What Are Treated and Untreated Precious Stones? Understanding Treatments, Value and Rarity

 

Few materials carry the sense of permanence found in a natural precious stone. Formed over millions of years beneath the Earth's surface, each possesses a history that predates every hand through which it will eventually pass. Colour, inclusions and crystal structure are not simply characteristics, they are evidence of the conditions under which the stone formed.

That journey, however, does not always end when a precious stone is recovered from the earth.

Many stones undergo treatment before they are cut and set into jewellery. Some treatments have been accepted within the international fine jewellery industry for centuries and are considered a routine part of preparing certain stones for the market. Others are less common and can influence rarity, collectability and long-term value.

Understanding the distinction between treated and untreated precious stones allows a collector to look beyond appearance alone. It provides insight into how a stone reached the form in which it is ultimately encountered.

What Does "Natural" Mean?

The word natural is often misunderstood.

Within the precious stone industry, a natural stone is one that formed entirely through geological processes. Its origin lies within the earth rather than a laboratory. The term describes where the stone came from. It does not describe whether the stone has undergone treatment since it was mined.

This distinction is important because a natural precious stone may also be treated.

A sapphire that has been heated remains a natural sapphire. An emerald that has been treated with oil remains a natural emerald. Neither treatment changes the geological origin of the stone. Instead, the treatment alters aspects of its appearance after formation.

Outside the industry, the terms natural and untreated are frequently used interchangeably. Within fine jewellery, they describe two entirely different characteristics. Understanding that distinction is the foundation for evaluating any precious stone.

 

What Is an Untreated Precious Stone?

An untreated precious stone has not undergone any process intended to improve its appearance after it was recovered from the earth.

Its colour, clarity and overall character remain as nature produced them.

This should not be confused with perfection.

Natural precious stones frequently contain inclusions, subtle shifts in colour and internal characteristics that developed during their formation. These features are part of the stone's identity. In many cases they are also what make one stone recognisable from another.

The rarity of an untreated stone depends entirely upon the species.

Untreated diamonds are relatively common because most natural diamonds are sold without enhancement. Sapphires present a very different picture. The overwhelming majority have been heated before entering the jewellery market. Rubies follow a similar pattern. Emeralds are frequently treated with oil because of their naturally fractured crystal structure.

When exceptional colour exists without treatment, rarity increases significantly.

For this reason, untreated examples accompanied by recognised laboratory reports often attract considerable interest from collectors. They represent an uncommon intersection of nature, quality and preservation.

What Is a Treated Precious Stone?

A treated precious stone has undergone a process intended to improve some aspect of its appearance.

Most treatments focus on colour or clarity, although some are performed to improve transparency or reduce the visibility of naturally occurring fractures.

Treatments are carried out after a stone has been mined. They do not create a natural stone, nor do they determine its geological origin. Instead, they modify characteristics that developed naturally over millions of years.

The reasons for treatment are straightforward.

Nature does not produce every sapphire with vivid blue colour. Nor does every emerald emerge with exceptional transparency. Treatment allows certain stones to reveal qualities that might otherwise remain concealed.

Whether that treatment is considered desirable depends upon the process itself, its permanence and the expectations of the market.

 

How Are Precious Stones Treated?

Precious stone treatments are not universal. Each species responds differently according to its composition and internal structure, resulting in techniques that have been developed specifically for that material. Some treatments refine colour. Others improve the apparent clarity or transparency of a stone. 

Below are six of the most common treatments used within the fine jewellery industry.

Heat Treatment

Heat treatment is the most common treatment used on precious stones, particularly sapphires and rubies.

The stone is placed in a specialised furnace and heated to extremely high temperatures under carefully controlled conditions. This process alters the arrangement of trace elements and microscopic inclusions within the crystal, refining colour and improving apparent clarity.

For example, a sapphire with a pale or slightly greyish blue colour may develop a richer, more even blue after heating. Likewise, a ruby with a purplish tone may display a stronger red hue once the treatment is complete. The exact result depends entirely on the individual stone and cannot be predicted with certainty.

Once complete, the change is permanent. Heat treatment has been accepted throughout the international precious stone industry for centuries and remains one of the most widely recognised treatments.

Oiling

Oiling is most commonly associated with emeralds.

After the stone has been cut and polished, it is immersed in a colourless oil, often under vacuum, allowing the oil to enter naturally occurring surface-reaching fissures. This reduces their visibility and improves the stone's apparent transparency.

The oil does not repair the fractures or strengthen the emerald. Because the treatment is not permanent, some emeralds may require re-oiling over time.

