"No indications of heating" means the lab found no evidence that a ruby or sapphire was heat treated. Its code is NTE. The phrase reports what the lab observed, which is why careful reports do not simply say "unheated".
The codes on this page come from the Laboratory Manual Harmonisation Committee, or LMHC, a group of gem labs that agreed shared report wording. Its sheets name CISGEM, GAAJ-Zenhokyo, GIA, GIT, Gübelin and SSEF.
TL;DR
NTE stands for no indications of heating. TE stands for indications of heating.
TE1 to TE5 add how much residue from the heating process sits in healed fissures.
The wording describes a finding about a stone, and it is not a guarantee of its whole history.
Sellers often shorten it to "no heat" or "unheated". Read the report itself.
The Heating Codes on a Report
Code | What the report is saying |
|---|---|
NTE | No indications of heating |
TE | Indications of heating, no residue noted |
TE1, TE2 | Heating, with minor residue in healed fissures |
TE3, TE4 | Heating, with moderate residue in healed fissures |
TE5 | Heating, with significant residue in healed fissures |
C1, C2, C3 | Minor, moderate or significant residue in cavities |
This is our short summary. The full wording is in the LMHC sheets linked below, which are dated 2010 and 2011, so a report's own key takes priority. A lab outside the committee may use different terms.
Does No Indications of Heating Mean Unheated?
Not as a promise. The phrase says the examination showed no signs of heating. It does not claim to know everything that happened to the stone before it reached the lab, which is why we repeat the wording on reports rather than write "unheated".
Detection can also be subtle. The LMHC notes that certain heating conditions can leave some internal features unchanged while altering others. When a lab sees that pattern, the comment becomes "indications of (low temperature) heating".
Why the Wording Matters for Price
Heating is a large part of how a ruby or sapphire is priced, so these few words carry real money. We show what that gap looked like in named sales in Heated vs. Unheated Sapphire and Same Sale, 5.7x Apart.
How to Check the Claim
Ask for the report. A listing that says "no heat" is the seller's wording.
Read the comment line. Look for the exact phrase or code, and any residue code beside it.
Check the report with the lab. Match the number, the weight and the dimensions to the stone. Gübelin says its online data is informative and non-binding, and that the original report is the valid document, so treat a match as a first check.
FAQ
What does NTE mean on a gem report? No indications of heating, in the LMHC's shared wording for corundum, which covers ruby and sapphire.
What is the difference between NTE and TE? NTE means the lab found no signs of heating. TE means it found signs of heating done to change color or transparency.
Is TE1 worse than TE? TE1 tells you residue from the heating process was found in healed fissures, in a minor amount. Plain TE notes no residue. Neither code alone sets a price.
Does it apply to emerald? No. Emerald reports use a separate scale, explained in Minor Oil Emerald.
Useful Sources
Carat Brief is editorial and is not investment advice. Get sourced gem prices, free, every Tuesday.