What To Look For When Choosing A Gemstone
In this section I have tried to touch on a few basic things you need to know and look for when choosing a gemstone. Each of these things are entire subjects in their own right and there are some very good books available and information on the web should you wish to know more. It is advised that if you are going to spend decent money on a gemstone, do some research first.
Being able to differentiate between a poor quality gemstone and a fine gemstone is a skill that can serve you well and will in all likelihood save you money and frustration. Like all things, its experience that counts and the more gemstones you look at the better you get.
Before we begin anything, first some basic terminology.
TABLE : The top flat surface of the stone.
CROWN : The top part of the stone.
GIRDLE : The belt or band that goes around the middle of the stone.
PAVILION : This is the bottom part of the stone.
Its All About Light
This is what it all boils down to... light! The essence of the gem cutter's art is to get as much light as possible to return back up through the top of the stone to your eye.
This stone is good. The angles are correct and light returns back out the top.
This is what you want! You want the light entering down through the table and crown to reflect off the pavilion facets, bounce around and exit back out the top. The more light that does this the better and more brilliant the gemstone will be.
You can also see that the proportions are more pleasing to the eye. They look right. Compare this to the examples below where the angles are too shallow and too steep.
The stone is too shallow. The angles on the pavilion are wrong. Light escapes out the bottom.
This will create the dreaded "WINDOW".
This stone is too steep. The angles are incorrect and light escapes out the bottom.
This will create the dreaded "WINDOW".
So, as you can see the correct angles on the pavilion and crown affect how much light is returned and thus its brilliance. Now, just to complicate matters, each stone type (quartz, topaz, garnet, tourmaline, diamond, etc) has a different set of "critical angles" which determine the optimal angles to return the most light.
Unless you're planning on cutting a stone yourself you don't really need to worry about what these critial angles are, only that they exist. It's something that the gem cutter needs to concern himself with as it directly affects the designs that can be used on a particular type of stone and how well they perform. So long as the design has been optimised for that stone type there is no problem.
Shape and Design
In the commercial mainstream, gemstones are limited pretty much to a standard handful of designs as determined by market forces. With bespoke handcut gems, this situation is very different. Today's gem cutter has access to a great many designs, ideas and information along with specialised computer programs like "GemCad" that allow us to design our own unique cuts. This is a great way to experiment and create quite interesting and gorgeous works of gem art. We can fine tune our designs so they perform as brilliantly as possible and bring out the best that the stone has to offer.
Windows - What is a Window?
So what happens when a stone has been cut with incorrect angles? You get what's called a WINDOW or WINDOWING effect, so named because it lets the light through.
This is probably the single easiest and quickest test you can do to determine whether you've got a good stone or a bad one!
Take the stone and place it over some writing, like a newspaper. Next, looking directly down through the table (top) of the stone do you see the writing? Is there a "window"? You'll know it straight away. The following is an example showing a commercially cut smokey quartz. Note the obvious window with the text easily seen.
Light escaping out the bottom of the gemstone impacts it's performance, ie. the brilliance, fire and scintillation. The gemstone looks lifeless, flat and dull. Compare these next two stones... chalk and cheese. Which do you think is the handcut bespoke gemstone?
One last point on "windows" - pretty much any stone, commercial or bespoke cut will, when tilted or viewed at an angle, exhibit some degree of windowing through the side of the pavilion. Certain stones and designs are more prone to this then others. This is normal and for the most part unavoidable. What we are concerned with is the windowing effect when we are viewing the gemstone directly straight down.
Slight windowing can be seen in this citrine gemstone when viewed from an angle. This is acceptable.
Pregnant Goldfish Belly
Another simple way to tell whether you have a commercial cut is to simply look at the stone and ask the question... does it look like a pregnant goldfish?! This particularly applies to oval shaped stones and the description is most apt.
Remember that the main aim of the commercial cutter is to maximise yield. Stones are sold by weight (carats) so the more stone they have, the heavier it is, the more money they make. These goldfish cuts are very prone to windowing as you can see in the following example... all the light just goes straight out the bottom.
Quality of the Cut
This is where a handcut bespoke gemstone comes into its own. The finished gemstone should be sharp and crisp looking, the polish perfect and scratch free. The overall appearance is one of quality and fine workmanship.
Meet points are simply the points where facets meet or intersect. In a finely cut gemstone, these meet points are as precise and accurate as possible. In commercial cut stones the meet points tend to be a bit more sloppy.
Again, a picture is worth a thousand words.
The facets meet at nice, crisp points.
The facets don't quite meet at a point.
