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The fineness of a precious metal object (coin, bar, jewelry, etc.) represents the weight of fine metal therein, in proportion to the total weight which includes alloying base metals and any impurities. Alloy metals are added to increase hardness and durability of coins and jewelry, alter colors, decrease the cost per weight, or avoid the cost of high-purity refinement. For example, copper is added to the precious metal silver to make a more durable alloy for use in coins, housewares and jewelry. Coin silver, which was used for making silver coins in the past, contains 90% silver and 10% copper, by mass. Sterling silver contains 92.5% silver and 7.5% of other metals, usually copper, by mass.

Various ways of expressing fineness have been used and two remain in common use: millesimal fineness expressed in units of parts per 1,000[1] and karats or carats used only for gold. Karats measure the parts per 24, so that 18 karat = 18⁄24 = 75% gold and 24 karat gold is considered 100% gold.[2]

Millesimal fineness

[edit]

Millesimal fineness is a system of denoting the purity of platinum, gold and silver alloys by parts per thousand of pure metal by mass in the alloy. For example, an alloy containing 75% gold is denoted as "750". Many European countries use decimal hallmark stamps (i.e., "585", "750", etc.) rather than "14 k", "18 k", etc., which is used in the United States, and the United Kingdom prior to the 1970s.

It is an extension of the older karat system of denoting the purity of gold by fractions of 24, such as "18 karat" for an alloy with 75% (18 parts per 24) pure gold by mass.

The millesimal fineness is usually rounded to a three figure number, particularly where used as a hallmark, and the fineness may vary slightly from the traditional versions of purity.

Here are the most common millesimal finenesses used for precious metals and the most common terms associated with them.

Platinum

[edit]
  • 999.95: what most dealers would buy as if 100% pure; the most common purity for platinum bullion coins and bars
  • 999—three nines fine
  • 950: the most common purity for platinum jewelry
  • 900—one nine fine
  • 850
  • 750

Gold

[edit]
1 troy ounce of four nines fine gold (999.9)
  • 999.999—six nines fine: The purest gold ever produced. Refined by the Perth Mint in 1957.[3][4]
  • 999.99—five nines fine: The purest type of gold currently produced; the Royal Canadian Mint regularly produces commemorative coins in this fineness, including the world's largest, at 100 kg.[5]
  • 999.9—four nines fine: Most popular. E.g. ordinary Canadian Gold Maple Leaf and American Buffalo coins.
  • 999—24 karat, also occasionally known as three nines fine: e.g., Chinese Gold Panda coins.
  • 995: The minimum allowed in Good Delivery gold bars.
  • 990—two nines fine
  • 986—Ducat fineness: Formerly used by Venetian and Holy Roman Empire mints; still in use in Austria and Hungary.
  • 965: Thai standard for gold purity. Often considered equivalent to 23 karat in this context.[6]
  • 958—23 karat
  • 916—22 karat: Crown gold. Historically common for bullion coins, and currently used for British Sovereigns, South African Krugerrands, and the modern (1986—present) American Gold Eagles. Standard for jewelry in some countries such as India.[7]
  • 900—one nine fine: American Eagle denominations for 1837–1933; currently used in Latin Monetary Union mintage (e.g. French and Swiss "Napoleon coin" 20 francs).
  • 899—American Eagles briefly for 1834–1836.
  • 834—20 karat
  • 750—18 karat: Typical fineness for modern jewelry in most of Europe.[8] Even in regions where higher purities are common, this is the maximum fineness used for gemstone-set jewelry, as the metal must be hard enough to robustly hold the stone in place.[9]
  • 625—15 karat
  • 585—14 karat: Most common fineness for jewelry in the United States.[10] While 14 karat is more precisely 583.3 fine, this level is not generally used in decimal fineness.
  • 500—12 karat
  • 417—10 karat: Historically, the minimum standard for gold in the US. As of August 2018, any marked karat is permissible.
  • 375—9 karat: Minimum standard for gold in some of the Commonwealth realms: Australia, Canada, New Zealand, UK, etc. It is also the minimum in Austria, Ireland, Portugal and France.
  • 333—8 karat: Minimum standard for gold in Germany after 1884.[11] It is also the minimum for Denmark, Greece and Mexico.
  • 042–1 karat: Legal minimum for gold in the US since the revision of the FTC Guides of August 2018.

