Module 6: Authentication: Spotting Reproductions, Alterations, and Fakes

Why This Module Matters

Module 3 introduced the discipline of handling conflicting evidence honestly. This module extends that discipline into deliberate deception — pieces made or altered specifically to misrepresent what they are. The goal isn’t paranoia about every piece that comes across the counter; it’s knowing the specific, testable methods that separate a genuine concern from an honest, explainable inconsistency.

Metal Authentication: Why Acid Testing Isn’t Enough Anymore

Acid testing has been the traditional first check for gold: a nitric-acid-based solution reacts differently depending on karat purity, giving a quick surface read. But acid testing has a specific, well-documented blind spot that matters enormously for estate and trade-in work: it only tests the surface. A gold-plated piece with even a fraction of a micron of real gold on the surface will pass an acid test perfectly, because the acid never reaches the base metal underneath — brass, tungsten, or steel cores have all been documented in counterfeit or deceptively plated pieces that pass acid testing with no issue.

XRF (X-ray fluorescence) analysis solves this specific problem: rather than a binary surface reaction, XRF reports the actual elemental composition of the metal, including trace elements, and can detect a base-metal core underneath plating up to a real but finite penetration depth (commonly cited around 30 microns). The correct protocol is specific and worth following exactly: scan multiple points on a single piece (for a ring, the band, the interior, and the setting; for a chain, two clasps and a mid-link), since a single scan point can miss a partial plating job or a soldered repair using different metal. For any higher-value piece, a density check (using precise weight and water displacement) provides an additional cross-check, since a tungsten or steel core changes a piece’s density in a way that’s detectable even when the surface composition looks correct. Visual hallmark inspection still matters as a first, fast step — but hallmarks can be absent, worn, or (rarely) deliberately falsified, so they should inform, not replace, an instrumental check for anything above a routine, low-value item.

Stone Authentication: The Diamond-Moissanite Problem

The most consequential, well-documented gap in common gemstone testing equipment is the diamond-versus-moissanite problem, and it’s worth understanding precisely because the wrong tool gives a confidently wrong answer.

• Thermal conductivity testers (the classic pocket “diamond tester”) work well for separating diamond from cubic zirconia and glass, since diamond conducts heat far better than those simulants. But thermal testers cannot reliably distinguish moissanite from diamond, because moissanite’s thermal conductivity is close enough to diamond’s that it will read as “diamond” on a thermal-only device. A thermal-only positive reading is not proof of diamond; it only proves the stone isn’t glass, CZ, or most other simulants.
• Electrical conductivity testers solve this specific problem: diamond is an electrical insulator, while moissanite is a semiconductor that readily conducts a small applied current. A moissanite will register clearly on an electrical-conductivity test even after passing a thermal test as “diamond.” The professional standard is a dual-mode tester that checks both properties, since relying on thermal conductivity alone leaves the single most common and visually convincing simulant undetected.
• Neither thermal nor electrical conductivity testing distinguishes natural from lab-grown diamonds. Both register identically as “diamond” on these tools, since the underlying carbon crystal structure is the same either way. Confirming natural versus lab-grown origin requires laboratory-level testing (spectroscopy, growth-pattern analysis) beyond what any handheld device can determine — a genuine limitation worth being upfront about rather than overstating what a handheld tester can actually prove.

The practical takeaway: a confident “it’s a diamond” reading from a single thermal-only pocket tester is not sufficient professional due diligence for a piece of real value — always confirm with electrical conductivity specifically for colorless stones with any real value at stake, and don’t claim natural-origin confidence that no handheld tool can actually support.

