Gemstone Treatments Explained: What Your Certificate Is Telling You
"Natural" on a gem certificate means the stone formed in the earth. It doesn't mean untreated. A natural sapphire can still be heated, and a natural ruby can still be glass-filled. Below, we explain each treatment using the exact wording from real IGTL laboratory reports for stones in our collection.
Quick reference: certificate wording and what it means
| What the certificate says | Gem | Meaning | Effect on value | Care needed |
|---|---|---|---|---|
| "No indication of heat treatment" | Sapphire, ruby | Unheated: colour is as nature made it | Highest. Fine unheated stones are rare | Normal care |
| "Indication of heat treatment" | Sapphire, ruby | Heated to improve colour or clarity. Permanent and widely accepted | Lower than an equivalent unheated stone | Normal care |
| "HT … indication of heating. Moderate residue observed" | Ruby | Heated, with some foreign material (residue) left in fissures | Lower than clean heated stones | Avoid strong heat |
| "Indication of glass filling" | Ruby, sapphire | Cracks filled with lead glass to hide them and improve the look | Much lower. A budget product | Avoid heat, acids and ultrasonic cleaners. Tell any jeweller before repair |
| "Heat treatment / beryllium diffusion treatment" | Sapphire | Heated with beryllium so it diffuses into the stone and changes its colour | Much lower. A major treatment | Normal care, but always disclose when reselling |
| "Indication of minor colourless oil" (e.g. F1) | Emerald | Fissures filled with colourless oil to improve clarity. Very common | Minor oil: small effect. More oil: lower value | No ultrasonic or steam cleaning, no harsh solvents |
| "No indication of fracture filling" | Coral | Not filled or reconstructed | Normal | Soft stone; avoid acids and perfume |
| Species "Quartz" (Quartz Cat's Eye) | Cat's eye | A cat's eye effect in quartz, a different, much cheaper mineral | Far below chrysoberyl cat's eye | Softer stone |
| Species "Chrysoberyl" (Chrysoberyl Cat's Eye) | Cat's eye | The traditional, valuable cat's eye (Lehsunia) | High | Normal care |
| "Fresh Water Pearl" / "South Sea Pearl" | Pearl | The pearl type, as named by the lab | Freshwater is the most affordable | Soft; keep away from cosmetics |
The main treatments in more detail
Heating: the most common treatment
Heating rubies and sapphires to high temperatures improves their colour and clarity. It's permanent, it has been practised for centuries, and the trade accepts it. It still has to be disclosed, because an unheated stone of the same look is rarer and costs more. In our own yellow sapphires, for example, unheated Sri Lankan stones were priced at roughly ₹36,000–62,000 per carat, while heated stones of similar size ranged widely below that. See Yellow sapphire price per carat.
Glass filling: a budget option, but know what you're buying
In glass-filled (lead-glass-filled) rubies and sapphires, the stone's cracks are filled with glass to make it look cleaner and brighter. These stones are much cheaper, but the glass can be damaged by a jeweller's torch, by acids and even by some cleaning products. They're generally not chosen for astrological purposes. If you buy one, keep it away from heat and chemicals, and always tell a jeweller before any repair or resizing.
Beryllium diffusion: a major colour treatment
Here, the sapphire is heated together with beryllium, which diffuses into the stone and changes its colour, often deep into the stone. It's a much stronger treatment than heating alone, and these stones cost far less than heated or unheated sapphires of similar appearance.
Oiling: standard for emeralds
Almost all emeralds have natural fissures. Filling them with colourless oil is a long-standing practice. Reports often grade it as minor, moderate or significant, and the less oil, the better. Avoid ultrasonic and steam cleaners, which can remove the oil.
Natural vs synthetic vs imitation
- Natural: formed in the earth (it may still be treated).
- Synthetic (lab-created): the same material as the natural gem, but grown in a laboratory. It must be called synthetic or lab-created.
- Imitation: a different material made to look like the gem, such as glass or dyed stone.
The certificate's Species/Group and Variety lines tell you what the stone actually is, for example "Corundum / Sapphire" or "Quartz / Quartz Cat's Eye".
How Kumud discloses treatments
Every loose gemstone we sell is tested by International Gem Testing Laboratory (IGTL), Jaipur, and the certificate is shown on its product page. We show each stone's treatment on its product page and, for major treatments such as glass filling or diffusion, in the product name, so you can compare stones fairly before you buy.
Frequently asked questions
Is a heated gemstone fake?
No. A heated ruby or sapphire is a natural stone that has been heated after mining. Heating is common and permanent. It must still be disclosed, and it affects the price.
What does "glass filling" mean on a ruby certificate?
It means the ruby's cracks have been filled with lead glass. Glass-filled rubies are much cheaper and need careful handling: avoid heat, acids and ultrasonic cleaners.
What is beryllium diffusion treatment in sapphire?
The sapphire is heated with beryllium, which diffuses into the stone and changes its colour. It's a major treatment, and these stones are priced well below heated or unheated sapphires.
Is oil in an emerald normal?
Yes. Most emeralds are treated with colourless oil to reduce the visibility of natural fissures. Minor oil is the most desirable level.
What is the difference between quartz cat's eye and chrysoberyl cat's eye?
Both show a band of light, but chrysoberyl cat's eye is harder, rarer and far more valuable, and it's the stone traditionally used for Ketu in Vedic astrology. The certificate's species line tells you which one you have.
Read next: How to read a gemstone certificate.