Assaying: Understanding Gemstone Treatments and Enhancements

Assaying, in the context of gemstones, refers to the systematic examination and testing of a gemstone to determine its identity, purity, and authenticity. More broadly, it encompasses the processes used to treat or enhance gemstones to improve their color, clarity, stability, or overall appearance. This article delves into the world of gemstone assays and treatments, explaining how they work, their impact on value, and what consumers need to know.

Definition

Assaying, in gemology, is the process of evaluating a gemstone. While traditionally it meant verifying a gem's identity and quality, in modern gemological practice, it often includes identifying and reporting any treatments or enhancements that have been applied to the stone. These treatments are aimed at making a gemstone more attractive, durable, or stable, but they can also affect its value and require disclosure.

Key Features of Gemstone Treatments

Gemstone treatments are applied for various reasons, primarily to:

• Improve Color: Enhancing the hue, saturation, or tone of a gemstone.
• Increase Clarity: Reducing or concealing inclusions and blemishes.
• Enhance Stability: Making a gem more resistant to damage from light, heat, or chemicals.
• Alter Appearance: Changing the luster or surface characteristics.

It is crucial to understand that most gemstones undergo some form of treatment. The ethical practice in the gem trade is full disclosure of any significant enhancement.

Origin and History

The practice of treating gemstones is not new. Ancient civilizations likely experimented with heating certain stones to improve their color. For example, evidence suggests heating was used for corundum (rubies and sapphires) and turquoise thousands of years ago. Over centuries, techniques evolved from simple heating to more complex processes like diffusion and irradiation. The development of modern gemological laboratories in the 20th century led to a better understanding of these treatments and the need for standardized identification and disclosure.

Types / Variations of Treatments

Gemstone treatments can be broadly categorized. Here are some common types:

1. Heat Treatment

This is one of the oldest and most common treatments. Heating gemstones can:

• Improve Color: Many gemstones, like sapphires and rubies, are heated to achieve more desirable colors. For instance, heating can drive out undesirable brown or yellow tones in sapphires or deepen the red of rubies.
• Increase Clarity: Heat can sometimes cause inclusions to become less visible or even dissolve.

Commonly treated stones include corundum (ruby, sapphire), tourmaline, amethyst, citrine, and topaz.

2. Irradiation

This involves exposing gemstones to radiation in a controlled environment. It is primarily used to:

• Alter Color: It can create new colors or intensify existing ones. For example, many blue diamonds and some green, yellow, or blue sapphires get their color from irradiation.

Commonly treated stones include diamonds, sapphires, topaz, and aquamarine.

3. Diffusion

This is a surface treatment where elements are introduced into the outer layers of a gemstone through high heat. It is used to:

• Change Color: Elements like beryllium or titanium can penetrate the surface, creating a new color. For example, 'lattice diffusion' can create star effects in corundum or deep blue colors in sapphires and diamonds.

Commonly treated stones include sapphires, diamonds, and some garnets.

4. Filling and Oiling

These treatments are applied to improve clarity by filling surface-reaching fissures or pores.

• Filling: Fractures are filled with glass, epoxy, or other foreign substances. This is common in emeralds (often with oil or synthetic resin) and sometimes in diamonds.
• Oiling: Minor surface cracks are filled with colorless oil or other similar substances to make them less visible and improve the gem's apparent clarity.

Commonly treated stones include emeralds, rubies, sapphires, and diamonds.

5. Bleaching

This process uses chemicals to remove or lighten unwanted colors or improve the clarity of certain gemstones.

• Remove Undesirable Tones: Often used on pearls and corals to lighten them before dyeing or to remove brown or gray tints.

Commonly treated stones include pearls, coral, and sometimes jade.

6. Dyeing

This involves introducing a coloring agent to enhance or change the color of a gemstone, often to mimic more valuable gems.

• Improve Color: Used on porous gemstones like pearls, coral, jade, and agate to create vibrant or uniform colors.

Commonly treated stones include pearls, coral, jade, and agate.

7. Impregnation

This process involves filling the pores of a gemstone with a polymer or resin to improve its durability, appearance, and stability. It is often used for porous or fractured stones.

• Enhance Durability and Appearance: Common in turquoise, jade, and pearls to make them less susceptible to damage and improve their luster.

Commonly treated stones include turquoise, jade, and pearls.

How It's Made (Specific Treatments)

The exact methods vary greatly by treatment type. For heat treatment, gemstones are placed in a kiln and heated to specific temperatures, often for several hours or days. Irradiation uses particle accelerators or radioactive sources under strict safety protocols. Diffusion requires placing the gem in contact with specific elements at very high temperatures. Filling and impregnation involve immersing the gem in a liquid filler or resin, sometimes under vacuum or pressure.

Grading & Quality Standards

Gemstone quality is typically assessed using the 4Cs (Carat, Cut, Color, Clarity). However, the presence and type of treatment are critical factors that influence a gem's value and must be considered alongside the 4Cs. Reputable laboratories provide grading reports that detail any treatments identified. Industry standards require full disclosure of treatments that significantly affect a gemstone's durability, appearance, or value.

Buying Guide

When purchasing gemstones, especially valuable ones like diamonds, rubies, sapphires, and emeralds, always ask about treatments.