Common Fraud Patterns in Estate and Antique Pieces

Beyond metal and stone testing specifically, several fraud and misrepresentation patterns recur often enough to watch for deliberately:

• Stone substitution in period settings: a genuinely old, correctly-dated mounting with a stone that doesn’t match the setting’s actual construction (a prong depth or bezel width clearly cut for a different stone shape or size than what’s currently seated) suggests the original stone was removed and replaced — sometimes for legitimate reasons (Module 3’s married-jewelry concept), sometimes to pass off a lower-value replacement as the “original.”
• Falsified or “enhanced” hallmarks: a hallmark that’s unusually crisp compared to the surrounding metal’s genuine wear, a hallmark shape or spacing that doesn’t match documented historical examples for the claimed maker or period, or a hallmark stamped over solder (rather than into original, undisturbed metal) are all specific, learnable warning signs.
• Reproduction pieces sold as genuine antiques: modern manufacturing techniques (laser welding, cast uniformity, modern clasp mechanisms) presented on a piece claimed to be genuinely antique is the same conflict-of-evidence pattern from Module 3, applied here specifically to deliberate misrepresentation rather than an innocent married piece.
• Glued rather than set stones: a stone that appears prong- or bezel-set but shows adhesive residue, an unusually shallow seat, or shifts slightly under gentle pressure with a loupe in view is a specific, testable red flag — legitimate antique and fine jewelry construction sets stones mechanically, not with glue.

When Suspicion Is Confirmed: What to Actually Do

Discovering a likely fraud or misrepresentation calls for the same disciplined approach from Module 3, applied to a higher-stakes conclusion: document everything (photographs, test results, exact readings) before taking any action, communicate findings to the client factually and without accusation (since the client themselves may be an innocent party, unaware their piece isn’t what they believed), and escalate to a manager or, for anything involving a significant potential loss or a pattern of suspicious activity, follow the store’s loss-prevention and compliance protocols — a topic Module 8 covers directly. Being right about a fraud finding matters less than handling the discovery professionally, documented, and without overreach into an accusation the evidence doesn’t yet fully support.

A Worked Scenario: The Convenient Diamond Tester Result

A client brings in a ring for trade-in evaluation, and a pocket thermal tester reads “diamond” on the center stone. Rather than stopping there, the associate follows the correct protocol: “This piece is valuable enough that I want to run one more check before we finalize anything — a thermal tester alone can’t fully rule out moissanite, since the two conduct heat similarly. Let me also run the electrical conductivity test, which is the one that actually separates the two reliably.” The electrical test comes back positive for conductivity, indicating moissanite rather than diamond. This is delivered to the client factually: “The stone is testing as moissanite rather than diamond — that changes today’s trade-in evaluation, but I want to be clear this isn’t necessarily anything you did; it’s common for moissanite to have been represented as diamond somewhere earlier in this piece’s history, sometimes accidentally.” This protects the store from a costly overpayment while treating the client with respect rather than suspicion.

Practice Exercise

Practice explaining, to a colleague, why a thermal-only “diamond” reading isn’t sufficient proof of a diamond, and walk through when you’d escalate to XRF metal testing versus when a hallmark and visual inspection would be sufficient. Then practice the factual, non-accusatory language for informing a client that a stone or metal tested differently than expected.

Key Takeaways

• Acid testing only checks the metal surface and can be fooled by even minimal plating over a base-metal core; XRF analysis, scanning multiple points on a piece, provides quantitative elemental composition and can detect hidden cores that acid testing misses entirely.
• Thermal conductivity testers reliably separate diamond from cubic zirconia and glass but cannot reliably distinguish diamond from moissanite; electrical conductivity testing is the specific, necessary follow-up check for colorless stones of real value.
• Neither thermal nor electrical conductivity testing can distinguish natural from lab-grown diamonds — that requires laboratory-level testing beyond any handheld device’s capability.
• Common fraud patterns include stone substitution inconsistent with a setting’s original construction, falsified or artificially “enhanced” hallmarks, modern manufacturing techniques on claimed-antique pieces, and glued rather than mechanically-set stones.
• When suspicion is confirmed, document everything before acting, communicate findings factually and without accusation (the client may be an innocent party), and escalate through proper channels rather than overreaching into an unsupported conclusion.