Thermal Tester is a device that:

• A. Measures density
• B. Measures thermal conductivity to help separate natural and lab-grown diamonds from most simulants
• C. Tests only hardness
• D. Measures color

Answer: (B)

The test centers on using heat flow as a identifying fingerprint. A thermal tester measures how quickly heat moves through the stone when a small heat pulse is applied. Diamonds conduct heat extremely well compared with many common diamond simulants, so the device signals a rapid heat transfer that helps distinguish true diamonds (natural or lab-grown) from most simulants such as cubic zirconia or glass. This makes it a practical tool for separating natural and lab-grown diamonds from those other materials. Keep in mind that some substances with high conductivity, like certain diamond-family simulants, may blur the line, so testers are most reliable when used alongside other identification methods.