Silver Testing: Acid, XRF and Specific Gravity

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Last updated: August 16, 2026 · By White Metal Resources Editorial

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Silver authentication is a small science with three working methods and a couple of quick pre-screens. Each method exposes a different property of the metal. Acid reads the chemistry of the surface. XRF reads the element mix by fluorescence. Specific gravity reads the bulk density. A fake that defeats one property often reveals itself against another, which is why serious buyers run at least two tests before writing a check on a valuable piece.

This page walks through the working procedure for each method. It covers the safety rules that matter most (nitric acid is corrosive), the density map that separates silver from base metals and fake cores, and the honest limits of every technique. The goal is a single reference for an inheritor, a scrap seller, or a bullion buyer who wants to confirm that a piece is what its stamp says it is.

The three silver tests, side by side

The three practical silver tests each measure a different physical or chemical property. No single test is conclusive on its own. Buyers who handle valuable silver run more than one to cross-check the result.

Acid testing is the cheapest and fastest. A drop of dilute nitric acid on a filed spot reacts with the alloying metal (mostly copper). The color of the reaction indicates the fineness range. The test destroys a small piece of the item, and the acid itself is corrosive and requires careful handling.

X-ray fluorescence (XRF) is the most accurate everyday method. A handheld XRF instrument fires low-energy X-rays at the surface and reads the characteristic secondary X-rays emitted by each element in the alloy. The result is a percentage breakdown of the metal composition, typically in a few seconds, without any damage to the piece.

Specific gravity is the free, non-destructive method that anyone with a scale and a glass of water can run. It weighs the piece in air, then weighs it in water, and computes the density from the difference. That density is then compared against the reference density for the claimed alloy. It works well against copper-based fakes and poorly against lead cores.

Acid test: how it works and what the colors mean

Acid testing exploits the fact that silver reacts with nitric acid to form silver nitrate, which is colorless in solution, while copper reacts to form copper nitrate, which is a strong blue-green. Any alloy of silver and copper produces a color reaction whose hue depends on how much copper is present.

The working reagent for silver alloys is a dilute nitric acid solution, sometimes called a silver test acid. Commercial silver test kits sold to jewelers and coin shops contain graduated bottles of nitric acid at different concentrations, typically labeled for silver, sterling, or coin silver. The kit is applied to a small filed spot on a hidden area of the piece, and the color is read against a printed reference card.

The color reactions on a typical silver test acid run about like this. A creamy white or milky reaction indicates fine silver at .999 or higher. A dark red or brownish-red reaction indicates .925 sterling silver. A darker red or brown-red reaction indicates .900 coin silver.

A brown reaction indicates .800 continental silver. A green or blue-green reaction indicates a copper-heavy base metal, typically nickel silver or brass. No reaction at all can indicate a plating over base metal that the file did not reach.

Interpretation depends on the specific brand of test kit, so a jeweler always reads the color against the reference card that ships with the acid, not against a general chart. The physical basis is universal: the darker the red or brown, the more copper is dissolving with the silver, which means less pure silver in the alloy. A green reaction with no red at all means essentially no silver is present.

Acid test, step by step

The procedure below is the working version used at coin shops and jewelry desks. It requires a small file, a silver test acid kit, protective gloves, eye protection, and a well-ventilated workspace. A black or dark stone tile can also be used as a scratch plate if the piece is small enough to rub on a stone.

1. Choose a hidden spot on the piece. The base of a candlestick, the inside rim of a bowl, or an inconspicuous back edge of a flatware handle are all common choices. The test damages the metal in one small location, so put it where a normal viewer will not see it.
2. File through the surface to expose fresh metal. A single medium file stroke deep enough to cut through any plating or tarnish and reach the base alloy is enough. The exposed spot should show a bright fresh metal color, not the darkened patina of the outer surface.
3. Put on nitrile or neoprene gloves and eye protection. Work over a plastic tray or a laboratory drip pan, not over a wooden bench or fabric. Nitric acid stains and burns cellulose and skin on contact.
4. Place a single drop of the appropriate test acid on the filed spot. Use the acid strength recommended by the kit for the fineness you suspect. A silver test acid is a different formulation from a gold test acid and cannot be substituted.
5. Watch the color develop for 5 to 30 seconds. The reaction is nearly instant on modern reactive alloys and slower on well-passivated surfaces. Read the color against the reference card that shipped with the kit, not against a memorized chart.
6. Neutralize the acid drop with baking soda solution or plenty of water. Rinse the piece under running water, dry with a clean cloth, and polish the filed spot with a light abrasive to blend it back into the surrounding surface. Discard used gloves and any absorbent material.