Silver

[edit]
See also: Silver standards
A 2019 American Silver Eagle bullion coin with a fineness of 999 (three nines fine), together with a Walking Liberty half dollar with a fineness of 900 (one nine fine); this latter alloy is also often referred to as 90% silver or coin silver.
  • 999.99—five nines fine: The purest silver ever produced. This was achieved by the Royal Silver Company of Bolivia.[12]
  • 999.9—four nines fine: ultra-fine silver used by the Royal Canadian Mint for their Silver Maple Leaf and other silver coins
  • 999—fine silver or three nines fine: used in Good Delivery bullion bars and most current silver bullion coins. Used in U.S. silver commemorative coins and silver proof coins starting in 2019.[13]
  • 980: common standard used in Mexico ca. 1930–1945
  • 958: (23⁄24) Britannia silver[14]
  • 950: French 1st Standard
  • 947.9: 91 zolotnik Russian silver
  • 935: Swiss standard for watchcases after 1887, to meet the British Merchandise Marks Act and to be of equal grade to 925 sterling. Sometimes claimed to have arisen as a Swiss misunderstanding of the standard required for British sterling. Usually marked with three Swiss bears.
  • 935: used in the Art Deco period in Austria and Germany. Scandinavian silver jewellers used 935 silver after the 2nd World War
  • 925: (37⁄40) Sterling silver. The UK has used this alloy from the early 12th century. Equivalent to plata de primera ley in Spain (first law silver)
  • 917: a standard used for the minting of Indian silver (rupees), during the British raj and for some coins during the first Brazilian Republic.
  • 916: 88 zolotnik Russian silver
  • 900: one nine fine, coin silver, or 90% silver: e.g. Flowing Hair and 1837–1964 U.S. silver coins. Also used in U.S. silver commemorative coins and silver proof coins 1982–2018.
  • 892.4: US coinage 1485⁄1664 fine "standard silver" as defined by the Coinage Act of 1792: e.g. Draped Bust and Capped Bust U.S. silver coins (1795–1836)
  • 875: 84 zolotnik is the most common fineness for Russian silver. Swiss standard, commonly used for export watchcases (also 800 and later 935).
  • 868: 83 1⁄3 zolotnik. Imperial Russian coinage between 1797[15] and 1885.[16]
  • 835: A standard predominantly used in Germany after 1884, and for some Dutch silver; and for the minting of coins in countries of the Latin Monetary Union
  • 833: (5⁄6) a common standard for continental silver especially among the Dutch, Swedish, and Germans
  • 830: A common standard used in older Scandinavian silver
  • 800: The minimum standard for silver in Germany after 1884; the French 2nd standard for silver; "plata de segunda ley" in Spain (second law silver); Egyptian silver; Canadian silver circulating coinage from 1920 to 1966/7[17] Used for the outer cladding of US half dollars between 1965 and 1970, and commemorative issue Eisenhower dollars between 1971 and 1978 (cores are 20.9% silver)
  • 750: An uncommon silver standard found in older German, Swiss and Austro-Hungarian silver
  • 720: Decoplata:[18] many Mexican and Dutch silver coins use this standard, as well as some coins from Portugal's former colonies,[19] Japan,[20] Uruguay,[21] Ecuador, Egypt, and Morocco.
  • 600: Used in some examples of postwar Japanese coins, such as the 1957-1966 100 yen coin
  • 500: Standard used for making British coinage 1920–1946 as well as Canadian coins from 1967 to 1968, and some coins from Colombia and Brazil.
  • 350: Standard used for US Jefferson "war nickels" minted between 1942 and 1945.

Carat

[edit]
"Karat" redirects here. For other uses, see Karat (disambiguation).

The carat (UK spelling, symbol c or Ct) or karat (US spelling, symbol k or Kt) [22][23] is a fractional measure of purity for gold alloys, in parts fine per 24 parts whole. The carat system is a standard adopted by US federal law.[24]

Mass

[edit]
C = 24 × (Mg / Mm)

where

C is the carat rating of the material,
Mg is the mass of pure gold in the alloy, and
Mm is the total mass of the material.

24-carat gold is pure (while 100% purity is very difficult to attain, 24-carat as a designation is permitted in commerce for a minimum of 99.95% purity), 18-carat gold is 18 parts gold, 6 parts another metal (forming an alloy with 75% gold), 12-carat gold is 12 parts gold (12 parts another metal), and so forth.[25]

In Britain, the carat was divisible into four grains, and the grain was divisible into four quarts. For example, a gold alloy of 127⁄128 fineness (that is, 99.2% purity) could have been described as being 23-carat, 3-grain, 1-quart gold.

