Gem Instruments Hot Point Model No. 508 (c. 1960s)

This artifact is a vintage Gem Instruments Hot Point, Model No. 508, a specialized gemological instrument historically used for destructive gemstone testing and material identification. Designed for professional gemological laboratories, the hot point was primarily employed when conventional non-destructive testing methods proved inconclusive.

A major review published in the Fall 2003 issue states the between 1958 and 1960, Crowningshield investigated numerous gemstone treatments and imitations, including "the 'sweating' reaction of wax-treated turquoise to a hot point".  The article further explains that this observation originally appeared in a 1959 "Highlights at the Gem Trade Lab in New York" entry, which is the earliest documented Gems & Gemology-related reference for the usage of hot point in gemology.

The instrument features a wooden-cased control box equipped with an adjustable temperature dial, allowing the operator to regulate the heat supplied to the probe.

Heating Probe

A pen-style handheld probe fitted with a fine metal tip serves as the testing element. Under operation, the tip can be heated to a dull red glow for controlled point-contact testing.

Hot point testing became especially relevant during the mid-1900s as synthetic plastics and imitation gem materials became increasingly common in the jewelry trade. Materials such as Bakelite, celluloid, Lucite, and various resin compounds could visually imitate amber, coral, ivory, jet, and even some gemstones. Traditional visual inspection alone was often insufficient for reliable identification.

The hot point offered a direct method of separating natural materials from synthetic imitations by observing:

• Surface reaction to heat
• Melting behavior
• Odor released during testing
• Presence of fillers or coating

Plastic and Wax Identification

The instrument was commonly used to distinguish plastic imitations and wax-coated materials from natural gemstones or organic substances. When the heated probe contacts plastic, the surface will soften or melt and may emit a distinctive chemical odor.

Organic Material Examination

Gemologists also utilized the hot point to identify organic gem materials such as coral, amber, and similar substances. Genuine organic materials often produce characteristic odors when briefly exposed to the heated tip. For example, natural coral may release an odor resembling burnt hair.

Detection of Fillers and Treatments

The hot point could assist in detecting fracture fillings or surface treatments involving glass, resin, wax, or oils. These substances may react visibly or produce odor when exposed to concentrated heat at the point of contact.

This instrument is preserved as part of a museum archive and research collection. No units are currently available for sale.