everything you ever needed to know about the Troy Ounce...
When someone speaks of something weighing an ounce, the chances are, that they are referring to an Avoirdupois Ounce. Unless, that is, they are referring to an ounce of gold, silver, platinum, gemstones or gunpowder: In which case, the chances are, they are referring to a Troy Ounce. The two ounces are not the same!
The prices of Gold, Silver and Platinum we hear quoted in the commodities markets, are for Troy Ounces. However, not everyone knows the difference; and if you are buying precious metals - for example gold bars online, or perhaps gold and silver on eBay (maybe with a view to profiting from an item's scrap value), you really need to be sure which type of ounce you are getting - because a Troy Ounce is over 9.7% heavier than an Avoirdupois Ounce!
An Avoirdupois Ounce is exactly 28.349523125 grams - or 437.5 grains
A Troy Ounce is exactly 31.1034768 grams - or 480 grains
Curiously, there are 12 Troy Ounces in a Troy Pound - and 16 Avoirdupois Ounces in an Avoirdupois Pound. So even though a Troy Ounce is heavier than an Avoirdupois Ounce, a Troy Pound is lighter than an Avoirdupois pound! However, the use of the Troy Pound has now been completely discontinued - thankfully for the sake of simplicity!
You also still sometimes see weights of silver bullion bars denoted in grains. (Grains are also still used in the USA in weights of certain armaments - for example, gunpowder, arrows and fencing foils.)
It's all a bit confusing, isn't it?
A little. But much less so than it must have been in ancient times. In days gone by there were other obscure systems of weights - such as the Wool Pound, Tower Pound, Mercantile Pound and London Pound - all of which are different! Most of these systems have been abolished for hundreds of years - but it is interesting to note the variations through time - and the complex challenges of maintaining "standard" weights that could be used by all. more on that in the "History of the Troy Ounce" section later.
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"Bullion coins" - such as Krugerrands, British Sovereigns and Canadian Maple Leafs are made from Silver, Gold or Platinum - and have been made at specific sizes in order to contain an exact amount of precious metal. A classic example are the United States Platinum "Eagles" - and these contain one Troy Ounce of "fine" (i.e. at least 99.9% pure) platinum.
Typically, modern bullion coins will state the amount of precious metal they contain in Troy Ounces, for example saying something like "one ounce fine gold" - but this will not necessarily mean that the coin itself weighs exactly an ounce. Krugerrands are made from 22 carat gold - 91.667% pure - and as such are made heavier than one ounce in order to contain exactly one Troy Ounce of gold. This can be slightly confusing - they are not made only of "fine gold" but contain exactly one ounce of "fine gold".
A British Sovereign is a bullion coin with a long and interesting history. The Sovereign was first minted in 1489 during Henry VII's reign - and the first sovereigns weighed half a Troy Ounce (240 grains) and were 23 carat - thus containing 230 grains of pure gold. However, the amount of gold in a sovereign was changed numerous times since then, eventually being fixed at 22 carat and 0.235421 Troy Ounces (113 grains) of actual gold, with the "Great Recoinage" of 1816.
The amount of precious metal contained in bullion coins is measured in Troy Ounces.
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Most non-bullion coins are not made with pure metal. Gold and Silver "currency" coins were typically made using alloys of other metals. One reason for this is because pure metals are often soft and therefore such coins would be easily damaged in ordinary circulation. Another reason is the obvious one that including less expensive metals in the mix makes such items cheaper to produce: and obviously, for regular currency, the value of the precious metal in a coin must not exceed the stated value of the coin - otherwise people will melt the coins down! In recent eras, the value of precious metals has far exceeded the monetary value of coins and so it is no longer appropriate to include precious metals in ordinary coins.
Prior to its abolishment in 1662, the method used in the UK to make coins was by hammering - and with various moneyers making coins under the auspices of various kings in less regulated times, the purity of such coins was often very variable. Not only this, but coins were often clipped and shaved in order to collect extra silver - sometimes so badly that 1/3 of the coin might have been clipped away. After this time "milled" coinage was introduced and coins were made with edge markings that made it impossible to clip them without it immediately showing.
