Unheated vs heated ruby and sapphire: price premium and report wording

There is no fixed percentage. GIA states that rubies an independent laboratory confirms as unheated command a premium because of their rarity, and Sotheby's puts unheated stones at under 10% of gem-quality rubies; the sources we reviewed suggest the gap varies with colour, size and origin. The only proof is the treatment comment on the report itself, such as "no indications of heating" or, at GRS, "no indication of thermal treatment".

What does heating do to a ruby or sapphire?

Heating is used on ruby and sapphire to improve their appearance. Lotus Gemology defines its code H simply as heat used to improve colour and/or clarity, and GRS distinguishes heating with no residues from heating that leaves residues in fissures or cavities. Heat can also be applied at low temperatures that leave few visible traces, which is one reason detection keeps evolving.

GIA's ruby buyer's guide is blunt: "You should assume your ruby is heated." It advises buyers to ask for treatment information in writing and notes that rubies an independent laboratory confirms as showing no evidence of heat command a premium because of their rarity.

How do laboratory reports word heating?

Seven laboratories, among them GIA, Gübelin, SSEF, CISGEM and DSEF, sit on the Laboratory Manual Harmonisation Committee (LMHC), which publishes standard report wording. Its current corundum sheet (version 6, February 2023) uses two phrases:

• "No indications of heating", abbreviated NH.
• "Indications of heating", abbreviated H, optionally followed by a note that heating was used to modify colour or transparency.

Where heating has left residues in fissures, the LMHC's May 2025 sheet grades them as minor, moderate or significant. Some labs use their own codes. GRS, for example, defines these on its website:

• No indication of thermal treatment: no gemmological evidence of heating found.
• H: heated, no residues.
• H(a): heated, insignificant residues in fissures.
• H(b): heated, minor residues in fissures.
• H(c): a transitional grade between H(b) and H(d).
• H(d): significant, deep-reaching residues in fissures and cavities, including lead-glass filling, which GRS calls "composite ruby".
• H(Be): heated with light elements such as beryllium.

Lotus Gemology uses H for heat, H-FH for heat with fissure healing, H-D for heat with diffusion of external colouring agents and H-GF for heat with glass filling, and uses gold report covers when no treatment is detected. Older reports may show the LMHC's earlier TE scale; a 2010 GIA paper notes that GIA laboratories began using the TE scale on reports that year.

Heat only, flux residues, beryllium and lead glass: why the value differs

Flux-assisted healing

Some rubies are heated with a flux. A 2010 GIA report by Pardieu and colleagues describes the surfaces of the ruby dissolving into the flux and the material recrystallising as it cools, so that fissures partially heal; the treater in that study used borax and silica at about 1,400°C. Residues remain in the healed fissures, and both the LMHC and GRS grade how much is left.

Beryllium diffusion

Diffusion adds a colouring agent from outside the stone. GRS codes heating with light elements such as beryllium as H(Be) and describes the treatment as permanent, while Lotus Gemology does not issue colour types for diffused stones. GIA's ruby buyer's guide states that diffused rubies are worth less than heated ones.

Lead-glass filling

Heavily fractured ruby can be filled with lead glass. GRS reports such material under H(d) as "composite ruby", and Lotus uses a separate code, LGH, for lead glass-type hybrids. GIA states that glass-filled rubies are worth less than heated ones and that filled material should only be cleaned with a damp cloth.

How much more is an unheated ruby or sapphire worth?

We found no current, published premium from a laboratory or auction house that applies across qualities, and multiples quoted online rarely cite data. Credible sources say this:

• GIA: rubies with an independent report showing no evidence of heat command a premium due to their rarity.
• Sotheby's (2026): fine rubies and sapphires of exceptional colour without indications of heating are considerably scarcer than treated ones, and a smaller unheated ruby of extraordinary colour may command more than a substantially larger stone of another variety.
• Richard Hughes, Ruby & Sapphire (1997): May 1995 market memos showed most better-quality Mogok rubies heated at high temperature selling at discounts of up to 40% to unheated stones, with no difference for low-temperature heating; for Kashmir sapphire, some dealers discounted treated stones by up to 30 to 40% while others charged the same.

Those 1995 figures are history, not a price list, but they show how wide the spread can be. The premium appears to track quality. GIA calls colour the most important quality factor for ruby and notes that fine-quality rubies over one carat are very rare, with price rising significantly as size increases.

Pay a no-heat price only when the report says no heat. A listing title is not evidence.

What to check in an online auction listing

1. Read the treatment line on the report image. "No heat" in a title or description must be backed by the report's own wording, such as NH or "no indication of thermal treatment".
2. Verify the report number on the laboratory's website; our guide on how to verify a gemstone lab report walks through it.
3. Read every comment. A residue grade, a diffusion or glass-filling code, or any note of clarity enhancement puts the stone in a different category from an unheated or heat-only stone.
4. Note the report's date and lab. Detection keeps evolving: SSEF reported in 2018 that only some low-temperature-heated Mozambique rubies show the inclusion changes typical of heating, while others show little or none.
5. If the report does not state no heat, the useful comparison is with heated stones of similar appearance.

For bidding beyond treatments, see our checklist for buying gemstones at online auctions, and for the wider picture of treatments and report types, our guide to gemstone treatments and laboratory certification.

Where heated stones fit

A disclosed, heat-only ruby or sapphire is natural corundum with a widely used enhancement, and for a given budget it may show a stronger colour than an unheated stone. The main risks lie elsewhere: paying an unheated price for a heated stone, or mistaking glass-filled material for an ordinary ruby, which GIA says should only be cleaned with a damp cloth.

Our rubies and blue sapphires are sold at fixed prices, and every stone is listed with its laboratory, report number and treatment status; at the time of writing, all are reported as unheated. Our certification and treatments page explains the labs we use, and you can request a quotation or ask on WhatsApp from any product page.

This article discusses prices and value using published laboratory, auction-house and historical market sources. Past prices are no guide to future ones. It is general information, not investment, tax or legal advice.

Frequently asked questions

Is a heated ruby or sapphire still natural?

Yes. Heating is used to improve the colour or clarity of natural corundum. It should be disclosed, and GIA notes that rubies confirmed as unheated command a premium.

What does "no indications of heating" mean on a report?

It is the standard LMHC phrase, abbreviated NH, used when a laboratory finds no evidence of heating. GRS writes "no indication of thermal treatment"; its H(a) and H(b) codes, by contrast, mean heated with insignificant or minor residues.

Are beryllium-diffused and glass-filled stones worth as much as heated ones?

No. GIA states that diffused and glass-filled rubies are worth less than heated rubies.

How much more does an unheated ruby cost?

We found no reliable single figure. GIA confirms a rarity premium, and Richard Hughes recorded 1995 discounts of up to 40% for high-temperature-heated better Mogok rubies, but the gap appears to vary with colour, size and origin.