Quick answer
XRF analyzers deliver elemental data in seconds but read only the outermost surface, so a piece with thick genuine-metal plating over a different core can pass the scan. Electrical-conductivity testers like the Sigma Metalytics Precious Metal Verifier measure through the bulk of the piece, catching what XRF misses. Acid testing costs very little but marks the metal and reads only the surface. For large bars, ultrasonic velocity testing adds coverage no other portable method provides. No single test closes every gap: the combination is the strategy.
A single gold test can give you a false sense of security. That is not an argument against testing. It is an argument for understanding exactly what each method measures, where it stops, and what kinds of counterfeits it cannot detect. Sophisticated precious metal fakes are a documented presence in secondary markets, coin shows, and estate sales, noted in investor alerts published by FINRA and the SEC. This guide breaks down the four main testing approaches available today, compares them on the dimensions that matter to buyers and sellers, and recommends a practical setup for different user types.
Four Methods at a Glance
The table below summarizes the key trade-offs. Each method gets a full section below.
| Method | Equipment cost | Speed per piece | Destructive? | Reads surface or bulk? | Catches thick plating over a different core? | Best for |
|---|---|---|---|---|---|---|
| XRF analyzer | High (commercial investment) | 10 to 60 seconds | No | Surface only | No | Volume dealers; refinery intake; elemental breakdown |
| Electrical conductivity (e.g., Sigma Metalytics) | Mid-range | 2 to 10 seconds | No | Through the piece (bulk) | Yes | Stackers; coin shops; estate buyers; pre-sell verification |
| Acid testing | Low | 1 to 2 minutes | Yes (minor mark) | Surface only | No | Karat confirmation on jewelry; budget verification |
| Ultrasonic velocity | Mid to high | 30 to 90 seconds | No | Through the piece (full depth) | Yes | Kilo bars and larger; vault operators; institutional buyers |
XRF Analyzers: Fast, Precise, and Surface-Only
X-ray fluorescence (XRF) analysis fires a beam of X-rays at the metal surface. The atoms absorb and re-emit those X-rays at wavelengths unique to each element. The detector reads those emissions and calculates elemental composition in percentage by weight, typically in 10 to 30 seconds. For a dealer processing dozens of pieces per hour, that workflow is genuinely useful.
The limitation is physical and unavoidable. XRF interrogates only the outermost layer of the metal. How deep that layer is depends on the element being analyzed and the specific instrument’s configuration. Check the manufacturer’s published penetration depth specifications for the exact model and target elements before using any XRF result as your sole verification for a high-value piece. A piece with a sufficiently thick plating of the target metal over a different interior material will return an elemental reading consistent with the genuine article. The XRF sees gold. It cannot see what is underneath the gold.
Professional-grade XRF instruments represent a significant capital investment. Portable handheld analyzers designed for commercial jewelry and precious metals workflows are built for coin shops, jewelry counters, and refinery intake stations. Pricing varies by brand, model tier, detector configuration, and accessories; verify current figures with manufacturers or authorized distributors. For individual stackers or private buyers who handle modest volumes, the cost-per-piece economics rarely justify the equipment alone.
Used as part of a layered approach, XRF earns its place. It provides elemental precision that other portable methods cannot match, identifies mixed alloys, and screens obvious non-precious metals instantly. Used alone on a high-value piece where the counterfeit type is unknown, its surface-only limitation carries real risk.
Electrical-Conductivity Testing: Through-the-Piece Verification
Electrical-conductivity testers work on a different physical principle. Instead of interrogating the surface with X-rays, they use an electromagnetic coil to measure how electricity moves through the bulk of the piece. Because the measurement passes through most of the metal’s thickness rather than stopping at the surface, it catches a specific category of fakes that fool XRF entirely: pieces constructed with a genuine-metal exterior plating over a completely different core material.
The Sigma Metalytics Precious Metal Verifier is among the most widely used instruments in this category among independent dealers and private stackers. It identifies precious metals by comparing the measured conductivity signature against reference values for gold, silver, platinum, and palladium. Common counterfeit core materials carry electrical conductivity signatures that differ substantially from genuine precious metals. A mismatch registers as a failed test even when the surface would read correctly on XRF. Verify the current model lineup, pod options, and size ranges on the Sigma Metalytics website before purchasing, as the product specifications and compatible piece dimensions evolve over time.