From 1658 until 1920, British silver coins were made with 92.5% silver - known as "Sterling silver". Coins were often made with convenient weights of metal - thus a silver "Crown" of this time weighed around 27-30 grams; eventually settling by around 1820 on 28.3 grams - an Avoirdupois ounce. However, because such a crown was made with 92.5% silver, such a coin would therefore contain 28.3 x .925 = 26.1775 grams of pure silver: 0.8416261683 of a Troy ounce. A "half crown" from 1658-1920 weighed half an ounce - but similarly, contained less actual silver.
Dealers in silver scrap usually take these things into consideration, and the price of "silver scrap" will usually be correspondingly lower than the current "spot price" for silver. However, unless it is very badly worn or damaged, an old silver or gold coin usually has a higher resale value than the scrap value.
Between 1920 and 1946, British silver coins contain 50% silver - and after 1947, all silver in the ordinary coinage was removed and replaced with cupro-nickel alloy.
American silver coins typically contained 90% silver.
Sterling Silver is a standard alloy of a minimum of 92.5% silver - and sterling silver is typically (although not always) alloyed with copper. Metal purity is often quoted in three-figure terms - so Sterling Silver is also known as "925". A full list of common purities of precious metals can be found here
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The origin of the term "Troy" as applied to Troy weights, is believed to be that it was a system of weights used at the ancient fair of Troyes, in Champaign, France. The Oxford English Dictionary states that this fact is not certain - although from other evidence it looks extremely likely. The term does not appear to be a reference to the Troy of ancient Greece.
The Troyes fair is believed to date back at least to the 5th century - and was known to have grown internationally famous by the 12th and 13th centuries, at which time Troyes was a very important center of civilization - and one of the most significant markets (and therefore centers of commerce) in existence. With merchants from many different countries attending the fair of Troyes, it would have been necessary to have a good, standardized system of weights. OED does not mention (although it is mentioned in "The English Cyclopaedia" (1868) by Charles Knight) that other French cities had their own weight systems; such as the pound of Cologne and the pound of Toulouse.
Adam Smith, in "An Inquiry into the Nature and Causes of the Wealth of Nations" (1776) states that in the time of Charlemagne (8th Century), the fair of Troyes was internationally famous and the French livre (French for "pound") contained a Troyes pound of silver. It is also interesting to note that the Roman pound was divided into twelve equal ounces of (approx) 27.264g. Perhaps our units of weight have even more ancient origins...
Furthermore, given that the monarchy of England at the time stemmed from the lineage of Norman Kings, it does seem all the more likely that the Troy ounces system derives from Old France: King Henry II of England, who was born in Le Mans, France in 1133 and was King Of England from 1154-1189, introduced the "pre-decimal" (as it is now called) system of coinage to England, and the "Sterling Silver" standard of 92.5% silver coins - to replace the use of fine silver. According to C. E. Challis' A New History of the Royal Mint (p.89), Henry increased the weight of the English penny in 1158 - and this was done in order to standardize the system with the French Troyes system.
In this system, as with more ancient systems, silver weight and monetary value were tied together: One pound of money contained exactly one Troy Pound of silver. A pound contained 20 shillings or 240 pennies - and the silver pennies contained one pennyweight - or 1/240 of a Troy Pound - of silver. It makes absolute sense that the standard of the fair of Troyes became the standard dictated by an English King born in France and who had substantial French holdings. (We also forget, with our modern systems of paper and electronic money, that in old times money was a commodity measured by weight and derived entirely from the weight of real goods.)
