myanmar, Tanzania, Thailand and Sri Lanka. I am going to focus on blue sapphires for this blog but sapphires can be in all colours except for red.
Below is a dainty sapphire ring set in 18 ct white gold. For more information about it follow the link.
Blue sapphires gain their colour from a combination of Iron and Titanium. There are a lot of different types of inclusions in gemstones. Inclusions can be either liquid, gas or crystals, they were trapped in the gemstone when it was formed. The possibilities of inclusions are endless and sapphires are no exception, below is a brief look at the types of inclusions that are found in sapphires from the particular localities. So if you have a sapphire ring, take out a magnifying glass and see if these are similiar to what you have in front of you.
What are typical sapphire inclusions?
Indian ( Kashmir) Sapphires: These can look milky due to very small inclusions: Colour zoning, Zircon crystals, Stress fractures and Negative crystals.See the below image of a kashmir sapphire reprinted by permission of GIA.
Myanmar-Burmese sapphires:They can be dark but generally have a good colour. There can be long inclusions; rutile and apatite, Convoluted feathers, Silk and Hexagonal colour zoning.
Thai sapphires:These have different colour zoning with inclusions of silk, feldspar, hornblende, spinel and uranium.
Sri Lankan sapphires:Sapphires feature crystal inclusions of different types and healed fractures that can have the appearance of fingerprints.Image below is an example of a fingerprint inclusion: re-printed by permission of GIA.
Cambodian sapphires:These can show red crystals inside and crystals that have healed fractures surrounding them.
USA sapphires from Montana:Montana saphhires have crystal inclusions such as garnet,rutile, calcite and pyrite.They show hexagonal colour zoning.
Australian sapphires: They can be very dark, looking almost dark blue, green or black.They exhibit strong colour zoning, and crystals with haloes.
For more examples of the inclusions that can be found in Sapphires, follow this link to the GIA website:
How are Sapphires treated?
Treatments: Both sapphires and rubies are often heat treated to improve the colour even of a synthetic one. A lot of sapphires are what is called “diffusion treated” to add colour to poorly coloured sapphires. Some fractured sapphires may be filled. The stones are coated with a compound and then heated to very high temperatures to induce the colour. In blue sapphires it is iron and titanium that causes the blue colour. The compounds are only penetrated to a fraction of a millimetre.
Can you tell if your sapphire is synthetic?
Well you might not be able to tell! There are two ways synthetic sapphires are made; a method called verneuil flame-fusion and a system called flux melt. It is far too complex and scientific to get into how they are made but here are the signs that you might have a synthetic sapphire. Verneuil flame fusion sapphires have growth lines, these are different colours where the sapphire “grew” they are curved as opposed to angular. There can also be gas bubbles present.
To complicate matters the synthetic sapphire could also then be ‘heat treated’ to give the appearance of natural sapphires so there can be evidence of healed fractures and a reduction of curved growth lines. Flux melt sapphires can have platinum platlets, angular growth zones ( which natural sapphires can also have) and flux particles in comet like patterns. Cavities filled with flux and healed fractures.
This should give you an idea as to what to be looking for when you are considering buying a sapphire ring but above any considerations of value, it is more important that you buy what you love! While i admire the deep blue of the most expensive sapphires I am drawn to the deep dark night sky sapphires like this one below that is not deemed as valuable.