There's so many factors, it's hard to decide where to begin. Leaving aside the metalwork and any secondary stones, and assuming a synthetic stone is not what you want, here's some questions/pointers for the sapphire itself:

Untreated or treated? Many sapphires are treated to improve colour and/or transparency. Obviously, stones that are treated are cheaper, but may be more brittle and/or the treatment may not be permanent, depending on how they have been enhanced. In general, mild heat treatment to enhance clarity is safe and totally permanent; titanium diffusion to turn a pale stone into a darker one is essentially regarded as "fake", and since the diffused layer is very thin it may be scratched or polished away should you ever need to re-cut the stone.

What colour shade? Blue in sapphires ranges from pale, greyish "northern sky" to very dark almost black "midnight blue". The most valuable tones are in medium to medium-dark, highly saturated blue and have a minimal amount of other hues (no brown, green or grey, but some violet may be seen as desirable). Valuable does not equal beautiful, though, and if you prefer the paler violetish-blue of many Ceylon stones, no-one can say you are wrong.

Where does the sapphire come from? There is a hierarchy of value - and to some extent of beauty - depending on where the sapphire (purportedly) comes from. At the top sits Kashmir, followed by Burma, Ceylon, Thailand, Madagascar and Australia. Montana sapphires of gem quality are highly prized, but also rare, and don't fall into a "value" hierarchy quite as readily for their other attributes, since they are typically small and relatively light in colour (although usually very limpid and bright). Be careful of deceptive claims by sellers such as "this Kashmir/Burma/Ceylon blue sapphire" seeming to imply that the stone is from Kashmir/Burma/Ceylon. It may not be, but its colour is (according to the seller) that of a typical Kashmir/Burma/Ceylon sapphire. Any claim as to geographic origin of a stone - and consequent premium price - has to be taken with a large pinch of salt unless accompanied by credible documentation.

Who has graded the stone? Lab reports for coloured stones are even more bewildering than for diamonds, since the number and type of treatments that the stone can be subjected to is much broader. At the same time, lab reports are nowhere near as common, also due to generally lower prices of coloured stones compared to diamonds. In terms of credibility, AGTA, Gubelin and GRS-Bangkok are for coloured stones what GIA is for diamonds. AGL/GCAL and GIA are also reputable, if much smaller in volume, although this may change since the closure of AGTA at the end of July 2009. While some of the differences in coloured stones are easier to grade than for diamonds (largely because the grading scales themselves are different), detection of certain treatments to enhance colour and indication of geographic origin require true expertise and expensive equipment. Only you can decide how comfortable you are with the seller's word about his/her merchandise, given the value of the purchase and the extent to which the value depends on the seller claims being true or not. In other words, if I was buying a 3 ct untreated cornflower-blue Kashmir sapphire, I'd want genuine proof of the claims. A fairly priced 1 ct heat-treated dark blue Madagascar sapphire may well stand on its own.

How is the stone cut? Most sapphires are cut - frankly - poorly. Partly this is because the main requirement in the market for a coloured stone is, unsurprisingly, its colour; partly it is because the miner or the upstream trader knows it can get a fair deal more money for a cut stone than for a piece of rough, but has neither the skill/equipment nor the financial incentive to cut it well; partly it is because sufficient buyer education is even less widespread in coloured stones than it is in diamonds. At any rate, the fact remains that it is more likely that a sapphire is cut for weight retention and colour depth than for liveliness and attractiveness of the stone while preserving colour. This tends to put a somewhat disproportionate premium on the (relatively) few stones that are both nicely coloured and well cut.

How big is the stone? Sapphire is heavier than diamond - roughly, a sapphire of the same weight (and cut proportions) of a diamond will appear 10% smaller. In addition, you have to consider that typical cutting proportions of sapphires are deeper than for diamonds, and that sapphires are on average cut with greater attention to weight retention than diamonds. Put all this together, and for a similar outline shape (round, oval, rectangle, ...) you'll need typically 1.2 to 1.5 carats of sapphire to have the same visual size as a same weight diamond. On the other hand, sapphire crystals tend to be larger than diamonds, and stones of 3+ carats are relatively common, with true rarity going from 10 carats upwards.

Apologies for the long post - but these are the six things that would be top of mind for me, and where I'd want some precise answers prior to buying. Of course, this all boils down to the two basic questions for any purchase:

1. Do I like the goods?
2. Do I trust the seller?

If the answer to both questions is yes, the decision is easy.

The are various aspect you need to consider for sapphire - you can browse some of the article on web - which will help you to get the information you were looking for.

This one is ticking all the right boxes for me:

http://rockdiamond.c...5bb557e874b3e87b9ed8

It's whatever the seller decides...

It's vague, like "canary diamond" or "eye-clean". In general, it is taken to mean stones that are of excellent overall quality for the species - colour, clarity and crystal have to be of superior level for the stone to be considered a gem, and treatment/enhancement has to be none or minor. The issue is that none of the above are well defined or consistent across mineral species (an emerald with a few almost invisible inclusions is rare, and may well be considered a gem; an aquamarine with a few almost invisible inclusions is considered second rate - and they are both beryls!)

I love a good sapphire!  I am considering purchasing one in the future to replace an amethyst I have in a ring.  So I admit I am loving this thread and mooching off the info posted!

What kind of a look are you going for with your ring?

OMG!
That is stunning. May I save that in my 'inspiration pics' folder please? I do love it.

OMC, I thought as much re gem quality, but I wasn't sure it didn't have a formal meaning. Thanks.

Jen

Shiba, I love the ring!  I would have thought a sapphire would look too dark set like that, but you pulled it off beautifully!

Mikla

I love your photos Shiba~!!!!!
I also loved the ring- which was designed by Shiba, I might add!!!

Jen, I use the term "Gem Quality" in many ways.
In diamonds it's a wide term (ie industrial versus "gem quality"
But there is no fixed definition....I like OMC's answer too!

Thanks!  
I didn't start a new thread for the reveal, I had just added them into David's "help me select some sapphires" thread.  GL made earrings out of stones from the same parcel and they turned out gorgeous too.  It is actually quite light for a sapphire but I wanted to see into the stone, and see the cutting.  A dark stone might have looked like a blob in this style of setting.  It is a 1.01 square cushion with step-ish cuts.

Mrs. M, you can certainly use the photos.  I have other inspiration pics that were used to design this ring which I would be happy to send you-  I can't take credit for the concept.  It is a W I D E ring, 11mm in the front and 8mm in the back.  I would even go to 13mm with larger mellee or a larger center.

Here are the other pics