Acid testing is best treated as a screening tool. It reads only the outer millimeter of the piece where the file penetrated, so a well-plated fake with a thin silver skin can pass an acid test if the file does not cut deep enough. Pair the acid test with a specific gravity check on any high-value piece.

Nitric acid safety and OSHA exposure limits

XRF: non-destructive and accurate

X-ray fluorescence is the standard authentication method at coin shops, refiners and pawn desks that handle enough precious metals volume to justify the instrument. An XRF gun fires a low-energy X-ray beam at the surface of the piece. Each element in the alloy absorbs some of that energy and re-emits characteristic secondary X-rays at element-specific wavelengths. The instrument detects those secondary emissions and computes the percentage of each element present.

The result is a table of percentages: silver 92.4 percent, copper 7.5 percent, trace zinc 0.1 percent, for a typical sterling reading. Modern handheld XRF instruments read to a fraction of a percent on the common precious metals and detect base-metal contaminants at parts-per-thousand levels. The read time is a few seconds per spot.

XRF has three practical advantages. It is non-destructive: no filing, no acid, no mark on the piece. It is fast: dozens of pieces can be scanned in a few minutes. It is quantitative: the number is a percentage, not a color that a human has to interpret. Those three properties are why XRF is the reference method at any dealer that handles high-value silver at scale.

The one big limitation of XRF is that it reads only the surface. The X-ray beam penetrates a few tens of microns into most metals. A plated fake with a silver skin thicker than the beam penetration reads as pure silver on a single face.

A serious XRF authentication of a bar or a coin includes a scan of multiple faces, a check on the edge, and, for large pieces, a shave of the surface to expose a fresh cross-section for a second scan.

The other limitation is cost. Handheld XRF instruments from the major manufacturers (Bruker, Olympus, Thermo Fisher, SciAps) sell for roughly 20,000 to 40,000 US dollars new, with a small refurbished secondary market at lower prices. That capital cost puts XRF out of reach for the individual scrap seller and into the hands of dealers who process enough volume to justify the machine.

XRF, step by step

Most sellers meet XRF at a dealer counter rather than in their own workshop. The procedure below describes what a dealer's XRF check looks like, so the seller can watch the process and confirm the reading is honest. It also describes the sequence a shop follows on its own inventory.

1. Clean the surface of the piece. Wipe off tarnish, polish residue, dust or oil with a soft cloth. Surface contamination biases the reading toward the contaminant.
2. Position the piece flat against the XRF instrument's read window. The instrument requires flush contact between the sample surface and the beam window to get an accurate percentage reading. Curved surfaces read poorly, so a round bar or a coin is placed on the flattest face available.
3. Trigger the read cycle and hold for the manufacturer's specified time. Most modern handheld XRF instruments run a 5 to 15 second read cycle. The instrument displays a progress bar and beeps when the read is done.
4. Read the elemental composition table on the instrument screen. The output lists each detected element with its measured percentage. For a genuine sterling silver piece, the reading shows silver at 92.0 to 93.0 percent, copper at 6.5 to 8.0 percent, trace amounts of other alloying metals, and no unexpected base metals like nickel or lead.
5. Scan a second spot on a different face of the piece. Any single reading confirms the surface, not the interior. A second reading on the edge, the base, or a shaved area catches a plated fake where one face passes and another face reads as base metal.
6. Compare the reading against the stamped fineness. A stamped 925 piece should read within about 1 percentage point of 92.5 percent silver on a clean scan. A meaningful gap between the stamp and the reading is a red flag that calls for a second method, either a shave-and-rescan or a specific gravity check.

Any dealer who refuses to let a seller watch the XRF read and see the numbers on the screen is a dealer to walk away from. The reading is quantitative and public, and a legitimate operation has no reason to hide it.

Specific gravity: free, non-destructive, and public math

Specific gravity, or density, is the ratio of a substance's mass to the mass of an equal volume of water at a reference temperature. The method has been used to authenticate precious metals since Archimedes computed the gold content of a crown in the third century BC by comparing its weight in air to its weight submerged in water. The math has not changed. The instruments have.

The working formula for a specific gravity check on a solid piece is: specific gravity equals weight in air divided by (weight in air minus weight in water). The result is dimensionless. It is called specific gravity when compared against water, and density (in grams per cubic centimeter) when read as an absolute number. For most practical purposes on a piece tested in water at room temperature, the two numbers are within a fraction of a percent of each other.