Resin Filling

Resin filling is performed in much the same way as oiling but uses a transparent synthetic resin instead of a natural oil.

The resin fills surface-reaching fissures, making them less visible and improving the stone's overall appearance. Because the resin is synthetic, this treatment is generally considered less desirable than traditional oiling, particularly among collectors.

As with all treatments, disclosure is important.

Laser Drilling

Laser drilling is used on some diamonds to reduce the visibility of dark inclusions.

A fine laser creates a microscopic channel from the surface of the diamond to the inclusion. Acid is then introduced through this channel, dissolving or lightening the inclusion so it becomes less noticeable.

The treatment is permanent and can usually be identified by a trained gemologist using magnification.

Fracture Filling

Fracture filling is occasionally used on diamonds that contain surface-reaching fractures.

A transparent glass-like substance is introduced into the fracture, reducing its visibility by allowing light to pass through more evenly. While the treatment can improve appearance, the filling material may be damaged by the heat generated during jewellery repairs.

For this reason, fracture-filled diamonds are generally considered less desirable than untreated diamonds.

High Pressure High Temperature (HPHT)

High Pressure High Temperature, or HPHT, is a treatment used on certain diamonds to alter colour.

The diamond is placed inside specialised equipment that recreates the immense heat and pressure under which diamonds originally formed. This can remove unwanted brown tones or improve the stone's overall appearance by altering its crystal structure.

The changes produced by HPHT are permanent, although the treatment should always be disclosed.

Irradiation

Irradiation is used to change the colour of certain precious stones, including some diamonds.

The stone is exposed to a controlled source of radiation before being heated to stabilise the new colour. The treatment changes the way the crystal interacts with light, producing colours that would not otherwise occur in the stone.

When performed to accepted industry standards, the process is permanent and the finished stone is safe to wear.

 

Which Precious Stones Are Commonly Treated?

The frequency of treatment varies considerably from one precious stone to another.

Diamonds are unusual in that many are sold without treatment. When enhancements are present, they are typically disclosed through grading reports or laboratory certification.

Sapphires are very different. Heat treatment has become so widespread that untreated sapphires displaying exceptional colour are considerably rarer than their treated counterparts.

Rubies follow a similar pattern. Stones possessing outstanding natural colour without heating are exceptionally uncommon and often command substantial premiums at auction.

Emeralds occupy their own category. Minor oiling has long been accepted within the trade because of the nature of emerald crystal growth. Completely untreated emeralds of exceptional quality are rare.

Understanding these differences is important because the significance of treatment cannot be judged in isolation. It must always be considered in relation to the precious stone itself.

Does Treatment Affect the Value of a Precious Stone?

Treatment almost always influences value, although the degree varies significantly.

An untreated sapphire displaying exceptional colour is generally rarer than an equivalent heat-treated example. That rarity is reflected in its value.

An emerald presents a different situation. Minor oiling has been accepted within the trade for decades and is often expected. Its presence does not necessarily diminish the desirability of an outstanding stone.

Diamonds again follow different conventions. Because untreated diamonds are common, treatments such as fracture filling or laser drilling generally reduce value rather than enhance it.

These examples illustrate an important principle.

Treatment alone does not determine value.

A precious stone is evaluated as a whole. Colour, clarity, cut, origin, rarity and treatment history each contribute to the way a stone is understood within the market.

 

The Layla Kaisi Collection Perspective

Every precious stone selected by Layla Kaisi Collection is considered individually.

Selection begins with the stone itself. Its character. The way it responds to light. The qualities that cannot be manufactured, only discovered through nature.

The house  gives preference to untreated precious stones. Their rarity and natural character reflect the conditions under which they formed, often over millions of years, and remain an important part of what makes them exceptional.

That preference does not exist as an absolute rule.

Certain treatments, particularly those that have long been accepted within the international fine jewellery industry, may be considered on a case-by-case basis. Every treated precious stone is evaluated on its own merits, taking into account the quality of the material, the nature of the treatment and its relationship to the finished design.

A treatment alone neither qualifies nor disqualifies a precious stone. The standard remains unchanged. Every stone must possess the beauty, integrity and presence required of the house.

Transparency forms part of that philosophy. Where a precious stone has undergone treatment, it should be understood rather than overlooked. A collector should know the history of the stone they have chosen and appreciate it in its entirety.

Ultimately, the objective is not simply to source the rarest precious stones. It is to select stones whose character belongs naturally within the work they become.