Published in the Jewellery Business magazine | February 2026
Everyone loves a gemstone that sparkles with brilliance and colour. Yet, most mined or synthetic gems do not reveal this beauty in their natural state. Rough stones are often dull, cloudy, or fragile, requiring not only cutting, faceting, and polishing but also treatments that captivate the eye and imagination. From enhancing colour to improving clarity and even strengthening a gem’s structure, treatments have become widely accepted and an important part of the jewellery world. They allow more people access to beautiful gems, which would have otherwise been unremarkable or discarded due to their low gem quality.
Necklace made of drilled rough low-quality light brown (Coffee diamonds) diamonds.
Photo courtesy W. Carter/Wikimedia Commons
The practice of enhancing gemstones is not new—it has been part of human history for thousands of years. To improve appearance and mask imperfections, ancient cultures experimented with techniques like oiling, dyeing, and heating gemstones. While Pliny the Elder (23–79 CE) in his encyclopedic work Naturalis Historia, first noted how many gems were dyed, foiled, or artificially coloured to improve their appearance and deceive buyers, the practice itself goes back thousands of years.
Gems have been experimented upon with not just surface or cosmetic enhancements, but also internal or more permanent and structural treatments that improve durability and clarity of the gemstones. Keeping this in mind, let’s look at gem treatments over the ages.
Oiling
The practice of oiling emeralds likely began in ancient Egypt more than 2,000 years ago, pre-dating Pliny’s notes, a method still used today to fill fractures and improve transparency. This is a traditional process that fills surface-reaching fissures to improve clarity and appearance. After careful cleaning, the stone is immersed in natural cedarwood oil—sometimes under gentle heat, vacuum, or pressure—to allow the oil to penetrate. This reduces the visibility of cracks by matching the stone’s refractive index. While effective, the treatment is not permanent, as oils can dry out or be removed over time, sometimes requiring re-oiling.
Waxing
Waxing gemstones is one of the oldest treatments, practiced for centuries on porous stones such as turquoise, lapis lazuli, and jade to enhance luster and conceal surface flaws. The technique dates to ancient civilizations, where simple natural waxes were used.
Dyeing, staining, and painting
Roman artisans often used plant-based dyes and metal salts to intensify pale stones like chalcedony or agate. Agates were boiled in honey and then heated to darken the banding. Dyes were commonly used in porous gems like coral, turquoise, and agates. Emeralds and spinels were stained with red or green dyes while thin films were painted at the back of the stones to enhance colour or brilliance.
Dyed Pearls
Photo courtesy W. Carter/Wikimedia Commons
Sugar and acid treatment
This treatment was mainly applied to black nephrite (Jade). It involves immersing the stone in a sugar solution, followed by acid exposure to deepen and enrich its black colour. Since it significantly alters the gem’s natural appearance, proper disclosure is essential in the gemstone trade.
Foil backing and surface coating
This method has been practiced since the Middle Ages, when gem cutters used thin foils of gold, silver, or copper placed behind gems—especially garnets, emeralds, and glass imitations—to enhance their colour and brilliance. Thin films and coatings were also applied to stones such as quartz, topaz, and diamonds to create iridescence or improve hue. While these methods were once purely mechanical, modern advances have introduced nanotechnology coatings, where ultra-thin, transparent layers at the nanometre scale are applied to gemstones. These coatings can produce durable, vivid colours, special optical effects, and improved resistance to wear, representing the high-tech evolution of an age-old practice.
Doublets or composite gemstones
A mention must be made of doublets, which were prevalent and used to deceive or imitate rarer gems. Thin slices of gems were glued with coloured glass, or sometimes a thin foil was placed between the crown and the pavilion, which was then glued together.
Bleaching
Bleaching is a gemstone treatment that uses chemical agents such as acids, hydrogen peroxide, or chlorine-based solutions to lighten or remove unwanted body colour, stains, or inclusions. It is mainly used on organic gems and select minerals to enhance their look. Pearls are bleached to even out surface colour and remove dark spots, while jadeite may be bleached to eliminate brown or dark stains before undergoing polymer impregnation (producing so-called “B-jade”). Coral is often lightened to achieve a more uniform tone, and other organic materials like ivory may also be bleached to reduce discolouration.
While all surface treatments had their benefits and the practices continue today, artisans have sought to experiment with techniques that are more permanent in nature.
Polymer impregnation and resin filling
This treatment is a more modern development, gaining prominence in the 20th century with the introduction of synthetic resins like epoxy. The treatment involves filling surface fractures or porous areas with polymers or resins to improve stability, colour, and lustre. This method is commonly applied to emeralds, jade, and rubies as it improves transparency and durability. While effective, resin fillings are not always permanent and can degrade over time with exposure to heat or strong chemicals. Disclosure is essential, as the treatment can significantly enhance the appearance of lower-quality material.
Heat treatment
The earliest such known treatment was the rudimentary heat treatment of sapphires and rubies, which was likely practiced long before the 1st millennium BCE, as ancient gem cutters in Sri Lanka and Burma discovered that heating could enrich colour and remove undesirable tones. Today, gems can be enhanced to their desired colours with controlled heating. Rubies, Sapphires, Tanzanite, and Amethyst are commonly known to be heat-treated. Discovered in 1967, Tanzanite is only found in a small region of northern Tanzania near the Merelani Hills. Interestingly, the discovery is credited to a Masai tribesman, Ali Juuyawatu, who reportedly came across striking blue-violet crystals on the ground after a lightning-induced bushfire. It’s believed the intense heat from the fire transformed the originally brownish zoisite into the vibrant gem now known as Tanzanite.