Pure silver has a density of 10.503 grams per cubic centimeter at 20 degrees Celsius (68 degrees Fahrenheit), per the Wikipedia summary of the silver element page. Sterling silver, at 92.5 percent silver and 7.5 percent copper, computes to about 10.36 grams per cubic centimeter using the two-component mixing rule. Coin silver, at 90 percent silver and 10 percent copper, computes to about 10.34 grams per cubic centimeter.

Those numbers are the reference. A piece that reads 10.30 to 10.40 on a specific gravity check is consistent with sterling silver. A piece that reads well below 10 is not sterling: it is copper, brass, nickel silver, pewter or another base alloy. A piece that reads above 11 has a heavy metal core, either lead or tungsten, hiding under a silver surface.

Specific gravity, step by step

The procedure below runs a specific gravity check with common household or shop equipment. Required tools: a digital scale that reads to 0.01 gram, a container of water, a length of thin thread, and a support that holds the scale above the water. The piece must hang submerged without touching the container walls or bottom.

1. Weigh the piece dry, in air. Zero the scale with any hanging apparatus already in place. Place the piece on the scale and record the weight in grams to two decimal places. This is the weight in air, called W-air.
2. Suspend the piece from the scale with a thin thread. Tie a slipknot around the piece, hang the loose end from a bar or hook above the scale platform, and let the piece hang free. Rezero the scale so the thread and hanging apparatus read zero with the piece off.
3. Fill a glass or beaker with room-temperature water and place it under the piece. The container sits on a separate stand, not on the scale. The piece dangles from the scale above, then lowers until it is fully submerged without touching the container walls or bottom.
4. Read the weight of the submerged piece. The scale now reads a lower number because the buoyant force of the displaced water pushes up on the piece. Record this reading in grams as the weight in water, called W-water.
5. Compute specific gravity. Specific gravity equals W-air divided by (W-air minus W-water). For a 100 gram sterling piece that reads 90.35 grams submerged, the calculation is 100 divided by (100 minus 90.35) equals 100 divided by 9.65 equals 10.36.
6. Compare the result against the reference table. Sterling silver reads 10.30 to 10.40. Coin silver reads 10.28 to 10.38. Fine .999 silver reads 10.48 to 10.52. Copper reads about 8.94. Lead reads about 11.35. Tungsten reads about 19.25. Nickel and brass read in the 8.4 to 8.9 range.

Precision matters. A scale that reads to 0.1 gram is not accurate enough for a specific gravity check on a small piece. A 10 gram silver coin weighed on a 0.1 gram scale carries an error of about plus or minus 5 percent in the density result, which is enough to blur the difference between sterling silver and pewter. For pieces under 50 grams, use a scale that reads to 0.01 gram or better.

Density map: silver against base metals and fake cores

The chart below plots the density of pure silver alongside sterling silver, coin silver, and the most common metals that show up as base-metal substitutes or fake cores. It is the visual reference for interpreting a specific gravity reading.

The chart makes three points obvious. First, copper, nickel and brass all sit well below silver in density, so a base-metal fake reads unmistakably lower on a specific gravity check. Second, tungsten is far denser than silver, so a tungsten-cored fake fails a density check hard rather than passing.

Third, lead sits close to silver at 11.348 grams per cubic centimeter, which is the one case where density alone cannot rule out a fake. A lead-cored piece with a silver plating can read plausibly close to sterling on a density check. It requires a second method (XRF or a shave-and-rescan) to catch.

A worked density calculation on a 100 gram sterling piece

The example below runs a full specific gravity check on a 100 gram piece claimed to be sterling silver. The number is chosen because it is large enough to make the arithmetic obvious and small enough to be a common household item like a candlestick base or a small teapot lid.

The lesson from this example generalizes to any density check. The pass zone for sterling is narrow (about 10.30 to 10.40), and the common fakes sit outside that zone in one direction or the other. The one dangerous case is lead, which sits close enough to require a second test.

Fake cores: lead, tungsten and plating

Modern silver counterfeits fall into three families, each of which defeats one or two of the three tests. Understanding the family that a suspected fake belongs to determines which test to run next.

A plated fake is the simplest and most common. A base-metal core (usually copper, brass or nickel silver) is electroplated with a thin silver skin, then stamped with a fake hallmark. It passes a quick visual inspection and can pass an XRF read on the plated face if the plating is thick enough. It fails an acid test if the file cuts through the plating. It fails a specific gravity check because the base-metal core reads far below silver.