• Ask Explicitly: Do not assume a stone is untreated. Ask your jeweler directly about any enhancements.
• Seek Documentation: Insist on a grading report from a reputable gemological laboratory (e.g., GIA, AGS, Gubelin) that details treatments.
• Understand the Impact: Treated stones are generally less valuable than their untreated counterparts, though some treatments are widely accepted and expected (like heat treatment for sapphires).
• Beware of Undisclosed Treatments: Untreated stones of comparable quality are almost always worth more. If a seller cannot or will not disclose treatments, consider buying elsewhere.
• Specific Considerations: For emeralds, ask if they have been oiled or filled, and with what substance (oil, resin, polymer). For sapphires and rubies, ask if they have been heated or treated by diffusion.

Price Range & Value Factors

The value of a gemstone is significantly influenced by whether it has been treated and the type of treatment applied. Generally:

• Untreated Gems: Command the highest prices, especially for rare and high-quality specimens.
• Commonly Accepted Treatments: Such as heat treatment for sapphires and rubies, or oiling for emeralds, result in a lower price compared to untreated stones, but are still valuable. The extent and type of filling for emeralds also impact value greatly.
• Less Common or More Invasive Treatments: Like fracture filling with epoxy, irradiation, or diffusion, can significantly reduce a stone's value compared to untreated or traditionally treated gems.

When comparing prices, ensure you are comparing stones with similar characteristics, including treatment status.

Care and Maintenance

Gemstone treatments can affect their durability and care requirements. Certain treatments can be sensitive to heat, chemicals, or ultrasonic cleaners.

• Oiled/Filled Emeralds: Should not be exposed to high heat or ultrasonic cleaners, as the filling material can be dislodged or damaged. Warm soapy water and a soft brush are usually safe.
• Irradiated Stones: Generally stable, but prolonged exposure to strong light can sometimes cause color fading in certain irradiated gems.
• Dyed Stones: The dye can be sensitive to chemicals and heat, and may fade over time. Avoid harsh cleaning agents.
• General Advice: Always ask your jeweler about specific care instructions for your treated gemstone. It is often best to err on the side of caution and use gentle cleaning methods.

Pros and Cons

Gemstone treatments offer both advantages and disadvantages:

Pros:

• Improved Appearance: Treatments can make gemstones more beautiful and desirable by enhancing color and clarity.
• Increased Accessibility: Treatments make a wider variety of gemstones available to a broader market at more affordable prices.
• Enhanced Durability: Some treatments improve a stone's stability and resistance to damage.

Cons:

• Reduced Value: Treated gemstones are typically worth less than untreated ones of comparable quality.
• Potential Durability Issues: Some treatments can be unstable or susceptible to damage over time or with improper care.
• Ethical Concerns: If treatments are not disclosed, it is deceptive and unethical, leading to misrepresentation of value.

Common Misconceptions

Several misconceptions surround gemstone treatments:

• All Treated Gems are Fake: This is untrue. Treated gemstones are real, natural minerals that have undergone a process to improve their appearance or durability.
• All Treatments are Bad: Many treatments, like the heating of sapphires or oiling of emeralds, are standard industry practices and accepted. The key is disclosure.
• Treatments Ruin Value: While they reduce value compared to untreated stones, many treated gems still hold significant value and are perfectly acceptable for jewelry.

Related Terms

• Enhancement: A broader term that includes treatments.
• Composite Stone: A stone made of multiple parts, often involving treatments like filling.
• Foil-backed Gemstones: An older method where the back of a gemstone was covered with foil to enhance its color.
• Synthetic Gemstone: A laboratory-grown gemstone with essentially the same chemical, physical, and optical properties as its natural counterpart; distinct from treated natural stones.
• Imitation Gemstone: A material that looks like a natural gemstone but has different chemical and physical properties (e.g., glass imitating ruby).

FAQs

What is the most common gemstone treatment?

Heat treatment is perhaps the most common and widely accepted treatment, particularly for corundum (rubies and sapphires) and many colored gemstones like tourmaline, amethyst, and topaz.

Is it always bad if a gemstone is treated?

Not necessarily. Many treatments are standard industry practices and are essential for making certain gemstones commercially viable and beautiful. The crucial factor is whether the treatment is disclosed to the buyer. An undisclosed treatment is problematic.

How can I tell if a gemstone has been treated?

This requires specialized equipment and expertise found in gemological laboratories. A trained gemologist using tools like a microscope, refractometer, and spectroscope can often identify treatments. Relying on a reputable jeweler and a gemological report is the best approach for consumers.

Are treated diamonds more valuable?

Treated diamonds (e.g., irradiated or fracture-filled) are significantly less valuable than natural, untreated diamonds of comparable quality. Even color-enhanced diamonds are generally worth less than natural fancy colored diamonds.

What should I do if I suspect my gemstone has been treated and was not disclosed?

If you believe a gemstone you purchased was treated and the treatment was not disclosed, you should have it examined by an independent, reputable gemological laboratory. If the lab confirms undisclosed treatment, you may have grounds to return the item or seek redress from the seller, depending on their return policy and local consumer laws.