Blue sapphire education and questions

[Rad_Fan]

I also became intrigued about this gem due to many recent PS blue stunners and wanted to learn more about it.

This is GIA Heated and I am just curious what you all think about the brownish “cracks” shown between 3 to 6 o’clock. Are they surface reached inclusions, hence less desirable and should be less $?



Also, the “pool” of blue on the pavilion down to the culet looks like a splash of concentrated blue under there, is it dodgy or just common color zoning??

 

[Bron357]

That “crack” could be a healed fingerprint or fissure. What really matters is if it is surface reaching (could be bad for gem stability). You’d need to see a photo where those facets are lit to see if it’s surface reaching.
Colour zoning is common. It reduces price usually. Cutters will normally try and minimize the extent or place it to the outer edge but will save carat weight rather than remove it.
Sapphire cost / value is driven by many factors. Apart from size and quality of cut, first would be treatments. Unheated is usually much more expensive. Heated is next, then heated with residues / evidence of beryllium treatment. Treatments can be minimal or invasive. Unheated / untreated might be $2,000 a carat, Heat only $1,200 a carat, Heat with minor residue $800 a carat, heated with residues and beryllium treatment maybe not even $100 a carat. This is why a lab report matters because to “the eye” these differences aren’t usually noticeable. Origin is also important. A Kashmir or even some Burmese sapphire are worth many times more per carat. Colour / hue and tone are important. A vivid Velvet blue is worth much more than a pastel or inky blue gem. Also price per carat alters as the gem carat weight in creases. A 1.80 carat sapphire might be $2,000 a carat whereas a similar sapphire at 3.10 carats might be $3,000 per carat.
A glass filled beryllium treated velvet blue sapphire of 3 carats might be worth $300 whereas a 3 carat certified unheated fine Kashmir sapphire might be $50,000.
Here are my two. You can see that one has a lighter zone. It’s less noticeable face up than face down.

 

[Rad_Fan]

Thanks for the awesome general guideline on pricing. I've been trying to gather such info.

The one I posted is certified as Heated by GIA. What is the "pool" on blue on the pavilion? It just looks kind of abnormal to me.

AGL lab is preferred to id the treatments. What is the correlation between surface reaching inclusions and treatment for sapphire? Is that similar to that of emerald? Is heat treatment mainly for enhancing color?

 

[Bron357]

The “pool of blue” appears to be a section of colour zoning, it seems that the cutter has decided to “centre” this color variation. The photos arent particularly great. It’s hard to judge the intensity of the zoning. Gems are obviously not set with the pavilion showing so you really need more face up photos to assess the gem.
Heating is used to reduce rutile inclusions (called silk) these can make the sapphire look hazy / translucent. If the lab report says H (a) that is meant to mean low heat, negligible evidence of residue. This is acceptable. H (b) means heat with moderate residue and H (c) means heat with significant residue. Residue is just a way of saying flux filled. If a sapphire is heavily included ie fissures which are surface reaching, flux or glass filling is often used to fill these in. This filling isn’t stable ie pickling (this is an acid used after soldering metal in jewellery to clean it) can dissolve the flux as can heat from a jewellers torch (again when working on the metal setting). Beryllium treatment which is like a colour infusion is more stable but is an artificial way of getting colour. It requires specific lab analysis (it usually can’t be seen with a Loupe or microscope). If a sapphire is heated, it has to be further investigated for either flux filling and beryllium treatment as these dramatically affect value. Obviously an unheated gem cant be glass filled or beryllium treated because both these treatments require high heat. Beryllium treatment is considered heavily treated and barely a “step up” from a lab grown sapphire. You would be much better off buying a lab grown sapphire than a heavily treated natural sapphire. Be aware that when vendors say “natural” they only mean “not lab grown”. Natural does not necessarily mean “no treatments”.
Emeralds are slightly different. Emerald is a type 2 gem. The crystal structure has natural imperfections. Emeralds require more care and shouldn’t be pickled or put in an ultrasonic cleaner. A jeweller will unset an emerald to work on the setting. Emeralds are normally treated with oil. This is considered acceptable treatment. Oil does leech out over time. These days a synthetic filler called Opticon is used. This is permanent. It is a rare and expensive emerald that has a lab report “no evidence of oil or other treatment”.
AGL is the preferred lab for coloured gems (over GIA who specialize more in diamonds). Other regarded labs include Lotus, GRS Swiss lab. You have to be wary of many Asian / Indian lab reports (the type all over eBay and Etsy) as many of these are not reliable, sometimes they are outright fakes.
A suitably qualified gemologist can identify between lab grown and natural and detect evidence of heat treatment and residues. To detect beryllium treatment requires more specialized equipment (additional costs) and to give an opinion on origin (which can have a significant impact on value) you can only really trust the opinion of the top labs. Origin designation requires analysis of both the inclusion types and trace elements.

 

[ordinaryrainbow]

This book extract has an interesting set of tables that set out sapphire pricing. It’s out of date now and sapphire prices have increased significantly since it was published, but it does show the exponential price increase from heated to unheated and as carat size increases.

http://www.ruby-sapphire.com/r-s-bk-prices.htm

I can’t remember if it’s in this extract or another one, but the author doesn’t think it worthwhile to consider colour zoning unless it is apparent from top down or in a 180 degree view like would be seen once the stone is set in jewellery. I don’t know if that view is commonly held, however.

 

[JoseGascon]

This book extract has an interesting set of tables that set out sapphire pricing. It’s out of date now and sapphire prices have increased significantly since it was published, but it does show the exponential price increase from heated to unheated and as carat size increases.

http://www.ruby-sapphire.com/r-s-bk-prices.htm

I can’t remember if it’s in this extract or another one, but the author doesn’t think it worthwhile to consider colour zoning unless it is apparent from top down or in a 180 degree view like would be seen once the stone is set in jewellery. I don’t know if that view is commonly held, however.It is also worth considering triangeles trigonometry when processing, I often use a special calculator https://plainmath.net/secondary/geometry/trigonometry/non-right-triangles-and-trigonometry on a website with mathematical questions.

Thanks, that's just what I was looking for. Unfortunately, there isn't a lot of useful information about sapphires.