What Is an Assay and How Refiners Work

What an assay actually measures

An assay is a quantitative chemical test. For gold, it tells you the fineness of a sample expressed either as a decimal (0.9999), as parts per thousand (999.9), or as karats (24K). A jewelry stamp such as “18K” or “750” is a manufacturer claim. An assay is an independent measurement of that claim.

The distinction matters when money is on the table. A ring stamped “14K” is nominally 585 parts per thousand pure gold. If the actual assay comes back at 578, the stamp is within normal tolerance. If it comes back at 520, the piece is under-karated and worth roughly 11 percent less than the stamp implies. Reputable refiners assay every lot because they cannot pay you accurately without knowing what the metal really contains.

Three assay methods dominate the precious metals industry: fire assay, X-ray fluorescence (XRF), and inductively coupled plasma (ICP) spectroscopy. Each has a different purpose, cost, and level of precision.

Fire assay: the reference method

Fire assay is the oldest gold testing method still in use and remains the international reference standard for determining gold content. The technique, sometimes called cupellation, dates to antiquity but is now codified as an ISO standard (ISO 11426) and is the method the London Bullion Market Association requires for accreditation to its Good Delivery List.

The process is destructive and takes several hours. A small representative sample is drilled from the lot, weighed to microgram precision, mixed with lead and flux, and melted in a furnace. The molten lead absorbs the gold and silver while the flux carries away base metals as slag. The lead-gold bead is then transferred to a porous ceramic cup called a cupel and heated in an oxidizing atmosphere. The lead oxidizes and is absorbed by the cupel. What remains is a tiny bead of gold and silver alloy. The silver is dissolved away with nitric acid (a step called “parting”), leaving pure gold that is weighed on a microbalance.

The math is straightforward: the final gold weight divided by the original sample weight, expressed as a decimal, is the fineness. Skilled fire assayers routinely achieve accuracy within two parts per ten thousand (0.0002), which is why the method is the arbitration standard when refiners and clients disagree over a result.

The downsides are cost and time. A single fire assay typically runs $30 to $75 per determination and requires a full working day. Refiners batch this work and absorb the cost into the refining fee for large lots. For a single ring or a few coins, fire assay is disproportionately expensive, which is why other methods are used at the retail end.

XRF: fast, non-destructive, surface-limited

X-ray fluorescence spectroscopy is the tool you see in pawn shops, coin dealers, and refiner intake stations. A handheld or benchtop unit bombards the metal with X-rays. The atoms in the sample fluoresce, emitting secondary X-rays at wavelengths characteristic of each element. A detector measures the intensities and calculates the alloy composition in seconds.

XRF is non-destructive and requires no sample preparation beyond a clean surface. That is a major advantage for finished jewelry, numismatic coins, and small bars where cutting a sample would destroy value. Modern XRF analyzers achieve accuracy of about 0.1 to 0.5 percent on gold content when properly calibrated, which is more than adequate for retail buying decisions.

The critical limitation is that XRF only reads the surface, typically the top 10 to 50 micrometers. A gold-plated piece over base metal will read as pure gold on the surface while being nearly worthless underneath. A tungsten-cored fake bar, because tungsten has almost the same density as gold, can also pass a surface XRF test on gold-plated faces. This is why serious refiners do not rely on XRF alone for lots above a certain size. They melt the material first, homogenize it, then either assay a chip of the resulting bar by fire or run confirmatory XRF on a fresh interior surface.

ICP: for trace elements and silver

Inductively coupled plasma spectroscopy comes in two flavors: ICP-OES (optical emission) and ICP-MS (mass spectrometry). Both dissolve a sample in acid and inject the solution into an argon plasma torch at temperatures near 10,000 kelvin. The excited atoms emit or ionize, and detectors quantify each element separately.

ICP is the reference method for silver assay (ISO 15093 covers silver, platinum, and palladium content by ICP) and for measuring trace impurities in refined gold, such as copper, iron, and platinum-group metals at parts-per-million levels. Refiners use ICP when a buyer specifies a purity certificate that documents not just “99.99 percent gold” but the specific balance of trace elements. Semiconductor customers and some central banks require this level of detail. It is rarely relevant to retail scrap sellers.

What the three methods look like side by side

Assay cards on bars: what they certify

Most small investment bars (1 gram to 10 ounces) ship inside a sealed plastic assay card, sometimes called a certicard or CertiPAMP after PAMP Suisse’s version. The card is not decoration. It is a documented statement by the refiner of that specific bar’s serial number, weight, fineness, and the assayer who verified it.

A genuine assay card typically shows the refiner’s logo and name, the bar’s unique serial number (matched to the number stamped on the bar itself), the stated fine weight in grams or troy ounces, the fineness (usually 999.9 for a modern investment bar), the assayer’s printed name and signature, and often a hologram or other tamper-evident feature. The plastic housing is heat-sealed. Breaking the seal does not destroy the bar’s purity, but it can reduce resale value because many dealers will re-assay unsealed bars before making an offer.

