Protected: Precious Metals Career Accelerator

Basic Testing Methods

Valuation and Authentication

When someone walks in off the street with gold or silver to sell, your job is to determine as quickly and accurately as possible whether the material is what it claims to be. No single test tells the whole story. Professionals use a combination of methods, layering observations on top of each other until they have enough confidence to make a decision. This lesson covers the hands-on methods used at the counter every day. More advanced electronic testing with Sigma and XRF devices is covered in the next lesson.

Safety Note

The acid test involves corrosive chemicals including nitric acid. Always work in a ventilated area, wear gloves and eye protection, and follow proper handling and disposal procedures for any acids used in your shop.

Step One: Read the Hallmarks First

Before reaching for any testing equipment, examine the piece closely for hallmarks. Hallmarks are stamps indicating metal content and can save you significant time. More importantly, certain hallmarks tell you immediately that the item is not solid gold, meaning there is no point running a gold test on it.

The following marks indicate the item is NOT solid gold:

Gold Filled. A layer of karat gold mechanically bonded to a base metal core. Common in vintage American jewelry.

Gold Plated. A thin electroplated layer of gold over base metal.

Gold Electroplated.

GEP

Gold Electroplate.

RGP

Rolled Gold Plate.

HGE

Heavy Gold Electroplate.

1/20 14K GF

Fraction stamps indicate the gold layer makes up that fraction of total weight. Still not solid gold regardless of the fraction.

GOLD TONE / GOLD COLOR

Decorative finish only. No gold content.

GOLD WASH

Extremely thin gold coating over base metal.

VERMEIL

Gold plated sterling silver. The silver may have value but the item is not gold.

PLAQUÉ OR

French equivalent of gold plated. Seen on European pieces.

Marks that indicate solid gold content:

Karat stamps: 10K, 14K, 18K, 22K, 24K

European decimal equivalents: 375, 417, 585, 750, 916, 999

The absence of any hallmark does not mean an item is not gold. Older pieces and some international items are often unstamped. It simply means you need to test.

Step Two: Visual Inspection

Before any chemical or physical test, look at the piece carefully.

Color

Genuine gold has a warm, consistent yellow tone in 14K and 18K, and a deeper richer yellow in 22K and 24K. Discoloration, green tinting on the skin from wearing, or green and dark patches on the piece itself suggest base metal beneath a plated surface.

Wear Points

On rings, bracelets, and clasps, the high contact areas such as edges, prong tips, and the inside of ring shanks wear first. If the color at a wear point differs from the rest of the piece, you may be looking at plating wearing through to a different metal beneath.

Weight and Feel

Gold is dense. A piece that feels surprisingly light for its size warrants extra scrutiny. For coins, weight is particularly useful since published specifications are easy to find. A genuine 1 oz American Gold Eagle weighs exactly 33.931 grams. For bars, manufacturers publish specifications as well. For random jewelry such as a used bracelet, you cannot look up expected weight, but experience handling gold daily will develop your intuition quickly.

Step Three: The Magnet Test

The magnet test is one of the fastest first screens available and costs almost nothing. Use a strong rare earth magnet. Standard household magnets are not powerful enough to perform this test reliably. When purchasing one, search Amazon or similar retailers for a “super magnet” to find the appropriate strength.

Pure gold is not magnetic. Silver, platinum, and palladium are also not magnetic. If a piece is strongly attracted to the magnet, it almost certainly contains significant ferrous or strongly magnetic material and is not what it claims to be.

Important Limitation

Passing the magnet test does not mean a piece is genuine. Many base metals used in fakes, including copper, brass, zinc, and aluminum, are also not magnetic and will pass this test easily. The magnet test eliminates obvious fakes but cannot confirm authenticity on its own.

Nuances every professional should know:

Diamagnetism in Fine Gold and Silver

A high purity gold bar (.999 fine or 24K) will exhibit a subtle pushing or sliding effect when a strong magnet is passed over it. This is called diamagnetism. Gold at high purity very slightly repels magnetic fields, causing a super magnet to slide more slowly across the surface than expected. Silver also exhibits this property. It is not dramatic, but with practice it becomes a recognizable characteristic of genuine high purity metal.