The trade-off is purity granularity. Conductivity testing confirms that a piece is gold (or silver, platinum, or palladium) and is broadly consistent with the expected purity range for that metal type. It does not deliver the precise elemental breakdown that XRF provides. For buyers who need to know exact fineness, particularly for silver where the conductivity difference between .999 fine and .925 sterling is smaller, acid testing or fire assay is still required to confirm karat. For buyers who need to know whether a coin is genuine gold or a plated fake, conductivity testing is the more reliable first gate.
The non-destructive, fast nature of conductivity testing also makes it practical at the point of purchase. A buyer at a coin show or estate sale can run a conductivity check in seconds without marking or damaging the piece, which is not true of acid testing.
Acid Testing: Accessible, Destructive, and Surface-Limited
Acid testing is the oldest widely used method and the most accessible by cost. A basic starter kit includes testing acids in several concentrations (formulated to match 10K, 14K, 18K, and 24K gold, or .925 and .999 silver), a testing stone, and test needles. The process: scratch the piece against the stone to leave a small metal streak, apply the appropriate acid, and observe the color reaction. The reaction pattern indicates the metal type and approximate karat range.
Two structural limitations are worth understanding before relying on acid testing as your sole verification method. First, it reads only the surface. A gold-plated piece will return the result of the plating, not the core. Second, accurate interpretation of color reactions requires practice. The visual difference between a passing result and a borderline mismatch in a 14K versus 18K test is subtle, particularly under inconsistent lighting or when the piece surface is not freshly scratched. Dealers who use acid testing professionally develop calibrated judgment over time. A first-time buyer working from an online tutorial is operating with less reliable inputs.
The destructive element is minor but real. Acid leaves a small scratch and chemical trace on the piece. On bullion coins where condition contributes to resale value, even a small mark has a measurable cost. On jewelry destined for the refinery, it is irrelevant.
Acid testing earns a place in a layered strategy because it is cheap, portable, and adds a genuine data point. Used after conductivity testing has established that the bulk metal is consistent with the claimed type, acid testing adds karat confirmation at very low cost. Used alone on a coin or bar where the counterfeit type is unknown, it leaves the most dangerous gap open.
Ultrasonic Velocity Testing: Purpose-Built for Large Bars
Ultrasonic testing sends controlled sound pulses through a metal piece and measures how fast they travel. Different metals transmit sound at different velocities. A solid gold bar and a bar with an interior section of a substitute material produce different acoustic signatures. That physical fact is what makes ultrasonic testing valuable specifically for large bars, where the economics of sophisticated counterfeiting are most attractive and where surface-reading methods have the largest blind spots.
XRF on a 400-troy-ounce bar reads only the surface, just as it does on a coin. Conductivity testing covers more of the piece but can lose sensitivity on very thick bars where the electromagnetic field does not reach the full interior. Ultrasonic velocity testing can interrogate the full depth of a thick bar, flagging voids or internal substitutions that no surface method would detect. This is the reason major vault operators, central bank auditors, and institutional custodians use ultrasonic verification as part of large-bar authentication protocols.
The equipment ranges from basic contact thickness gauges adequate for simple hollow-versus-solid detection to professional precision instruments used in nondestructive testing (NDT) for industrial and financial applications. Calibration and proper coupling agent application affect accuracy; the learning curve is steeper than for conductivity testing. Verify current product specifications from established NDT manufacturers before purchasing. For individuals holding one-ounce or fractional coins, ultrasonic testing adds cost without proportionate benefit. For anyone holding kilo bars or larger, it belongs in the verification toolkit.
Why One Method Is Never Enough
The documented categories of counterfeit precious metals use different construction techniques to defeat different tests. A piece engineered to fool XRF via thick surface plating will not fool conductivity testing. A piece calibrated to match the correct weight and diameter, defeating a simple scale and caliper check, may still fail conductivity or acid testing. The professional response to serious verification is not “pick the best single method.” It is “layer methods until each known counterfeit construction type is covered.”
A practical framework for serious stackers covers these four bases:
- Conductivity testing as the first gate on all gold, silver, and platinum pieces.
- Acid testing to confirm purity range after conductivity has established metal type.
- Scale and caliper measurements checked against published specifications for the specific product. IRS-approved coins for self-directed precious metals IRA use must meet fineness standards defined in IRS Publication 590-A; knowing those specs gives you a cross-check that costs nothing beyond a good scale.
- Ultrasonic velocity testing for kilo bars and larger format pieces before purchase.
