Sunday, August 7, 2011

Can You Get a Gem Like This? Some Brief Notes on Odds

I periodically get questions like these: can you get a 5mm princess cut blue tourmaline?  Or: do you have a matched pair of 4mm round Ceylon sapphires?  And sometimes that’s a “yes”.  Mostly, though, it’s tough.  To communicate how tough, let’s play a numbers game by multiplying out the possibilities. 

1.      Gemstone shapes: There are 8 basic gem shapes: round, oval, emerald, baguette, trillion, princess, cushion, pear.  There are also lots of odd shapes, most of which don’t fit into stock settings, let’s skip those.
2.      Gemstone sizes: Let’s assume that there are 10 sizes for each shape.  For instance, rounds, trilliants and squares will be 1mm, 2mm, etc, ovals and emerald cuts will be 2x1, 4x2, etc, and baguettes 6x2, 8x4, etc.  Baguettes can also be 8x3 or 8x2, and of course there are tons of in between sizes.  We’ll ignore them all.
3.      Gemstone cuts: there are tons, and they matter at least somewhat.  I.e. it matters for setting if the back of a stone is brilliant cut (shallow) or step cut (deep).  For looks, the surface matters.  Some people like checker top, for instance.  Or no facets on the top, which is called “buff cut”.  Rectangular stones are sometimes radiant cut in the back for more brilliance.  All the square cuts, which I inaccurately lumped under “princess cuts”, divide at least into square, princess, or French cut.  There are dozens of cuts out there, not counting combinations.  But let’s just say there are 2x2 relevant cuts for each gem.  That’s two for the top side, two for the bottom side, meaning 4 in total.
4.      Gemstone colors: This is difficult.  Some stones (peridot for instance) all look nearly the same, whereas others (tourmaline) almost never do.  Some colors are rare (blue and turquoise tourmaline for instance), some popular (royal blue sapphires).  For tourmaline, it would be an understatement to say there are 10 different greens, for peridot, it might be an overstatement to say there are three.  A conservative medium might be to say there are 5 different colors per gem, including shades.  I.e. sapphire might be light, medium to royal blue, midnight blue, or purple.  Fancy sapphire might be pink, yellow, orange, green, white, not including any hues.  Tourmaline might be blue, turquoise, grass, forest, and olive, excluding shades.
5.      Gemstone origins: This doesn’t always matter, but let’s restrict ourselves to when it does.  So we won’t care about amethyst, red garnet, citrine, or other quartz.  We will care about emerald, which can be Columbian, Brazilian or Zambian, for sapphire (which comes from Sri Lanka, Madagascar, Australia, Burma, Tanzania…), ruby (Burma, Afghanistan, Thai…), aqua (Brazil, African…), spessartite (Tanzanian, Kenyan, Nigerian…), tourmaline (Brazilian, African…), etc.  With these and other gems, origin matters because of color, quality, and of course, price.  I am going to settle on an average of 3 origins per gem.
6.      Quality: obviously this is very important, but the quality of a gem can range so vastly that I will exclude it.  Let’s say that in general, you want the medium to nicer stuff.

Blue Apatite and Green Zircon Mixed Shapes
Now let’s multiply the odds of finding your gem:
8 (shapes) x 10 (sizes) x 4 (cuts) x 5 (colors) x 3 (origins) = 4800 possibilities

So the odds of finding your gem are an average of 1:4800 for EACH gemstone in at least these categories: sapphire, ruby, emerald, tourmaline, spessartite, tsavorite, alexandrite (the odds will be a little less there, but of course you have to find it in the first place), aquamarine, spinel, and I don’t even know what else. 
Different Kinds of Ceylon Spinel
1.      Most gems are cut according to the shape of the rough, other cuts are uncommon (I’ve never seen a spinel or a spessartite or a tsavorite cut as a baguette).
2.      Certain stones are cut for color retention (so it is hard to find a brilliant cut Ceylon sapphire).
3.      Many gems are cut for maximum size (which is why princess cuts are hard to find).
4.      Some gems don’t exist in certain sizes, or are extremely rare (it is hard to find very small topaz, and hard to find very large alexandrites or rubies).
5.      Some origins are rare.
6.      Matched pairs make for two needles in a haystack, not one.
7.      Untreated gems (in some cases) are rare.
8.      Reminder: we totally excluded the category of quality.

All this affects the odds, mostly by way of increasing them.  The odds of finding a true padparadscha sapphire (meaning Ceylon origin and real salmon color) in a size larger than 2 carats are very small.  Recently a customer asked for a 1 carat round alexandrite of 6mm or larger.  You know what the alexandrite dealer said?  It will be 1 carat, but it isn’t going to be round.
So yes, you can keep asking me to find you certain stones.  I seem to be producing an ever increasing variety of gems (even I am surprised).  But be flexible.

A Few Different Australian Sapphires

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