The carat fractional system is increasingly being complemented or superseded by the millesimal system, described above for bullion, though jewelry generally tends to still use the carat system.

Conversion between percentage of pure gold and karats:

  • 58.33–62.50% = 14 c (acclaimed 58.33%)
  • 75.00–79.16% = 18 c (acclaimed 75.00%)
  • 91.66–95.83% = 22 c (acclaimed 91.66%)
  • 95.83–99.95% = 23 c (acclaimed 95.83%)
  • 99.95–100% = 24 c (acclaimed 99.95%)

Volume

[edit]

However, this system of calculation gives only the mass of pure gold contained in an alloy. The term 18-carat gold means that the alloy's mass consists of 75% of gold and 25% of other metals. The quantity of gold by volume in a less-than-24-carat gold alloy differs according to the alloys used. For example, knowing that standard 18-carat yellow gold consists of 75% gold, 12.5% silver and the remaining 12.5% of copper (all by mass), the volume of pure gold in this alloy will be 60% since gold is much denser than the other metals used: 19.32 g/cm3 for gold, 10.49 g/cm3 for silver and 8.96 g/cm3 for copper.

Etymology

[edit]
Carob (Ceratonia siliqua) pod and seeds, origin of carat via Arabic qīrāṭ which itself comes from the Greek word for the seed kerátion

Karat is a variant of carat. First attested in English in the mid-15th century, the word carat came from Middle French carat, in turn derived either from Italian carato or Medieval Latin carratus. These were borrowed into Medieval Europe from the Arabic qīrāṭ meaning "fruit of the carob tree", also "weight of 5 grains", (قيراط) and was a unit of mass[26] though it was probably not used to measure gold in classical times.[27] The Arabic term ultimately originates from the Greek kerátion (κεράτιον) meaning carob seed (literally "small horn")[27][28][29] (diminutive of κέρας – kéras, "horn"[30]).

In 309 AD, Roman Emperor Constantine I began to mint a new gold coin, the solidus, that was 1⁄72 of a libra (Roman pound) of gold[31] equal to a mass of 24 siliquae, where each siliqua (or carat) was 1⁄1728 of a libra.[32] This is believed to be the origin of the value of the karat.[33]

Verifying fineness

[edit]

While there are many methods of detecting fake precious metals, there are realistically only two options available for verifying the marked fineness of metal as being reasonably accurate: assaying the metal (which requires destroying it), or using X-ray fluorescence (XRF). XRF will measure only the outermost portion of the piece of metal and so may get misled by thick plating.

That becomes a concern because it would be possible for an unscrupulous refiner to produce precious metals bars that are slightly less pure than marked on the bar. A refiner doing $1 billion of business each year that marked .980 pure bars as .999 fine would make about an extra $20 million in profit. In the United States, the actual purity of gold articles must be no more than .003 less than the marked purity (e.g. .996 fine for gold marked .999 fine), and the actual purity of silver articles must be no more than .004 less than the marked purity.[34]

Fine weight

[edit]

A piece of alloy metal containing a precious metal may also have the weight of its precious component referred to as its "fine weight". For example, 1 troy ounce of 18 karat gold (which is 750 ‰ gold) may be said to have a fine weight of 0.75 troy ounces.

Most modern government-issued bullion coins specify their fine weight. For example, the American Gold Eagle is embossed One Oz. Fine Gold and weighs 1.091 troy oz.

Troy mass of silver content

[edit]

Fineness of silver in Britain was traditionally expressed as the mass of silver expressed in troy ounces and pennyweights (1⁄20 troy ounce) in one troy pound (12 troy ounces) of the resulting alloy. Britannia silver has a fineness of 11 ounces, 10 pennyweights, or about silver, whereas sterling silver has a fineness of 11 ounces, 2 pennyweights, or exactly silver.

