Do Lab Grown Diamonds Pass a Diamond Tester?

A thermal tester assesses how readily heat moves through the material being tested. For example, Presidium describes its Diamond Mate instrument as testing diamonds through their thermal properties. Presidium’s Diamond Mate specifications.

Laboratory-grown diamonds have diamond’s carbon crystal structure and nearly the same chemical, optical and physical properties as natural diamonds. Their laboratory origin does not make them a different gemstone material. GIA’s explanation of laboratory-grown diamonds.

A conductivity reading nevertheless has a limited purpose. It does not measure the diamond’s age or establish the environment in which its crystal grew.

For the wider material explanation, read our guide to whether lab grown diamonds are real.

These distinctions are supported by Presidium’s combined-tester specifications, GIA’s screening-device explanation and GIA’s research on laboratory identification.

The size or appearance of a device does not tell you its capabilities. Ask for the make, model and purpose of the instrument before interpreting the result.

Moissanite can give a diamond-like response on a thermal tester because it also conducts heat well. Although its composition differs from diamond, this particular property makes heat-only testing insufficient for conclusively identifying the material. GIA’s explanation of moissanite’s thermal properties.

Combined testers add electrical measurements to help distinguish the materials. Presidium’s Multi Tester III, for example, uses both thermal and electrical properties when testing colourless diamonds and moissanites. Presidium’s Multi Tester III specifications.

A seller demonstrating a thermal “diamond” reading has therefore shown the response to that test. Ask what additional assessment supports the gemstone’s identification.

Our lab grown diamonds versus moissanite guide explains the wider differences between these materials.

Electrical behaviour introduces another complication. Some diamonds conduct electricity sufficiently to produce a moissanite reading on testers that use electrical conductivity. GCAL specifically identifies this as a possible result for laboratory-grown diamonds and certain natural blue diamonds. GCAL’s guidance on unexpected tester readings.

An unexpected result therefore needs investigation. It should not automatically be treated as proof that the stone is moissanite, or dismissed solely because the seller describes it as diamond.

Record the instrument model and the exact result. Ask whether the equipment is suitable for that stone and whether the test followed its instructions. If the result remains unresolved, arrange examination using additional methods appropriate to gemstone identification.

A growth-method label alone does not resolve the discrepancy. Information about CVD or HPHT should be considered alongside the actual stone and its documentation.

On an instrument designed to screen for natural diamonds, “Pass” can have a different meaning from a diamond indication on a thermal tester.

GIA explains that its iD100 uses spectroscopic technology and reports “Pass” for natural diamonds and “Refer” for stones requiring further testing. Interpret those results within the device’s stated scope and operating instructions. GIA’s iD100 guidance.

A referral is not a completed identification. It should not be presented as a definite finding that the stone is laboratory-grown, moissanite or another material.

For example, a stone could give a diamond-like thermal response and then receive a referral from an origin screener. Those results address different questions. Further examination resolves what the screening result leaves open.

This is why a shop demonstration should include an explanation of the instrument’s purpose, not simply the word shown on its display.

Start with the equipment’s intended use. Check the permitted gemstone types, colour range, minimum size and mounting conditions. Follow the manufacturer’s instructions for power, readiness, operating temperature and probe placement.

For mounted jewellery, contact with the metal setting also matters. Presidium explains that certain testers produce an intermittent metal-alert sound when the probe touches metal. That signal should be interpreted according to the instrument’s instructions. Presidium’s tester troubleshooting guidance.

The way a loose stone is supported can also be part of the specified testing procedure. Presidium’s guidance shows that incorrect handling during electrical testing can affect the result. Presidium’s explanation of testing conditions.

Repeating a test under the same unsuitable conditions does not resolve the underlying problem. Have the operator check the procedure and the instrument’s suitability before drawing a conclusion.

When jewellery contains several stones, identify which stone each result concerns. Testing the centre stone does not establish the identity of every surrounding stone.

Gemological laboratories examine diagnostic characteristics associated with diamond growth and use analytical equipment to investigate them. GIA’s research describes the role of advanced testing in distinguishing laboratory-grown diamonds from natural diamonds. GIA’s research on diamond identification.

This is a different task from checking whether a stone transfers heat like diamond.

If origin is the unresolved question, ask for an assessment specifically capable of addressing it. A further thermal test alone cannot supply the missing growth-origin information.

For an existing purchase, keep the original product description, invoice, laboratory document and details of the unexpected result together. Providing that information helps the examiner understand the question that needs to be resolved.

A laboratory report provides recorded findings about the stone examined. IGI describes its laboratory-grown reports as documenting characteristics and identifying laboratory-grown origin. IGI’s laboratory-grown diamond report guidance.

Check the document through the issuing laboratory’s verification service and arrange for the physical stone to be compared with its recorded details. Relevant information may include measurements, identifying characteristics and an inscription where present.

The connection between the document and the stone matters. A report supplied with a purchase should not simply be assumed to describe whichever stone has just been tested.

Read the actual document’s origin statement, service description and comments. Our IGI versus GIA documentation guide explains why different report formats should be compared carefully.

If the paperwork and testing appear inconsistent, ask for a clear explanation supported by appropriate examination. Keep the question open until the discrepancy has been resolved.

To discuss a laboratory-grown diamond requirement, contact Uniglo Diamonds with your preferred shape, size, budget and documentation requirements.

Ask to review the individual stone’s specifications and laboratory document. If a testing demonstration forms part of the discussion, request the instrument’s name and an explanation of what its result establishes.