A lead-cored fake substitutes lead for the interior of a bar or coin and covers it with a silver skin. Lead is close enough to silver in density that a specific gravity check reads plausibly (11.35 for lead against 10.50 for pure silver, or 10.36 for sterling). The lead core also gives the piece a convincing heft.

A lead-cored fake fails an XRF check if the beam catches the edge, and it fails an acid test if the file goes deep enough to reach the lead layer. Ping-testing (rapping the piece with a hard object) sometimes catches lead because the dull thud of lead is different from the ring of silver.

A tungsten-cored fake is more sophisticated and more common in fake gold bars than in fake silver bars, because tungsten (19.254 grams per cubic centimeter) matches gold (19.32) almost exactly and matches silver (10.50) not at all. A tungsten-cored silver fake reads about 19 on a specific gravity check, which is a hard fail. Tungsten shows up in silver only in poorly executed counterfeits that reuse a gold-fake mold.

The counterfeiter's dilemma is that no single fake material matches silver in density, chemistry and XRF signature all at once. Copper is right on chemistry but wrong on density. Lead is close on density but wrong on chemistry and XRF. Tungsten is wrong on density and chemistry both. That is why the three-test approach works. A fake designed to defeat one test almost always reveals itself against another.

Method comparison table

The table below rolls up the three silver testing methods on the axes that matter most to a seller or a buyer: cost, accuracy, destructive or not, and which fakes each method catches or misses. It is the working reference for choosing which test to run first on a given piece.

Cost and accuracy ranges reflect current handheld XRF pricing from the major manufacturers and typical silver acid test kit pricing at jewelry-supply retailers. Density references are element densities from the Wikipedia element pages and computed alloy densities from the two-component mixing rule. Checked August 2026.

The practical order of operations is: magnet test first (free, one second), then specific gravity (free, five minutes), then acid or XRF depending on which is available and how valuable the piece is. A serious buyer of a bullion bar runs XRF plus a shave-and-rescan. A household inheritor sorting flatware runs the magnet-and-density pair on every piece.

Honest limits of each method

Every test on this page has failure modes. Understanding those failure modes prevents false confidence on a suspicious piece and prevents false alarms on a legitimate one.

The acid test has three failure modes. It destroys the tested spot, so it is not suitable for collectible or antique pieces where surface integrity matters. It reads only the outer layer, so a thick silver plating can pass. And the color reading is subjective enough that a beginner sometimes misreads the reference card, especially between sterling and coin silver where the colors are similar shades of red.

XRF has two failure modes. It reads the surface only, so a plated fake can defeat it if only one face is scanned. And the instrument cost puts it out of reach for individual sellers, who have to rely on a dealer's honesty about the reading rather than seeing the instrument themselves. The mitigation is to watch the screen during the scan and ask to scan a second face.

Specific gravity has three failure modes. It is sensitive to hollow interiors, attached non-silver parts (steel blades, wooden handles) and scale precision. A hollow silver piece reads a lower density than the solid alloy because the trapped air displaces additional water. A piece with any attached base metal distorts the reading toward the base metal. And a scale that reads only to 0.1 gram carries too much error to distinguish silver from other reasonably dense metals on small pieces.

Beyond the individual methods, three general limits apply. First, no test on this page appraises a piece for antique or collector value. A signed Georg Jensen coffeepot is worth multiples of its melt value to a specialist dealer, and a scrap desk pays only the metal content.

Second, US pre-1965 coinage has a numismatic authentication protocol (weight, diameter, edge reeding, magnification of the design) that is separate from metal composition. Third, this page is educational. It is not a substitute for a formal appraisal by a certified appraiser or a laboratory assay by an accredited assay office.

The Federal Trade Commission publishes consumer guidance on bullion and coin transactions that reinforces the same principle. Verify metal content before paying, and get the pricing mechanics in writing before the piece changes hands.

Silver testing questions, answered

How do I test silver at home without acid?

Run a magnet test first (a strong neodymium magnet should show no attraction to real silver). Then run a specific gravity check: weigh the piece in air, weigh it hanging in water, and compute density as weight in air divided by (weight in air minus weight in water). Sterling silver reads about 10.36 grams per cubic centimeter. Any reading well below 10 rules out silver. Any reading well above 11 indicates a lead or tungsten core.

What color does silver turn with nitric acid?

