I. Narrow your Search:
Shop for a color (fashion wardrobe considerations).
Shop for a particular species/variety of gemstone.
Shop by budget.
Shop by serendipity (Wide open- browse and decide).
II. Budget considerations and Guidelines:
1. Don't be unduly influenced by the tags "precious" and semiprecious. These are historical terms. Precious gems are diamond, ruby, blue sapphire and emerald. All other gems are termed semiprecious. A high quality 1½ carat tsavorite garnet will cost more than a lower quality 1½ carat ruby.
2. If your budget is too small to buy the quality you want, of a ruby, sapphire or emerald, consider buying some of the more recently discovered gemstones which are also rare and beautiful. Alternative examples: tsavorite garnet (green), green tourmaline, rubellite tourmaline (red), pink tourmaline, tanzanite (violet blue), spessartite garnet (orange to reddish Orange to orangish Red).
3. If you are planning to have your gemstone(s) set in a piece of jewelry, your budget consideration should take into account the estimated cost of the setting. A very large stone will require a larger, more costly setting than a smaller stone.
III. Value/Price Factors: The "Four C's"- Color, Clarity, Cut and Carat Weight
The above Four C's are listed in order of importance. Color, clarity and cut combine to determine the quality of a gemstone.
With each gemstone type, quality (firstly) and size (secondly) effect price. The effect of quality and size is much greater for rare/high demand gemstone types (e.g. ruby, sapphire, emerald) than for the more common, lower value gemstones (e.g. citrine, amethyst, pyrope and almandine red garnets, blue topaz). Because of this, with the more common gemstone types, you can afford to "think bigger."
1. Color (or the lack of it, in the case of diamond) is the most important determinant of value. With any gemstone type, an intense pure color has more value than a lower color intensity stone with secondary color. An example: an intense (high saturation) red ruby is more valuable than: a lower saturation Red ruby or a high saturation purplish Red ruby.
The above color valuation rule has nothing to do with personal taste and fashion considerations. Feel free to prefer pale (pink) amethyst over purple amethyst. Feel free to prefer purplish Red rubellite tourmaline over Red rubellite tourmaline.
With almost all gems, grey and brown secondary colors are not desirable. There are exceptions, e.g. smoky quartz (grayish Brown, brownish Grey). Too dark or too light ("tone") is undesirable.
Uniformity of color affects value and appearance. Color patchiness is undesirable. Color banding (zoning) is common in certain species of gems (E.g. sapphire, amethyst, citrine) and does not have much of an effect on value unless it is very obvious to the unaided eye.
Light source has an effect on color. Incandescent light makes rubies look better. Fluorescent light makes blue sapphire look better. For many gemstones, natural daylight or artificial light that mimics natural daylight is the best way to view and judge the color grade of a gemstone.
2. Clarity: the degree of visible flaws inside ("inclusions") or on the surface ("blemishes") of a gemstone. With colored gemstones, this determination is made with the unaided eye (without the use of a loupe). Almost all gemstones have inclusions. "Eye clean" is the most desirable. If the inclusions are not obvious, they have little effect on the gemstone's value. Some gemstone types, notably emerald and rubellite (red tourmaline) are very rare without inclusions and pricing takes this into consideration.
3. Cut: This affects the amount of light that is internally reflected out of a stone. If too deep, a stone will have dark areas. You'll also be paying for carat weight that cant be seen in a setting. If too shallow, it will have a washed out "window" appearance.
Good cut also means good proportions between crown and pavilion.
Beware of too much "bulge" on the sides of a stone. You'll be paying for carat weight that can't be seen in a setting.
If a crystalline gemstone has low clarity but attractive and more or less uniform color, it is normally cut en cabochon instead of a faceted cutting style.
4. Carat Weight: Gems are normally sold by carat weight. All other things being equal, a larger size gem will have a higher price per carat than a smaller size gem of the same variety.
Some gems types have different specific gravities (weight per volume) than other gem types and will therefore have different sizes for the same carat weight. A three carat ruby is a lot smaller than a three carat aquamarine .
Place the gem face up between two fingers with light coming from behind you (natural light preferred). Rock your hand slightly from side to side and forward and backward. Do you see a window or large dark areas? Can you see flashes of light coming through the surface of the stone or is it dull and lifeless? Make an assessment of the color based on what you are looking for.
Examine the stone from the top and from the sides. Is it relatively well proportioned and symmetrical? Do the sides excessively bulge? Does the stone appear too deep?
IV. Gemstone Treatments:
Most types of gemstones are routinely treated by "accepted" treatments and therefore, there is no routine disclosure of such treatment. The trade distinguishes between accepted treatments (no routine disclosure required) and treatments that require disclosure and you should, as well. Accepted treatments do not lower the value of gems. The treatments that require disclosure lower the value of gems and the pricing of gems that have undergone these treatments should be lower.
Trade Accepted Treatments (routine disclosure not required):
heating ruby and sapphire
oil, wax and certain resin/polymer impregnation of emeralds. There is still some disagreement on whether all resin/polymer treatment needs routine disclosure
bleaching pearls white
heating of amethyst, aquamarine, citrine, tanzanite. tourmaline, zircon , precious topaz
irradiating blue topaz
waxing jadeite, lapis and other decorative gemstone types
dying onyx black
Gemstone types that are not routinely treated are garnet, peridot, spinel, iolite and chrysoberyl alexandrite.
Treatments That Require Routine Disclosure:
beryllium treatment of sapphire and ruby
glass filling of ruby and sapphire
bleaching and dyeing of jade, polymer impregnation of jade
irradiation of diamonds to produce fancy (colored) diamonds
high pressure and temperature treatment of diamonds to improve their color grade
drilling and resin or glass filling of diamonds
dyeing of stones and pearls
irradiation of chrysoberyl cat's eye to obtain higher grade color
resin/polymer impregnation of emeralds. There is still disagreement on whether permanent non-discoloring polymer impregnation requires routine disclosure.
V. Synthetics Gems, Imitation Gems, Man Made Gems
Disclosure is a must as these will have lower value than their counterparts (synthetics) or the gems they imitate ( man made and imitation gems)
Synthetics: These have the same chemical and physical characteristics as their natural counterpart except they have been made in a lab. Disclosure is a must as these have lower value than their natural counterparts. A layman cannot distinguish between synthetic and natural gems.
Man Made Gems: These are gems that are produced in lab and that have no natural counterpart. Examples: CZ, Moissenite.
Imitation Gems: In this case, a gem with a similar appearance is represented as a gem that it is not. The imitation can be a natural, synthetic or man made gem. The purpose is usually deception. Examples: red spinel for ruby; almondine garnet for ruby; CZ, moissenite or white sapphire for diamond, citrine for yellow sapphire.
VI. Gems That Require Special Care:
Peridot: It is a little low in hardness so care must be taken in setting it, wearing it and cleaning it.
Tanzenite: Same special care as for peridot, for same reasons.
Emerald: A high value fragile gem. Not recommended for everyday wear. Care must be taken in setting it, wearing it and cleaning it.
Pearls: Will be attacked by perfume (before drying) and prolonged exposure to perspiration. Must be cleaned properly and stored properly.
Decorative Stones: These are stones that are not single crystals and hence are porous. They should not be washed with soap as this will penetrate and change their appearance. Examples: Lapis, agates, turquoise.
Diamond, Topaz, Kunzite: A sharp blow, in a certain direction, can cause the stone to break (cleave).