When buying a colored gemstone, you want to know that you're getting the best deal for your money. That’s why it’s important to develop a basic understanding of the criteria jewelers and gemologists use to determine a gemstone’s grade and price.
While there is no standardized grading system for colored gemstones, it is common practice to use the same criteria used to grade diamonds, known as the 4C’s. The 4C’s include color, cut, clarity and carat. Additional factors that need to be considered are the durability of a gem and any treatments used.
Gemstone Color
Color is the most important quality in grading a gemstone. A gemstone’s color can be broken into three categories: hue, tone, and saturation.
Hue
Hue refers to the color(s) of the gem. In most cases, a gem will have a primary color (red, blue, or yellow) and a secondary color, which is the result of primary colors mixing together (orange, green and purple). The most valuable gemstones will have a pure color and only slight hues of others.
Tone
A gem’s tone refers to the lightness or darkness of a stone’s color.
Saturation
Saturation refers to the intensity or purity of the hue, ranging from light to strong to vivid. The more vivid the gemstone, the more valuable it is.
Gemstone Cut
The cut of a colored gemstone describes its shape and how it is fashioned. All gemstones are cut by hand and each cut depends on the individual stone. Colored stones have their own natural glow, which is only enhanced by the quality and style of the stone’s cut.
Gemstone Clarity
A gemstone’s clarity grade is based on whether a gem has inclusions (materials trapped inside the gem), fractures, and blemishes (surface imperfections) that affect its appearance and structure. Most natural gems have inclusions. If a stone looks too perfect, it’s been treated or is fake.
Inclusions are ok as long as they aren’t too distracting. Certain descriptions that may be used to grade clarity include: “loupe clean” (no visible inclusions with a x10 loupe or magnifying glass), “eye clean” (no visible inclusions to the naked eye), and “included” (some visible inclusions).
Durability
The Moh’s hardness scale is a 10-point scale used to measure how well a gemstone resists scratches and scrapes. The higher the number, the tougher and more durable the gem. For instance, sapphires and rubies are both ranked a 9 which means they are strong enough to wear every day. An opal on the other hand, only has a hardness between 2.5-4.5 which makes it more susceptible to being damaged.
Treatments or Enhancements
It is a routine procedure for most gemstones to undergo some form of heat or chemical treatment to improve their color and clarity. A stone that is untreated is exceptionally rare and very expensive. Think of a gemstone treatment like putting lipstick on before you leave the house – it helps to “enhance” your overall appearance. Treatments can affect the value of a gemstone, however, and some may do more harm than good.
Common Gemstone Treatments:
Heat treatment
When gemstones are exposed to high temperatures, their color can greatly improve. Common gemstones that undergo heat treatment include sapphires, rubies, amethysts, citrine and aquamarine to name a few.
Oiling
Oiling is commonly used to treat inclusions in emeralds. Certain oils, such as cedar can effectively penetrate cracks to improve an emerald's clarity. Oiled stones need special care to prevent having to clean or remove the oil.
Diffusion
A diffusion treatment involves exposing a gemstone to certain chemicals under extreme heat. This results in richer color but only on the surface layer, so the color might come off with routine cleaning, polish, or repair.
Filling (glass-filled or fracture-filled)
Filling is a process where glass is introduced during the heating process in order to “heal” or seal fractures. This is considered a controversial treatment because it makes severe flaws undetectable to the naked eye. It can also make stones prone to breakage. Filling is known to be used with very low-quality rubies.
Dyeing
Dyeing involves pouring colored dyes into fractured gems to enhance the color. Gems that are frequently dyed include turquoise, pearls, and black onyx. Some dyes can leak out or fade over time if exposed to prolonged periods of sunlight.
Be Smart When Buying Gems Online
With online shopping increasing, there is an increased risk of encountering fraudulent sellers, and that includes those selling jewelry. Here are a few tips when considering buying a gem online:
Verify a seller’s credentials
How long has the seller been in business? Do they have a legitimate website? Are there customer reviews available? Do they have a return & refund or exchange policy?
Don’t be fooled by false advertising
Keep in mind that a “filter” can be added to any picture to make it look better than it really is. This is a trick that overseas suppliers may try to use to move their merchandise. Fraudulent sellers may also use stock photos which capture a rendering of the product, not the product itself. Be on the lookout for watermarks, however faint.
Second-guess the quality
Have you ever come across your dream ring in a jewelry store only to find an “exact replica” for half the price on Etsy or Ebay? If it sounds too good to be true, it probably is.
Let's say you’re looking at a $100,000 emerald ring and a $100 emerald ring side by side. They both have the same green color and carat weight. So, how is it different? One word: quality. The $100,000 emerald is likely an all-natural gemstone with no heat or oil treatments applied, making it flawless. The $100 emerald has probably undergone several treatments to make it look better than it is. Over time, there’s a strong possibility the $100 stone will lose its luster and even appear “milky” in color.
Find a Jeweler You Can Trust
An obvious and key advantage of buying from a retailer is that you can establish a relationship with a jeweler and see a gem in-person. A local jeweler should care about their reputation and be less likely to engage in fraudulent practices.
Don’t be afraid to ask questions
There’s an old saying in the industry, “if you don’t know jewelry, ask your jeweler.” You have the right to know what you are buying. Here are a few questions to ask your jeweler when shopping for a colored gemstone:
Is the gemstone natural (from the earth), synthetic (created in a lab) or simulated?
Buying a colored gemstone is, of course, a matter of preference but you should know whether you’re buying one that is natural, lab-grown or simulated.
For a stone to be natural, it must have been created naturally with no human interference. Natural stones are more expensive because of their rarity and will maintain their value. They tend to look more real and unique because they have natural inclusions (imperfections).
Synthetic stones are produced in a lab but have identical properties to their natural counterparts. They are more affordable and have less imperfections (appear brighter) than natural gems since they are made in a controlled environment.
Simulated stones are created to look similar to natural gems but are made of a completely different substance. Cubic zirconia is a good example. They are the cheapest alternative to natural and synthetic stones.
Has the gemstone been treated or enhanced?
Remember, it’s normal for a gemstone to be treated. However, certain treatments
can dramatically affect a gemstone’s value. You need to ask your jeweler to disclose which treatments were used, otherwise you could be charged a higher price than what the stone is actually worth. A treated gemstone may also require special care so it’s good to know what kind of maintenance (if any) may be needed long-term.
Ask your jeweler for a gem laboratory certificate when making a purchase.
Make sure your colored gems are properly insured so you can wear them with confidence. Find out how affordable a dedicated jewelry insurance policy is.