See also

[edit]

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Fineness

View on Grokipedia
from Grokipedia
Fineness is a numerical measure of the purity of a , indicating the proportion of pure metal present relative to the total mass, typically expressed in parts per thousand (millesimal fineness) or as a decimal fraction. In the context of , fineness is often correlated with the carat system, where 24 carats represent 999 fineness (99.9% pure ), while lower grades such as 18 carat (750 fineness or 75% pure) and 14 carat (585 fineness or 58.5% pure) incorporate like or silver for enhanced durability in jewelry and other applications. For silver, fineness denotes levels such as 999 (fine silver, 99.9% pure) used in most bullion and as the LBMA minimum, with some products achieving 999.9 (99.99% pure) for ultra-high purity, 925 (sterling silver, 92.5% pure) common in jewelry, and 900 (coin silver, 90% pure) historically used in minting. International standards govern acceptable fineness to ensure quality and trade integrity; for instance, the London Bullion Market Association (LBMA) mandates a minimum of 995 fineness for bars in its List, while silver must reach 999 fineness. The (ISO) through documents like ISO 9202 recommends fineness ranges for jewelry alloys, such as 375 to 999 for and 800 to 999 for silver, promoting consistency across global markets. Fineness is verified through hallmarks on items or assays using methods like energy-dispersive (ED-XRF), as outlined in ISO 23345, allowing non-destructive confirmation of purity in finished products. Higher fineness generally correlates with greater value and is crucial for investment-grade , though alloys with lower fineness balance purity with practical properties like .

Definition and Fundamentals

Definition of fineness

Fineness refers to the proportion of pure , such as , silver, or , present by weight in an , typically accounting for the addition of base metals and impurities. This measure indicates the purity level of the , where higher fineness signifies a greater content of the valuable metal relative to the total mass. It is commonly expressed as a , , or in parts per thousand, with systems like millesimal fineness (parts per 1,000) and the karat system serving as standard methods for notation. Alloying precious metals with base metals is primarily done to enhance properties such as , as pure forms are often too soft for practical use; for instance, is added to to increase its hardness for jewelry and s. Other purposes include altering the color of the alloy or reducing production costs by incorporating less expensive metals. Representative examples include silver, which contains 90% pure silver alloyed with 10% for improved strength in minting, and , comprising 92.5% pure silver with the remainder typically to boost wear resistance. Unlike measures of total mass or volume, fineness specifically quantifies the purity of the component within the , focusing solely on the weight ratio of the fine metal to the whole. This distinction ensures that fineness serves as a precise indicator of value and quality in and , independent of the alloy's overall or .

Importance in alloys and trade

Standardized fineness has played a crucial role in preventing and ensuring the intrinsic value of precious metals in throughout . In , the began with a high fineness of approximately 3.65 grams of pure silver in the late Republic, but repeated debasements reduced this to as low as 1.5 grams by the time of Caracalla, leading to economic instability and loss of public trust in the currency. Such practices prompted the development of purity mandates, exemplified by England's introduction of hallmarking in 1300 to guarantee silver purity and protect against adulteration in commercial exchanges. These early regulations facilitated international by establishing verifiable standards that reduced the risk of counterfeiting and enabled cross-border confidence in metal value. In modern commerce, standardized fineness continues to safeguard consumers and promote global exchange by mandating minimum purity levels for traded articles. The 1972 Vienna Convention on the Control and Marking of Articles of Precious Metals, which entered into force in 1975, harmonizes and marking requirements among signatory nations to prevent misrepresentation while streamlining legitimate trade in jewelry, coins, and . Systems such as millesimal fineness and the karat scale provide precise notations of composition, allowing buyers to assess true worth without specialized testing. This framework has been essential in curbing illicit activities, as unregulated low-fineness metals can undermine market integrity and inflate costs through deceptive practices. Controlled fineness is vital in industrial alloys for balancing performance properties with economic viability across sectors. In jewelry manufacturing, pure precious metals are too soft for everyday wear, so alloys with specified fineness—typically 14 to 18 karats for —enhance while retaining aesthetic appeal and value. In , alloys of high fineness (often 99.99% pure or thinly plated) are employed for their superior electrical conductivity and resistance, ensuring reliable connections in circuit boards and connectors despite the higher cost compared to base metals. For dental applications, alloys with precise fineness levels, such as high-noble compositions exceeding 60% precious metals, are selected for their , minimizing ion release and allergic reactions in oral environments. The economic implications of fineness underscore its regulatory importance, as higher purity directly influences in markets while alloys optimize cost-effectiveness for practical use. Articles with elevated fineness command greater value due to their higher content, driving demand in investment-grade and , yet alloying reduces material expenses without compromising essential traits like strength or conductivity. This balance has evolved through international agreements like the Vienna Convention, which supports by enforcing consistent standards and mitigating the economic disruptions caused by historical debasements.

