Troy weight


Troy weight is a system of units of mass that originated in 15th-century England, and is primarily used in the precious metals industry. The Troy weights are the grain, the pennyweight, the troy ounce, and the troy pound. The troy grain is equal to the grain-unit of the avoirdupois system, the troy ounce is heavier than the avoirdupois ounce, yet the troy pound is lighter than the avoirdupois pound.

Etymology

Troy weight probably takes its name from the French market town of Troyes in France where English merchants traded at least as early as the early 9th century. The name "troy" is first attested in 1390, describing the weight of a platter, in an account of the travels in Europe of the Earl of Derby.
Charles Moore Watson proposes an alternative etymology: The Assize of Weights and Measures, one of the statutes of uncertain date from the reign of either Henry III or Edward I, thus before 1307, specifies "troni ponderacionem"—which the Public Record Commissioners translate as "troy weight". The word "troni" refers to markets. Watson finds the dialect word "troi", meaning a balance in Wright's Dialect Dictionary. Troy weight referred to the tower system; the earliest reference to the modern troy weights is in 1414.

History

Many aspects of the troy weight system were indirectly derived from the Roman monetary system. The Romans used bronze bars of varying weights as currency. An aes grave weighed one pound. One twelfth of an aes grave was called an Ancient Roman units of measurement#Weight, or in English, an "ounce". Before the adoption of the metric system, many systems of troy weights were in use in various parts of Europe, among them Holland troy, Paris troy, etc. Their values varied from one another by up to several percentage points. Troy weights were first used in England in the 15th century, and were made official for gold and silver in 1527. The British Imperial system of weights and measures was established in 1824, prior to which the troy weight system was a subset of pre-Imperial English units.
The troy ounce in use today is essentially the same as the British Imperial troy ounce, adopted as an official weight standard for United States coinage by Act of Congress on May 19, 1828.
The British Imperial troy ounce was based on, and virtually identical with, the pre-1824 British troy ounce and the pre-1707 English troy ounce. Troy ounces have been used in England since about 1400 and the English troy ounce was officially adopted for coinage in 1527. Before that time, various sorts of troy ounces were in use on the continent.
The troy ounce and grain were also part of the apothecaries' system. This was long used in medicine, but has now been largely replaced by the metric system.
The only troy weight in widespread use today is the British Imperial troy ounce and its American counterpart. Both are currently based on a grain of 0.06479891 gram, with 480 grains to a troy ounce.
The British Empire abolished the 12-ounce troy pound in the 19th century, though it has been retained in the American system.

Origin

The origin of the troy weight system is unknown. Although the name probably comes from the Champagne fairs at Troyes, in northeastern France, the units themselves may be of more northern origin. English troy weights were nearly identical to the troy weight system of Bremen.
An alternative suggestion is that the weights come from the Muslim domains by way of the Gold Dirhem, in the manner that King Offa's weights were derived from the silver Dirhem.
According to Watson, troy relates to a dialect word troi. Then troy weight is a style of weighing, like auncel or bismar weights, or other kindred methods. The troy weight then refers to weighing of small precious or potent goods, such as bullion and medicines.

Use in other countries

Troy ounces are still often used in precious metal markets in countries that otherwise use International System of Units, except in East Asia. The People's Bank of China, in particular, which has never historically used troy measurements, has begun issuing Gold Pandas minted according to SI weights.

Units of measurement

Troy pound

The troy pound is 5760 grains, while an avoirdupois pound is approximately 21.53% heavier at 7000 grains.

Troy ounce (oz t)

Because of the International yard and pound agreement, one troy ounce equals exactly grams.
It also equals avoirdupois ounces, or exactly, about 10% larger.
The international yard and pound agreement did not define any troy weights. Rather, it defined the avoirdupois pound in metric terms, from which we can derive an exact value for the troy ounce. Specifically, it defined one pound as. We can derive an exact value for the troy ounce as follows:
An avoirdupois pound also equals 7,000 grains.

Pennyweight (dwt)

The pennyweight symbol is dwt. There are 24 grains in 1 pennyweights, and 20 pennyweights in one troy ounce. Because there were 12 troy ounces in the old troy pound, there would have been 240 pennyweights to the pound—the basis of the fact that the old pound-sterling contained 240 pence. However, prior to 1526, English pound sterling was based on the tower pound, which is of a troy pound. The d in dwt stands for denarius, the ancient Roman coin that equates loosely to a penny. The symbol d for penny can be recognized in the form of British pre-decimal pennies, in which pounds, shillings, and pence were indicated using the symbols £, s, and d, respectively.

Troy grain

Mint masses

Mint masses, also known as moneyers' masses were legalized by Act of Parliament dated 17 July 1649 entitled An Act touching the monies and coins of England. A grain is 20 mites, a mite is 24 droits, a droit is 20 perits, a perit is 24 blanks.

Scottish system

In Scotland, the Incorporation of Goldsmiths of the City of Edinburgh used a system in multiples of sixteen. Thus, there were 16 drops to the troy ounce, 16 ounces to the troy pound, and 16 pounds to the troy stone. The Scots had several other ways of measuring precious metals and gems, but this was the common usage for gold and silver.
The pound was 7,716 grains, but after the union, rounded to 7,680 grains. This divides to 16 ounces, each of 16 drops, each of 30 grains. The rounding makes the ounce and grain equal to the English standard.

Dutch system

The Dutch troy system is based on a mark of 8 ounces, the ounce of 20 engels, the Engel of 32 as. The mark was rated as 3,798 troy grains or 246.084 grammes. The divisions are identical to the tower system.

Conversions

The troy system was used in the apothecaries' system, but with different further subdivisions.

Relationship to British coinage

King Offa's currency reform replaced the sceat with the silver penny. This coin was derived from half of a silver dirhem. The masses were then derived by a count of coins, by a mix of Charlemagne and Roman systems. A shilling was set to twelve pence, an ounce to twenty pence, and a pound to twelve ounces or twenty shillings. The penny was quite a lot of money, so mass by coins was not a general practice.
Later kings debased the coin, both in weight and fineness. The original pound divided was the tower pound of 5,400 grains, but a later pound of 5,760 grains displaced it. Where once 240 pence made a tower pound, by the time of the United Kingdom Weights and Measures Act of 1824, a troy pound gives 792 silver pence, still minted as such as Maundy Money.
Sterling originally referred to the Norman silver penny of the late 11th century. The coin was minted to a fineness of 11 oz, 2 dwt, or 925 Millesimal fineness.