FINRA has published investor alerts flagging precious metals fraud as an active area of concern, including counterfeits circulating through secondary markets. The SEC’s investor education pages note that physical precious metals purchases require verification due diligence. Taking that due diligence seriously means understanding the gaps each individual test leaves open.
Choosing Your Testing Setup
The right combination depends on what you buy, how often, and the value per piece.
Individual stacker / home buyer
Conductivity + acid + scale
Core kit: Sigma Metalytics Precious Metal Verifier, a basic acid test set, a calibrated scale, and digital calipers.
Run conductivity first, acid second, weight and dimensions third. This combination covers the counterfeit types most commonly encountered in coin show and secondary market purchases.
Skip XRF unless your volume justifies the investment. Ultrasonic is not necessary until you hold kilo bars.
Active coin shop / pawn operator
XRF + conductivity + acid
Core kit: XRF for high-volume intake screening, conductivity tester for any piece that warrants a second look, acid for karat confirmation on jewelry.
XRF handles volume. Conductivity catches what XRF misses. At this volume, each tool earns its cost quickly.
Add ultrasonic if you take large bars on a regular basis.
Estate buyer / large-bar holder
Conductivity + ultrasonic + XRF
Core kit: Conductivity tester for coins and small bars, ultrasonic for kilo bars and larger, XRF for elemental breakdown when mixed alloys are suspected.
Layering all three closes the main verification gaps for estate acquisitions where provenance may be uncertain and bar sizes vary.
Consult a licensed appraiser before purchasing large quantities from unfamiliar sources.
Seller pre-verifying before an offer
Conductivity + scale + coin shop visit
Practical approach: Run a home conductivity test and weight check first. Then visit a local coin dealer or read what to expect on your first visit. Many dealers test items for free or at low cost before making an offer, and seeing their test process alongside your own gives you a comparison point.
If you plan to post your metals for competitive offers, test first so you can describe the pieces accurately to buyers.
If you are testing metals ahead of a sale, one free option is to post a sealed-offer request at /sell-gold/, where up to 15 verified buyers can submit competing offers without you committing to any of them.
Selling gold, silver, or coins? Get competitive offers before you go to a shop
Goldiew’s free sell-gold request tool lets you post once and receive sealed bids from up to 15 verified precious metals buyers. You stay in control: no obligation to accept, no pressure, and competing offers give you a real-market baseline before any transaction. Browse the marketplace to see current activity, then post your request at goldiew.com/sell-gold/.
For additional background on home testing options that cost little or nothing, see our guide on free and low-cost silver detection tests. If you have a piece with acid marks or test damage and are wondering how that affects resale value, this guide on damaged bullion covers what buyers actually pay attention to.
Frequently Asked Questions
Can XRF be fooled by a well-made counterfeit?
Yes, under specific circumstances. XRF reads only the outermost surface of the piece. A counterfeit constructed with a thick layer of genuine precious metal plating over a different interior core can return a passing XRF result if the plating is deep enough that the instrument’s X-rays do not reach the core material. The exact threshold depends on the instrument model and the elements involved; check the manufacturer’s penetration depth specifications for your specific device. Combining XRF with electrical-conductivity testing closes this gap, since conductivity measures through the bulk of the piece rather than stopping at the surface.
What metals does the Sigma Metalytics Precious Metal Verifier identify?
The Sigma Metalytics Precious Metal Verifier is designed to identify gold, silver, platinum, and palladium by measuring electrical conductivity and comparing results to known reference values for each metal. The specific metals, alloy ranges, and compatible piece sizes depend on the wand or pod accessory in use. Before purchasing, verify the current product lineup and compatibility specifications on the Sigma Metalytics manufacturer website, as model availability and specifications change over time. The verifier is non-destructive and typically returns a result in a few seconds per piece.
Is acid testing accurate enough to use by itself for resale verification?
Not as a standalone method for high-value or unfamiliar pieces. Acid testing reads only the surface of the metal, so a gold-plated counterfeit will return the result of the plating, not the core. Accurate color interpretation also requires practice and consistent lighting conditions. As a second step after conductivity testing has established that the bulk metal is genuine, acid testing adds a useful purity confirmation at very low cost. Used alone on a piece of uncertain provenance, it leaves the most common high-risk counterfeit types undetected.
Can a counterfeit coin match both the correct weight and pass XRF testing?