Measurement Systems

Millesimal fineness

Millesimal fineness is a for denoting the purity of alloys by expressing the proportion of pure metal in parts per thousand (‰) of the total mass. For instance, an alloy marked as 750 millesimals contains 750 parts pure metal and 250 parts alloying elements per 1,000 parts total, equivalent to 75% purity or a fineness of 0.750. This metric is widely preferred in and for trading due to its precision, which facilitates accurate international . The primary advantages of the millesimal system over alternatives, such as the karat method used primarily for , lie in its ability to specify fine gradations of purity. It supports markings like 999.9 for near-pure alloys, enabling distinctions at levels as precise as 0.1 parts per thousand, which is essential for high-value applications. Additionally, millesimal values are commonly incorporated into hallmarking stamps on jewelry and to certify compliance with legal purity standards. To convert between formats, multiply the percentage purity by 10 to obtain the millesimal value; for example, 99.9% purity yields 999 millesimals. This straightforward scaling aligns with the decimal basis of the . The millesimal fineness emerged in 19th-century as part of broader efforts to standardize trade through decimal metrics, addressing inconsistencies in earlier fractional notations. It gained formal recognition through international agreements, such as ISO 9202, which specifies permissible fineness ranges for alloys to ensure uniformity across borders.

Karat system

The karat system measures the purity of in an by expressing it as parts of pure per 24 parts of the total . For instance, 18-karat contains 18 parts pure and 6 parts other metals, equivalent to 75% by . The purity in karats is calculated using the : karats = 24 × ( of pure / total of ). This is specific to and distinguishes it from the millesimal fineness scale, where equivalents like 18K correspond to 750 parts per thousand. Common karat grades include 24K, which represents 99.9% or higher pure ; 22K at 91.7%; 18K at 75%; 14K at 58.3%; and 10K at 41.7%. These grades balance durability and appearance through alloying, with compositions varying by color. For example, 18K yellow typically consists of 75% , 15% silver, and 10% , while 18K typically consists of 75% , approximately 22.25% , and 2.75% silver. Legal minimums for items labeled as differ by country, such as 10K in the United States and 9K in the United Kingdom. The term "karat" derives from the Greek kerátion, meaning "carob seed," which ancient traders used as a uniform small weight due to its consistent size. This evolved through the Arabic qīrāṭ—referring to the carob fruit or pod—and entered European languages via Medieval Latin carratus and Italian carato by the 14th century, eventually denoting gold fineness as a proportion of 24 parts by the 1550s. While effective for gold jewelry, the karat system is less precise than millesimal fineness due to its fixed 24-part denominator, limiting granularity to increments of about 4.17%. It is also not used for non-gold metals like silver and is complemented by millesimal markings, which provide greater standardization for bullion trading and other applications, though karat remains prevalent in jewelry markets.

Standards for Precious Metals

Gold

Gold fineness standards specify the purity of gold in alloys used for bullion, coins, and jewelry, typically expressed in millesimal fineness (parts per thousand) or karats (parts per 24). For bullion and investment bars, 999.9 fineness, equivalent to 24 karats, represents nearly pure gold and is the standard for high-value products like those meeting London Bullion Market Association (LBMA) good delivery requirements, which mandate a minimum of 995 fineness. The highest recorded purity, 999.999 fineness, was achieved by the Perth Mint in 1957 with a proof plate, marking a milestone in refining technology. In jewelry, 750 fineness (18 karats, 75% pure ) is widely used for its balance of durability and luster, while 585 fineness (14 karats, 58.5% pure) serves budget options with greater resistance to wear. Legal minima vary: in the United States, items labeled as "gold" must meet at least 417 fineness (10 karats), enforced by guidelines. The European Union sets a 375 fineness (9 karats) threshold for gold designation in countries like the and , allowing lower-purity alloys. In , particularly and , 916 fineness (22 karats, 91.6% pure) is common for traditional jewelry due to cultural preferences for higher gold content. Specifically, in Hong Kong, gold jewelry primarily uses 999 fineness or higher, with items labeled "Chuk Kam" (pure gold) requiring at least 999/1000 parts by weight. In Shanghai, China, national standards specify 999 or 999.9 fineness for pure gold jewelry. In New York, mainstream jewelry typically employs 585 (14 karat) or 750 (18 karat) fineness for enhanced durability, though 999 (24 karat) pure gold is available, particularly in Chinese districts. Alloying elements influence gold's color and properties at standard fineness levels; for instance, white gold at 750 fineness incorporates or to achieve a silvery hue, with palladium providing a alternative to nickel. These alloys enhance without significantly altering the base purity, enabling varied like yellow, rose, or white gold while maintaining the specified fineness. Historically, alloys evolved from ancient , a natural -silver mixture with variable fineness of 40-90% used in early coins from regions like around 600 BCE, to modern refining techniques that enable consistent high-purity standards. This progression reflects advances in , from rudimentary separation methods to electrolytic refining for today.