Oxford English Dictionary cites references to the term Troy Ounce in literature dating back to the year 1390. OED mentions furthermore that the Troy Ounce / Troy Pound was also used to weigh bread. Dictionary.com mentions that Troy weights were used to weigh grain - and this makes sense as the original grains as a unit weight were derived from the weight of actual grains of cereal crops! The old system is not entirely obsolete - while researching this article I found grain products for sale online weighed in Troy Ounces - though whether this is through revival or survival of the old Troy system, I know not.
The term "Avoirdupois" comes from Old French meaning "goods of weight" - and according to Russ Rowlett seems to derive from around 1300 when it replaced the "Mercantile Pound" of 15 Troy Ounces. According to Rowlett, the Avoirdupois weights derived from an Italian system of the late 13th century.
Troy Pounds and Ounces were also used by Apothecaries to weigh medicines - only Apothecaries used different subdivisions of the ounce (scruples and drams) and so the Aopthecaries' weights were considered to be their own system.
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Discrepancies between various systems of weight have been an ongoing problem for hundreds if not thousands of years and must have been a cause of interminable confusion and quarrel throughout history. In 1631 Braithwait wrote "A trite discourse of weights and measures: most ponderously dividing them into trois and averdepois." (source - Oxford English Dictionary).
I am curious as to whether the following fact, not mentioned in any of the sources listed below, might be the origin of the difference between the two weights of Troy and Avoirdupois: A coin which is 92.5% silver and has a weight of one Troy Ounce, would need to contain 28.77071604 grams of actual silver - very close to an Avoirdupois "goods of weight" Ounce. This theory is pure speculation - but it strikes me as possible that a Troy Ounce of Sterling Silver once contained "goods (i.e. silver) of weight" of one Avoirdupois Ounce.
There are those who oppose changes in monetary systems and systems of measurement; and while old systems are undoubtedly much more convenient to those who have used them for a long time, systems of measurement eventually change to reflect the commodities and units of actual wealth of the day. Gold is to some extent obsolete as a measure of wealth - as its "usefulness" as a commodity is less than that of past times: In old days a unit of wealth was required that was uncommon and not perishable. Precious metals were therefore the obvious choice. Nowadays, gold's value is largely dependent on its symbolic nature as an item of wealth. However it is easy to understand the attachment to gold as a measure of wealth in comparison to the abstract wealth of pure numbers that we now have.
The Troy Ounce is worth remembering and preserving - as both a royal symbol of standards of purity and quality, and as part of our ancient heritage.
AN
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http://en.wikipedia.org/wiki/Ounce
http://www.metrum.org/measures/index.htm (Stecchini's History of Measures)
http://en.wikipedia.org/wiki/Troy_weight
(Longer) Oxford English Dictionary
http://home.clara.net/brianp/weights.html
Coincraft's "Standard Catalogue of English and UK coins 1066 to date"
http://www.cyberussr.com/hcunn/gold-bri.html
http://vieuxtroyes.free.fr/t/engfoires.htm
http://en.wikipedia.org/wiki/Krugerrand
http://www.royalmint.com/Corporate/AboutUs/History/Toweroflondon.aspx
http://en.wikipedia.org/wiki/British_sovereign_coin
http://www.reference.com/search?q=troy%20weight
http://www.goldsovereigns.co.uk/technicalspecs.html
http://us.geocities.com/tdl.geo/troyes.html
A New History of the Royal Mint By C. E. Challis
http://en.wikipedia.org/wiki/Ancient_Roman_units_of_measurement
http://en.wikipedia.org/wiki/British_coinage#Pre-decimal_system
http://www.unc.edu/~rowlett/units/custom.html
The English Cyclopaedia by Charles Knight, 1868
Le Moyen Age by Gustave Carre
Ounce or Troy Ounce buyer needs to Know! by aesdavid
An Inquiry into the Nature and Causes of the Wealth of Nations by Adam Smith (1776)
Historical Essays in Connexion with the Land, the Church, &c. by Eben William Robertson (1852) p.60&f
The Story of Us Humans, from Atoms to Today's Civilization by Robert Dalling (2006) (p.330-331)
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