Treated vs Untreated Gemstones: What You Need to Know About Treatments

Quick Answer

Nearly every other gemstone in the market has undergone some type of treatment — heat treatment, oiling, irradiation, fracture-filling, or dyeing. Most of these processes are common and accepted in the trade, provided they’re honestly disclosed to the buyer. The real issue isn’t the treatment itself, but hiding it — and a treated gemstone’s price should be lower accordingly.

Introduction

Whenever it comes to buying a gemstone, most buyers only ask whether the gemstone is “genuine” — but an equally important question often gets missed: has this gemstone undergone any treatment? A gemstone can be entirely natural and still be treated — that is, the question of genuine versus synthetic is separate from the question of treated versus untreated. This guide explains which treatments are commonly used, which ones are considered acceptable, and what to ask about them when buying.

Heat Treatment: The Most Common Process

Heat treatment is the most widely used process in the gemstone trade, particularly for ruby and sapphire. It involves heating the gemstone at a controlled temperature to improve its colour and clarity. This process is often permanent, and can sometimes even be difficult to detect in a lab test, yet it’s widely accepted across the trade — provided it’s clearly disclosed on the certificate and at the time of sale.

Oiling, Irradiation and Fracture-Filling

• Oiling: This is the most standard process for emerald. Emeralds commonly have fine fractures reaching the surface, which are filled with cedar oil or similar oils to improve clarity. It’s so common in the emerald trade that almost every natural emerald undergoes some degree of oiling. The oil can fade over time, so re-oiling may occasionally be needed.
• Irradiation: This is used to develop or enhance colour. The most common example is blue topaz — almost every blue topaz available in the market has undergone irradiation followed by heat treatment, since naturally occurring blue topaz is extremely rare.
• Fracture-Filling: Used to make lower-grade ruby’s clarity look better, this involves filling the gemstone’s cracks with glass or resin. Such glass-filled gemstones need special care — they must be kept away from ultrasonic cleaners or steam cleaning, as these can affect the glass filling.
• Dyeing: Used in porous gemstones to make the colour appear deeper or more even.

Hiding Treatment Is the Real Problem, Not the Treatment Itself

It’s important to understand that treatment itself isn’t dishonest — it’s an established, widely accepted trade practice that increases gemstone availability and keeps prices lower than untreated stones. The real fraud happens when a seller deliberately hides treatment information and sells a treated gemstone at an untreated gemstone’s price. So when buying, asking a direct question about treatment and checking for its confirmation on the certificate is just as important as checking for authenticity — you’ll find more on this in our Understanding Your Gemstone Report guide.

Quick Facts

Treatment	Common In	Purpose
Heat treatment	Ruby, sapphire	Improving colour and clarity
Oiling	Emerald	Filling surface fractures to enhance clarity
Irradiation	Blue topaz	Developing a deeper colour
Fracture-filling	Lower-grade ruby	Filling cracks to show better clarity
Dyeing	Porous gemstones	Deepening or evening out colour

Expert Tip: Don’t be put off by oiling when buying an emerald — it’s normal. Just ask the seller whether the oiling is “Minor” or “Significant” (this grading is often noted on the certificate), as it gives you a better sense of the gemstone’s quality and price.

Buying Advice

Since correctly understanding treatment information and assessing its impact on price requires experience, it helps to get quotations from different sellers and compare their treatment details — get in touch with us for help with this.

Key Takeaways

• It’s common for most gemstones to have undergone some type of treatment.
• Processes like heat treatment and oiling are widely accepted in the trade.
• Treatment itself isn’t wrong — hiding it is the real fraud.
• Treated gemstones like glass-filled ones need special care.
• A treated gemstone’s price should be lower than a comparable untreated one.

Conclusion

Treatment on a gemstone is normal — the problem arises only when it’s hidden. When buying, ask directly about treatment, check for its confirmation on the certificate, and assess the price accordingly — that’s the hallmark of a smart purchase.