Silver

Silver fineness standards specify the purity of silver in alloys, typically expressed in millesimal notation as parts per thousand of pure silver. For , the accepted standard is 999 fine silver, meaning 99.9% pure silver, which ensures high purity for investment-grade bars and coins traded on international markets. Higher purity levels such as 999.9 (also denoted as .9999 or 99.99% pure silver) exist, with 999.9 parts per thousand silver and only 0.01% impurities. This ultra-fine purity requires additional refining steps and is used in certain premium products, such as some bars and coins from the Royal Canadian Mint. While 999.9 silver has ten times fewer impurities than 999, the difference is negligible for most investment, industrial, or jewelry applications, where 999 remains the standard for investment-grade bullion and the minimum required for LBMA Good Delivery silver bars. , the most common alloy for jewelry and decorative items, has a fineness of 925, consisting of 92.5% silver alloyed with 7.5% to enhance and reduce tarnishing. In , silver historically used a 900 fineness (90% silver and 10% ) for circulating coins until 1965, when production shifted to base metals clad over pure . Continental European silver often adheres to an 800 fineness standard (80% silver), which was prevalent in countries like and for and ornaments due to its cost-effectiveness and sufficient malleability. Regional variations reflect historical trade practices and regulatory preferences. In the , maintains a higher fineness of 958 (95.8% silver), introduced in as a response to coinage shortages and used primarily for high-end silverware until the . Mexican silverwork, particularly from artisans in the mid-20th century, frequently employed a 980 fineness (98% silver), offering greater purity than sterling while remaining workable for intricate jewelry and decorative pieces. In , the recognizes a range of fineness levels for hallmarked silver under the revised IS 2112:2025, including 800, 835, 925, 958, 970, 990, and 999, allowing flexibility for traditional jewelry and artifacts while ensuring consumer protection through mandatory marking since September 2025. These standards support diverse applications based on required purity and alloy properties. Sterling silver (925 fineness) dominates and flatware production, as the copper addition provides strength for everyday use without compromising luster. Fine silver at 999 fineness is essential for , where pure silver halides like are used in light-sensitive emulsions for film and radiographic plates, demanding minimal impurities to ensure chemical reactivity. U.S. coin silver at 900 fineness was standard for pre-1965 circulating silver , balancing wear resistance with sufficient silver content for monetary value. Historically, silver fineness has varied with economic pressures, as seen in the Roman , introduced around 211 BCE initially at nearly 98% silver purity (about 4.5 grams of silver per coin) to facilitate and payments. Over centuries, progressive reduced its fineness—dropping to around 89% by the CE and further to below 50% by the —due to fiscal demands, , and silver shortages, illustrating early challenges in maintaining metallic standards.
StandardFinenessTypical AlloyPrimary UseRegion/Example
Fine/Bullion999Nearly pure Ag, photographyGlobal (LBMA)
Sterling92592.5% Ag + 7.5% CuJewelry, tablewareUK, US,
Coin90090% Ag + 10% CuCoins (pre-1965)
Continental80080% Ag + 20% otherOrnaments, hollowware (, )
Britannia95895.8% Ag + 4.2% CuHigh-end silverware
Mexican98098% Ag + 2% CuJewelry, decor ()

Platinum and other platinum-group metals

Platinum-group metals (PGMs), which include , , , , , and , are characterized by their high melting points, exceptional corrosion resistance, and chemical inertness, making them suitable for demanding industrial environments. These properties enable PGMs to maintain integrity under extreme conditions, such as high temperatures and exposure to harsh chemicals. Fineness standards for PGMs are typically expressed using the millesimal system, indicating purity in parts per thousand. For , investment-grade and bars require a minimum fineness of 999.5 (99.95% pure), as established by the London Platinum and Palladium Market (LPPM) and aligned with standards from the (NYMEX). In jewelry applications, is commonly alloyed to a fineness of 950 (95% pure), often with small additions of or to enhance durability and workability while preserving its qualities. Industrial uses, such as in chemical processing equipment and electrical contacts, frequently employ 900 fineness (90% pure) alloys to balance cost and performance. Palladium follows similar high-purity benchmarks for , with standards mandating 999.5 fineness for bars used in and wholesale trading. Jewelry alloys range from 500 to 950 fineness, where 950 is prevalent for its whiteness and strength, alloyed with silver or other PGMs. , primarily utilized in industrial settings rather than or jewelry, achieves 999.9 fineness (99.99% pure) for catalytic applications, ensuring maximal efficiency in emission control. In automotive catalysts, palladium is applied at 999 fineness to oxidize carbon monoxide and hydrocarbons in exhaust gases, comprising a significant portion of global demand. Platinum at 999.5 fineness is vital in medical devices, such as pacemakers and implants, due to its biocompatibility and resistance to bodily fluids. Recycled PGMs must meet the same good delivery fineness standards of 999.5 as primary materials to qualify for LPPM lists, supporting circular supply chains in automotive and electronics sectors under responsible sourcing frameworks like the LPPM Responsible Sourcing Programme.