Surface diffusion
Surface diffusion is a gemstone treatment in which colouring agents, typically titanium or iron (and later beryllium), are diffused into the outer layer of a stone at very high temperatures. The enhancement affects only the surface, so recutting or repolishing may remove much of the colour. This technique became widely recognized in the 1970s, particularly for producing deep blue sapphires.
A diffusion-treated blue star sapphire.
Photo courtesy Gemsphoto/Wikimedia Commons
Irradiation
In nature, green diamonds are known to owe their colour to exposure to natural radioactive minerals in the surrounding rock over millions of years. Similarly, smokey quartz forms when natural radiation from nearby uranium or thorium deposits alters the crystal lattice of clear quartz. Using advanced technology, this treatment exposes gemstones to controlled radiation to alter or enhance their colour, often followed by heating to stabilize the result. It has been experimented with since the early 20th century (around 1905), but gained wider commercial use in the 1950s, especially for producing blue topaz and green diamonds.
Annealing
Annealing is a process in which controlled heating and cooling stabilize or enhance a gemstone’s colour and clarity. It is often applied as an after-process after treatments such as irradiation in blue topaz, diamonds, quartz, zircon, and others to preserve desirable colours and improve stability, and diffusion in corundum to refine surface colour and distribute the introduced colour elements more evenly. Essentially, annealing acts as the “finishing touch” in several treatments to ensure durability and colour stability.
Ionic implantation
Ionic implantation is an experimental treatment developed in the late 20th century, primarily used on diamonds to alter or enhance their colour by bombarding them with ions. It involves shooting specific ions (particle bombardment) into very specific, controlled depths and areas of the gemstone, allowing targeted colour changes or property modifications with minimal penetration. It is more precise than surface diffusion. While it can create unique colour effects, the technique remains uncommon and is not widely used commercially, making disclosure important when applied.
Fracture filling
This is a treatment where surface-reaching cracks in gemstones are filled with glass, resin, or other materials to improve transparency and appearance. Early forms were reported as far back as the 19th century, but the technique became more commercially significant in the 1980s and 1990s, especially for rubies and diamonds, when lead-glass filling was widely introduced to enhance low-grade material.
Fracture Filling
Photo courtesy GlobalGemology/Wikimedia Commons
Laser drilling
Laser drilling is a gemstone treatment developed in the late 1960s, primarily used on diamonds to remove dark inclusions. A focused laser beam is used to access internal inclusions by creating a channel that is thinner than a hair. The dark inclusions are then bleached or dissolved using acids and heat, thus enhancing the gem’s appearance. This method became widely used in the 1970s. Although effective, it must be disclosed, as it changes the stone’s structure and can impact its value.
High Pressure High Temperature (HPHT)
This treatment emerged in the late 1990s to early 2000s, as a method to improve or alter the colour of natural diamonds—commonly removing brownish hues from type IIa diamonds or creating fancy colours like yellow, pink, or green. It simulates the natural conditions under which diamonds form, making it a highly effective and nearly permanent treatment. Later, HPHT as a process was used in the production of synthetic diamonds and for enhancing their colour afterward. Given its subtlety and durability, disclosure is critical, as HPHT-treated diamonds can closely resemble untreated stones.
Chemical Vapour Deposition (CVD)
CVD was developed in the late 20th century and commercialized in the early 2000s. In the 1980s–1990s, it was mainly applied to deposit thin diamond films on gems or industrial materials, which were marketed as ‘diamond-coated’ stones, though these layers were fragile and easily wore off. Today, CVD produces gem-quality diamonds by layering carbon atoms on a seed surface, in a low-pressure chamber, often followed by annealing to enhance colour and clarity. Since CVD diamonds closely resemble natural ones, disclosure is essential. It should be noted that while HPHT and CVD are considered treatments, they are also widely known processes for creating lab-grown diamonds.
The majority of gems available today have undergone some form of treatment to improve their appearance. Identification requires the use of tools commonly used by gemmologists and/or specialized advanced equipment (used in research labs). Microscopy reveals features like filled fractures through inclusions or bubbles, while UV/Visible spectroscopy detects irradiation and dyeing. Infrared spectroscopy (FTIR) is key for spotting oils, resins, and polymers, especially in emeralds. Advanced techniques like Raman spectroscopy and luminescence imaging help confirm more complex treatments, ensuring accurate identification and proper disclosure.
It is important to detect these treatments as they can have a major or minor impact on value. As such, professional organizations like CIBJO (World Jewellery Confederation) and the Federal Trade Commission (FTC) set disclosure guidelines for gem treatments. Sellers and appraisers carry the responsibility of ensuring transparency and must disclose all treatments that affect value, durability, or appearance. Failure to disclose treatments can mislead buyers, harm consumer trust, and in some cases, be considered fraudulent.
From heating to enhancing colours, oils and resins that conceal fractures to the more advanced technological and nano treatments, these enhancements have become an inseparable part of modern gem trade practice. While many treatments are stable and widely accepted, others remain controversial due to durability concerns or lack of disclosure. As Pliny rightly warns, “There is no fraud or deceit in the world which yields greater gain and profit than that connected with gems.” A gem’s story is not just about where it was mined, but also about the processes it has undergone on its journey to its sparkle.