Yes. Counterfeits engineered to match a specific coin’s diameter, thickness, and total weight can also carry surface plating thick enough to pass XRF surface analysis. This is why weight and dimension verification, while necessary, is not sufficient on its own. Electrical-conductivity testing is specifically designed to catch this class of fake, because it measures bulk electrical properties through the piece rather than reading the surface alone. FINRA’s investor alerts on precious metals fraud note that sophisticated counterfeits can pass multiple individual tests that check only one dimension at a time.
What is a practical minimum testing kit for a home stacker?
At minimum: a calibrated jeweler’s scale (accurate to 0.01 grams), digital calipers, a basic acid test set matched to the metals you buy, and an electrical-conductivity tester. Of these, the conductivity tester provides the highest counterfeit-detection value for the cost, since it is the only tool on this list that reads through the piece rather than only the surface. A scale and calipers let you cross-check against published specifications for known coin and bar products. The acid set adds karat confirmation. Together, these four tools cover the majority of counterfeit types encountered in secondary market purchases.
Does the Sigma Metalytics work on irregular jewelry and scrap as well as coins?
The Sigma Metalytics system uses interchangeable wands and pods designed for different piece geometries, including options for rings, small coins, larger coins, and flat items. Whether a specific piece of irregular jewelry or scrap falls within the size and geometry parameters for a given wand affects test reliability. Consult the manufacturer’s current documentation for compatible piece types and size ranges before testing irregular items. Very small pieces, plated jewelry with thin precious metal layers, and pieces with irregular cross-sections may return less reliable results than standard-issue bullion coins and bars.
How do coin dealers typically test items brought in for sale?
Most coin dealers use a combination of visual inspection, scale and calipers, and at least one electronic verification method, typically XRF or conductivity testing. Many dealers will test pieces for free or at minimal cost before making a purchase offer. Seeing a dealer’s testing process alongside your own home tests provides a useful second opinion. Our guide to your first coin shop visit explains what to expect. The Goldiew coin dealer directory lists verified dealers by location if you need to find one near you.
Is ultrasonic testing necessary for one-ounce coins?
Generally no. Electrical-conductivity testing is adequate for standard one-ounce coins and most fractional sizes, because the electromagnetic field used in conductivity testing penetrates the full thickness of these relatively thin pieces. Ultrasonic testing adds value primarily on bars of one kilogram or larger, where the thickness of the piece limits how well conductivity testing interrogates the interior. If you hold mostly one-ounce coins and small bars, a conductivity tester plus acid test kit covers the relevant risks without requiring ultrasonic equipment.
Can a magnet test substitute for a conductivity tester?
A magnet test is a quick first screen, not a substitute. Gold, silver, platinum, and palladium are all non-magnetic, so a piece that attracts a strong neodymium magnet almost certainly contains ferromagnetic material and is not genuine precious metal. However, a piece that does not attract a magnet could still be a counterfeit constructed from non-magnetic base metals, many of which pass a magnet test easily. Conductivity testing measures an actual electrical property of the metal through the piece’s bulk, providing far more diagnostic information than a simple magnetic response check.
Are IRS-approved gold IRA coins harder to counterfeit than generic bullion?
IRS-approved coins for self-directed precious metals IRAs, such as American Gold Eagles and American Gold Buffalos, carry standardized specifications for weight, diameter, thickness, and fineness that are published and publicly verifiable. That standardization makes it straightforward to cross-check a piece against documented specs using a scale and calipers, which adds a low-cost verification layer. However, standardized specifications also mean counterfeiters have a precise target. The counterfeit risk is not categorically lower for IRA-eligible coins. The same layered testing approach applies. IRS Publication 590-A defines the fineness requirements for IRA-eligible precious metals; your custodian or dealer should confirm that any coin purchased for IRA use meets those standards.
Sources
- IRS Publication 590-A: Contributions to Individual Retirement Arrangements (IRAs) (fineness standards for IRA-eligible metals)
- FINRA Investor Alert: Precious Metals Fraud
- SEC Investor.gov: Precious Metals
- Sigma Metalytics, Inc. (manufacturer product specifications; verify current model details at sigmametalytics.com)
- Manufacturer documentation for handheld XRF analyzers (Olympus, Bruker, Thermo Fisher Scientific; verify current penetration depth specifications with each manufacturer)
- Published coin specifications: United States Mint official product pages for American Gold Eagle, American Gold Buffalo, and American Silver Eagle dimensional and fineness standards
Manufacturer specifications cited in this guide reflect general published product information and should be verified directly with each manufacturer before making purchasing decisions. Equipment pricing and model availability change; all figures in this guide are for orientation only and are not purchase quotes.