Verification and Assay

Traditional methods

Traditional methods of verifying the fineness of s primarily involved destructive or semi-destructive techniques that were developed over centuries to ensure quality in and craftsmanship. These approaches, while labor-intensive, provided essential assurance in eras before advanced , often requiring skilled ers to separate and quantify content from alloys. Fire , acid testing, and the touchstone method emerged as cornerstone practices, each with distinct procedures, historical roots, and inherent limitations such as sample destruction and operator dependency. Fire assay, one of the oldest and most precise traditional techniques, dates back to ancient civilizations but was refined and widely adopted in medieval for quantifying and silver in ores, , and . The process entails melting a sample with fluxes—such as , soda ash, and silica—in a to form a that captures impurities, followed by where the molten is oxidized in a porous cupel, allowing base metals to absorb into the cupel while leaving a of pure for weighing. This method achieves an accuracy of approximately ±0.5% for and silver fineness, making it the standard for destructive assays despite consuming the sample entirely. Its development addressed the need for reliable quantification in expanding medieval trade networks. The acid test, another destructive approach, relies on the differential solubility of base metals versus precious ones in acids to assess fineness, with origins tracing to alchemical practices in antiquity and standardization in the 18th century. A small filing or scratch from the sample is exposed to nitric acid, which dissolves copper and other impurities but leaves gold residue intact; for lower fineness alloys like 14-karat gold, stronger aqua regia (a mixture of nitric and hydrochloric acids) may be used to observe partial dissolution and residue characteristics. This method provides a qualitative to semi-quantitative evaluation but is limited by subjectivity in residue interpretation and potential false positives from surface plating. In contrast, the touchstone method offers a quicker, less invasive alternative, employed since ancient times—evidenced in Greek and Roman texts—for on-site fineness estimation without full sample destruction. The metal is rubbed on a smooth, fine-grained (typically or ) to produce a streak, which is then compared to streaks from reference s of known fineness after applying ; the color, persistence, and reaction speed indicate purity levels. While rapid and portable, it is approximate, with accuracy varying by alloy composition and assayer experience, often unreliable for very high fineness above 22 karats due to minimal differences in streak reactions. Historical standards for these assays evolved through institutional oversight to enforce consistent fineness in commerce. In the , assay offices established under the 1300 Statute of Edward I in —followed by offices in other cities—mandated assay verification for hallmarked and silver, with tolerances around ±5 millesimals to account for procedural variations, ensuring items met legal minima like 916 for 22-karat . Internationally, France's titre system, formalized post-1260 under royal decrees and centralized after the Revolution, similarly used and acid assays at regional bureaus to certify fineness in parts per thousand, such as 950 for first-grade silver, promoting trust in cross-border trade. These frameworks highlighted the methods' role in mitigating , though limitations like destruction and time intensified the push for refinements over time.