Magnetic Clasps

Jewelry clasps are almost always made with a stainless steel spring mechanism, which is magnetic. Do not mistake a magnetic clasp for evidence that the rest of the piece is not gold. Always test the body of the piece away from the clasp.

Legitimate Magnetic Alloys

Some genuine gold alloys are slightly magnetic due to their metal composition. EternaGold, a proprietary alloy sold through QVC, is a known example of a genuine gold product that tests slightly magnetic. If a piece is slightly magnetic but passes other tests and looks and behaves like gold, magnetism alone should not cause you to reject it. Context matters.

Step Four: The Ping Test for Coins

Genuine silver and gold coins produce a distinct clear ringing tone when struck or dropped onto a hard surface. Base metal coins, plated coins, or filled coins produce a dull thud or a noticeably different tone.

To perform the test, balance a coin on your fingertip and tap the edge lightly with another coin or a pen. A genuine silver coin such as a Morgan Dollar or American Silver Eagle will ring with a clear, sustained, bell-like tone that lingers for a moment. A fake or base metal coin will produce a flat, dead sound with little sustain.

Smartphone apps are available that listen to a coin’s ring and compare it against a database of known genuine coins, returning a pass or fail result. These apps have become a practical tool in modern coin dealing and are worth adding to your counter workflow.

The ping test works best on coins and some bars, but it is not normally useful for jewelry.

Step Five: The Acid Test

The acid test is the most widely used chemical screening method at the counter. It is fast, inexpensive, and accessible. However, it is important to understand exactly what it does and does not tell you.

What the Acid Test Does

A drop of acid is applied to an exposed sample of the metal. The acid reacts differently depending on the metal’s composition. For gold testing, nitric acid is the primary reagent, with different acid strengths used to differentiate between karat levels. A positive result means the metal at the point of contact resisted the acid in a manner consistent with gold at a certain karat.

The Scratch is Critical

The acid only tests as deep as the metal is exposed. If you simply drop acid onto a polished surface, you are only testing the outermost layer. A gold-plated item can easily fool a surface-only acid test. For this reason professionals use one of two approaches. The first is to rub the item firmly on a testing stone, transferring a streak of metal from the item onto the stone, then applying acid to that streak. The second, more penetrating method is to use a metal file to scratch into the body of the piece itself, then apply the acid drop directly into the filed groove. The file method reaches below any plating and gives a more reliable result on suspicious pieces. For extremely thick pieces of jewelry, it is not unheard of for a dealer to use a drill to penetrate deep into the metal.

Not a Precise Tool

The acid test can tell you approximately whether a piece is gold and roughly what karat range it falls in, but it is not an exact analytical tool. It is a screening method, not a certification.

Passing the Acid Test is Not Enough

Just because a piece does not dissolve or discolor under acid does not mean it is gold. A professional verifies multiple characteristics together:

•Genuine gold rubbed on a testing stone leaves a yellow streak.

•Genuine gold has appropriate malleability and feel.

•Genuine gold looks like gold throughout, including at wear points and filed areas.

•Genuine gold has appropriate weight and density.

A piece that passes the acid test but fails on color, weight, streak, or behavior should still be treated with suspicion. The acid test is one data point, not a verdict.

Specific Gravity

Specific gravity testing determines the density of a metal by measuring its weight in air versus its weight submerged in water. It is a valid authentication option for pure or near-pure metals such as .999 fine gold and silver bars, where the expected density is a known fixed value and a direct comparison can be made.

For alloys, the result is less definitive. Different alloy combinations at the same karat can produce varying densities, making a clean comparison more difficult. Specific gravity is rarely used in modern client-facing counter transactions due to the setup required and the availability of faster electronic tools, but it remains a legitimate authentication option in the right context. Sigma and XRF devices have largely replaced it for everyday counter use. Specific gravity is an excellent option to test pure gold and silver bars that are getting a false negative result on a Sigma.

Layering Your Tests

No single test is definitive. A professional uses visual inspection, hallmark reading, the magnet, the acid, and judgment developed from handling genuine material every day. When multiple tests point in the same direction and the piece looks, feels, and behaves like what it claims to be, confidence increases. When any test raises a flag, slow down and investigate further. The next lesson on Sigma and XRF testing covers the electronic tools that provide the most reliable non-destructive analysis available at the counter today.