A drop of dilute nitric acid on a filed silver alloy spot produces a color reaction whose hue depends on the copper content. Fine .999 silver gives a creamy white reaction. Sterling .925 silver gives dark red. Coin .900 silver gives brown-red. Continental .800 silver gives brown. Copper-heavy base metals like nickel silver or brass give green or blue-green. Read against the reference card shipped with the test kit.

Is XRF testing accurate for silver?

Yes for the surface composition. A calibrated handheld XRF instrument reads silver content to about a fraction of a percent, along with the percentages of copper and any other alloying metals. The catch: XRF reads only the outer few tens of microns of the piece. A plated fake with a thick silver skin can read as pure silver on a single-face scan. Rigorous XRF authentication scans multiple faces, plus a surface shave for high-value pieces.

Can specific gravity detect a fake silver coin?

Usually yes for copper-cored, brass-cored, nickel-cored or tungsten-cored fakes, all of which read densities far from silver's reference of 10.50 grams per cubic centimeter. The one case where specific gravity alone is not enough is a lead-cored fake, because lead reads 11.35 which is close enough to sterling (10.36) to require a second method to distinguish. For coins specifically, weight and diameter tolerances published for the coin series add another check that catches most physically imitated fakes.

Which silver test is the most reliable?

XRF is the single most reliable everyday test for stamped fineness, but only for surface composition. Fire assay (destructive melting of a chip to weigh the recovered silver bead) is the reference laboratory method that settles disputes. In practice, most authentication questions are settled by combining two methods: magnet plus specific gravity for a fast home check, or XRF plus specific gravity for a dealer counter check.

Do I need a jeweler to test silver?

No for a first-pass check. A magnet test, a specific gravity check with a household scale, and a visual hallmark inspection can be done at home. A jeweler or coin shop with an XRF instrument is needed only when a stamp is missing, a specific gravity reading is ambiguous, or a piece is valuable enough to justify professional verification. Antique appraisers and formal laboratory assays are separate services for higher-value items.

What is the ice test for silver and does it work?

The ice test places an ice cube on a piece and watches how quickly it melts. Silver has one of the highest thermal conductivities of any common metal, so ice on real silver melts noticeably faster than ice on a base-metal piece of similar thickness. The test is qualitative and works best as a side-by-side comparison. Copper conducts heat too, so a copper fake can pass. Use it as a sanity check, not a primary test.

How accurate does my scale need to be for a specific gravity check?

For a piece under 100 grams, use a scale that reads to 0.01 gram. On pieces under 20 grams, a scale that reads to 0.001 gram is preferable. A kitchen scale reading only to 1 gram carries about 5 percent error on a 20 gram sample. That blurs the difference between sterling silver and pewter. Digital jewelry scales that read to 0.01 gram are widely available at low cost.

Sources

1. Silver, element data (density 10.49 to 10.503 grams per cubic centimeter at 20 degrees Celsius, atomic number 47, chemistry and reactivity notes). Checked August 2026.
2. Sterling silver composition: 92.5 percent silver and 7.5 percent copper by weight, minimum millesimal fineness 925. Checked August 2026.
3. Copper, element data (density 8.935 grams per cubic centimeter at 20 degrees Celsius, chemistry of copper-nitrate reactions). Checked August 2026.
4. Lead, element data (density 11.348 grams per cubic centimeter at 20 degrees Celsius). Checked August 2026.
5. Tungsten, element data (density 19.254 grams per cubic centimeter at 20 degrees Celsius). Checked August 2026.
6. Nickel, element data (density 8.907 grams per cubic centimeter at 20 degrees Celsius). Checked August 2026.
7. Nitric acid, chemistry and hazard summary (reactions with silver and copper, corrosive properties). Checked August 2026.
8. OSHA Table Z-1, Permissible Exposure Limits for Air Contaminants (nitric acid CAS 7697-37-2, 2 parts per million 8-hour TWA, 4 parts per million ceiling). Checked August 2026.
9. X-ray fluorescence, principle of operation (characteristic secondary X-rays for elemental composition analysis). Checked August 2026.
10. Specific gravity, working formula and Archimedes-based measurement (weight in air divided by weight of displaced water). Checked August 2026.
11. Federal Trade Commission, Consumer Advice: Investing in Bullion and Bullion Coins (verify fineness, get pricing in writing). Checked August 2026.
12. FINRA, Investment Fraud: Precious Metals (retail investor guidance on precious metals verification and transactions). Checked August 2026.
13. London Bullion Market Association, Good Delivery specification for accredited silver bars and refiners (fineness and assay standards). Checked August 2026.