For gold IRA investors, this documentation chain is what allows an IRS-approved depository to accept a bar into custody without re-assaying it on intake. The card and hallmarks together satisfy the depository’s verification requirements.

How refiners buy scrap

The classic refiner intake workflow has five steps:

1. Receiving and weighing. The lot is signed in at the loading dock, given a job number, and gross-weighed on a certified scale. The customer receives a signed receipt with the incoming weight.
2. Sorting. Karat gold, sterling silver, platinum, filled and plated pieces, and non-metallic contaminants (stones, plastic, findings) are separated. Some refiners charge separately for stone removal or discard low-yield material.
3. Melting and homogenization. Each metal category is melted together into a single “melt bar.” This is essential because scrap is heterogeneous. A pile of rings averaging 14K might contain some 10K, some 18K, and some plated pieces. Only after melting can a representative sample be taken.
4. Sampling and assay. A pin or chip is drilled from the melt bar. This sample is fire-assayed or XRF-tested against the melt bar cross-section. The result multiplied by the melt bar weight gives the gold content of the entire lot.
5. Settlement. The customer receives a settlement statement listing gross weight in, fine weight recovered (assayed gold content), the payout basis (usually a percentage of the LBMA PM spot price on a specified day), fees deducted, and net payment. Payment is typically wired within one to five business days after the customer approves the settlement.

Some refiners offer a “melt only” option where the customer receives refined bars back instead of cash. This is more common for jewelry manufacturers and dental labs than for individual sellers, but it is available.

Refining fees and minimum lot sizes

Refining fees are not a single number. A typical structure has four components:

• Treatment charge. A per-ounce or per-kilogram fee for the refining work itself. This is the largest component. It typically scales down as lot size increases, which is why refiners quote different rates for one ounce than for one hundred ounces.
• Assay fee. A flat charge per lot or per determination, often around $30 to $100 depending on the method and the number of confirmations required.
• Percentage of fine content retained. Some refiners deduct a small percentage (often 1 to 5 percent, less for large lots) of the recovered gold rather than charging a flat treatment fee. Others combine both. The percentage should be disclosed on the quote.
• Freight and insurance. The seller usually ships insured. Insured freight for a lot worth $10,000 through a specialty carrier such as Brink’s or Malca-Amit can be several hundred dollars, though smaller lots often ship through registered mail or Federal Express with declared value.

Minimum lot sizes vary sharply. Major precious metals refiners such as Metalor, Asahi Refining, Umicore, and Heraeus typically set minimums at one troy ounce of contained gold, sometimes higher for advantaged pricing. Small independent refiners and larger jewelry-industry buyers accept lots as small as one gram, but the effective payout drops steeply below about an ounce because fixed assay and freight costs consume a larger share of the value.

Ask any refiner for a written schedule before you ship. Verbal quotes are difficult to enforce if the settlement statement contains surprises.

Why refiners pay close to spot

A refiner sits at the end of the scrap-to-bullion supply chain. There is no intermediary standing between them and the world market for pure gold. That structural position is the main reason their payout can approach spot on qualifying lots.

Consider the alternative chain. When you sell a ring to a local pawn shop, the pawn shop pays you a price, then either resells intact to another consumer at retail (best margin) or, more often, sells the piece in bulk to a wholesaler. The wholesaler consolidates lots and sells to a refiner. Each intermediary needs a margin. By the time your ring has passed through three hands to reach a refiner, the cumulative margin absorbed is typically 30 to 50 percent of the metal’s spot value.

Selling direct to a refiner removes those layers. The refiner’s own margin, expressed as the difference between spot and payout, is typically 2 to 10 percent depending on volume, plus the flat fees discussed above. On a $10,000 lot, that spread is a few hundred dollars rather than a few thousand.

The catch is that refiners are wholesale businesses. They expect professional-grade counterparties: correctly sorted material, clean documentation, willingness to ship, and patience for a multi-day settlement cycle. Consumers looking for cash the same afternoon are better served by a local buyer who accepts the pawn-and-flip margin as the cost of speed and convenience.

When a refiner is the right choice

Direct refiner sale makes sense when:

• Your lot exceeds roughly ten troy ounces of contained gold (about $30,000 at typical current spot). Below that, fees and freight erode the advantage.
• You have documented, sorted material (dental lab gold, jeweler’s bench sweep, estate lots that have already been categorized).
• You can wait one to two weeks between shipment and payment.
• You are comfortable arranging insured freight and reviewing a technical settlement statement.

For everything else, a competitive local process (multiple offers, XRF verification in your presence, cash or wire same day) is usually the better trade-off between price and convenience. That is the model the FTC discusses in its consumer guidance on selling gold, which emphasizes getting multiple offers, understanding how the buyer arrived at their price, and never handing over the piece before agreeing on a number.