Inspecting a Gemstone
If you are going to spend alot of money on a gemstone, have a good look at it first. The jeweller or shop assistant should have a special magnifying glass called a "loupe" available. Don't be afraid to ask if you can use it to better inspect the gem.
Flaws and Inclusions
Look for any flaws or inclusions that might be present in the stone. Often stones can have internal flaws that are not easily visible at a quick glance. Its only later when you are at home and having a good close look at your purchase that you realise there's a crack or large veil in the stone that you didn't see when in the shop. Avoid the disappointment and really check that stone out first.
With the gemstones that I cut, I try my best to identify and describe any flaws or inclusions that might be present in the stone and give an indication as to how significant they are. Sometimes they are very very minor and barely noticable, other times they might be more so. Generally I try to cut my gems as clear, clean and flawless as possible.
However, not all inclusions are detrimental or flaws. Often there are natural inclusions such as "needles" in a gemstone. In this example, an O'Briens Creek topaz is shown that has a single needle inside it. These needles are formed from different minerals, such as rutile. Rather then being a negative, people often look for these as a sign of a genuine stone and not an imitation. They also add something interesting to the stone and can very often be quite beautiful in their own right.
Oh, and another thing about inspecting a gemstone... those overhead halogen lights they have in the shops will make anything dazzle and sparkle like crazy, even a lump of clay. Try to view the stone in more natural lighting if possible. If you can view the stone outdoors, position yourself so the sun is behind you shining over your shoulder when you look at the gem.
Some stones don't like artifical lighting, like tourmaline for example. Fluorescent and incandescant lights can make certain stones appear muddy and dull or even slightly alter the colour. Again, try to view the gemstone in a range of different lighting, including perferably good old daylight.
Colour is a science in and of itself and can play a very large and often subtle role in determining the fineness of a gemstone. The three main terms are :
HUE : The actual "colour", eg. red, blue, green.
SATURATION : The richness or vividness of the hue.
TONE : The lightness or darkness of the hue.
At the risk of oversimplifying a complex subject - trust your eye. Be wary of gemstones that are so dark you cannot see through them and they appear to "swallow" the light and there is little brilliance. Garnets are a common one for this.
Synthetics and Imitations
Within the marketplace one must be very aware that synthetic and imitation gemstones exist and do so in great quantities in certain markets and unfortunately the potential to be defrauded is there. Always buy your gemstones from a reputable dealer or jeweller.
With many of these imitations it can be very difficult to tell them apart from the genuine item and they are often made to imitate the very finest of their type. Even professional gemlabs can have difficulty in identifying a fake. Remember the caveat : BUYER BEWARE!
Imitations have been around for along time. In 1888, French chemist A.V.Verneuil succeeded in synthesizing rubies. In 1910 synthetic sapphires appeared. Today many people have heard of YAG and CZ (cubic zirconia - not to be confused with Zircon which is a completely natural and desirable gem). There is nothing wrong with synthetics and imitations so long as they are designated as such and they do have their role in the market. Vitually every natural gemstone has it's imitations : diamonds, sapphires, rubies, emeralds, amethysts, citrines, etc... even pearls and opals.
Gemstone treatment is a very common occurence and is one of those things that invokes alot of debate in the industry. In short, gemstone treatment is done to improve the quality and marketability of the final "product".
The treating of gemstones to improve their colour is as old as the custom of wearing stones itself. It probably first started when someone accidently dropped a stone into a fire and upon removing it found that it had altered the colour. Using fire in this manner is the traditional way to treat many stones but has been superceded in large part by the controlled heating in special ovens. This method has wide acceptance in the industry.
The types of treatments are many and varied, some are looked upon favorably and others not so. Some treatments are done ubiquitously to certain gemstones to improve colour and remove or mask impurities and flaws thus dramatically altering its appearance and consequently the value. Heating, oiling (emeralds in particular to fill the cracks), irradiation, lasering, dyeing, acid, berrilium are common forms of treatment.
For certain stones in the marketplace, particularly the more expensive varieties like sapphires, rubies and emeralds, treatment is the norm. Alot of debate centres around disclosure to the buying public of any treatments done to the stone as well as the distinctions between "treatments" and "enhancements". Industry and governmental guidelines can be unclear and in some cases completely lacking. Treating stones is relatively cheap and is done on a large scale, turning inferior stones into something more marketable. This all impacts on a gemstone's value and the industry at large.
Generally speaking, an untreated stone of fine quality should demand a higher price and premium when compared to a similar stone that obtained its "quality" via some manner of treatment. Fine untreated stones of any variety are getting scarcer by the day and harder to come by.