Modern techniques

Modern techniques for verifying the fineness of precious metals include non-destructive, minimally invasive, and destructive laboratory methods, with an emphasis on non-destructive approaches leveraging advanced and digital technologies to provide rapid, accurate assessments without always compromising the sample's . These approaches have revolutionized assaying in jewelry, , and , enabling on-site analysis and integration with global verification systems. X-ray fluorescence (XRF) is a cornerstone of contemporary fineness testing, analyzing surface composition by exciting atoms with X-rays and measuring the emitted fluorescent rays to determine elemental percentages. Portable handheld XRF devices, such as those from and Thermo Fisher, deliver non-destructive results in seconds, detecting elements like , silver, , and with accuracy typically within 0.1-0.2% of fire assay standards for homogeneous samples. These instruments are particularly suited for jewelry evaluation, identifying karat values, plating, and counterfeits through features like AuDIT technology, which combines XRF with electrical and thermal signatures, as outlined in standards like ISO 23345 for energy-dispersive XRF (ED-XRF). For higher precision in complex alloys, (ICP) optical emission dissolves a small sample portion in acid, atomizing it in a high-temperature plasma to produce emission spectra for multi-element quantification. ICP can simultaneously detect up to 70 elements, including trace impurities in precious metals, with detection limits in the parts-per-million range and relative standard deviations below 1% for major components like and silver. Widely used in laboratory settings for and certification, ICP-OES offers superior accuracy over surface-based techniques for heterogeneous materials. Laser-induced breakdown spectroscopy (LIBS) provides instant, in-situ analysis by focusing a pulse to vaporize a microscopic spot on the sample, creating a plasma whose reveals composition. Handheld LIBS instruments achieve limits of detection around 0.4-2.3 μg/g for silver and 0.8-1.1 μg/g for in ores and alloys, with prediction errors as low as 0.36 wt% for silver content in using multivariate . This technique excels in field applications for rapid purity screening, requiring no and enabling semi-quantitative assessment of fineness in minerals or finished products. Recent digital advancements further enhance these spectroscopic methods, including AI-driven processing for XRF data to improve quantitative accuracy in composition by fusing networks with spectral analysis, reducing matrix effects in gold-silver mixtures. integration provides immutable certification for , recording results and on decentralized ledgers to ensure from refinery to market, as adopted by organizations like the London Bullion Market Association. International standards, such as those from ASTM for XRF calibration in metal analysis and ISO for procedures, guide these techniques to maintain consistency across global trade. Hallmarks serve as complementary visual verification aids alongside these instrumental methods.

Fine weight

The fine weight of a refers to the mass of the pure metal content within it, calculated as the total mass of the multiplied by the fineness expressed as a decimal fraction. For instance, a 1 with a fineness of 0.750 contains 0.75 s of fine metal. This measure is essential for determining the intrinsic value of that include base metals for . The general formula for fine weight (FW) is FW = total weight (TW) × fineness (as decimal). For millesimal fineness, where purity is expressed in parts per thousand, this becomes FW = TW × (fineness / 1,000). For using the karat system, where 24 karats represent pure , the formula is FW = TW × (karats / 24). For example, in 1 gram of 14k gold, the fine weight is 1 × (14/24) ≈ 0.583 grams of pure gold; in practice, standard 14k gold is often 585 fineness (58.5% pure), yielding 0.585 grams of pure gold per gram. These calculations standardize the assessment of metal content across different purity notations. A practical example is the coin, which has a total weight of 1.091 ounces at 0.9167 fineness (22 karats), yielding exactly 1.000 ounce of fine . Similarly, a 1,000-gram silver bar stamped at 999 fineness contains 999 grams of fine silver, reflecting near-pure composition typical in products. For silver jewelry, such as sterling silver (925 fineness or 92.5% pure), the pure silver content is calculated by multiplying the total weight by 0.925. For example, a 250g piece would contain 231.25 grams of pure silver. Fine weight calculations underpin valuation by isolating the marketable pure metal quantity against spot prices, ensuring fair pricing in trade. They also inform yields, where refiners recover and quantify pure metal from scrap alloys to maximize economic return. ounces are commonly used for these computations in precious metals markets.

Troy mass of silver content

In the British system, silver fineness is historically expressed as the mass of pure silver in ounces and pennyweights contained within a pound of , where the pound equals 12 ounces or 240 pennyweights (with each ounce comprising 20 pennyweights). This method quantifies purity by specifying the pure silver content relative to the total mass, with the for fineness given as (pure pennyweights / 240) × 1000 to yield the millesimal value. The standard, at 92.5% purity or 925 millesimals, corresponds to 11 ounces and 2 pennyweights of pure silver (222 pennyweights total) per pound of . Similarly, the higher-purity standard, at approximately 95.8% or 958 millesimals, equates to 11 ounces and 10 pennyweights of pure silver (230 pennyweights total) per pound. These expressions allowed for precise assaying and hallmarking in traditional silversmithing, where deviations below the standard could result in penalties. This troy-based notation originated in medieval and persisted through pre-metric eras, particularly for coinage standardized under the sterling fineness following the Coinage Act of 1816, which formalized silver content in new mintings. Today, it serves primarily as a legacy reference, with modern standards favoring decimal millesimal notations like 925 for equivalents.

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