Latin Monetary Union: coins, silver, and gold

What was the Latin Monetary Union?

The Latin Monetary Union, often shortened to LMU, was not a single currency. It was a treaty that made several national coinages interchangeable by fixing weight, fineness, and diameter. The convention of Paris, signed on 23 December 1865, set the terms: a common silver unit of 5 grams at 900 thousandths, a gold unit of 6.45161 grams at 900 thousandths, and a bimetallic ratio of 15.5 to 1 between the two metals. Member states agreed to accept each other's coins at face value, which meant a French 5 franc piece could circulate in Belgium or Italy without being weighed at every counter.

How do you identify a Latin Monetary Union coin?

Start with the metal, the weight, and the fineness, because those are the numbers the treaty fixed. A silver 5 franc coin of the union type weighs 25 grams at 900 thousandths. A gold 20 franc coin weighs 6.45161 grams at 900 thousandths. Those two figures are the backbone of the series, and a coin that does not match them is either a different denomination, a later issue outside the union standard, or something else entirely.

What did the 15.5 to 1 ratio actually do?

The ratio of 15.5 to 1 was the exchange rate between silver and gold inside the union. It said that 15.5 units of silver by weight were worth one unit of gold by weight. In practice, it fixed how much metal went into each coin and made the two metals legally linked at that rate.

What was the Latin Monetary Union?

The Latin Monetary Union was a currency agreement signed in Paris on 23 December 1865 by France, Belgium, Italy, and Switzerland, later joined by Greece and others. It fixed shared standards for silver and gold coins, including a gold-to-silver ratio of 15.5 to 1, and it stayed on the books until its formal dissolution on 1 January 1927. For a collector, the union matters because its rules left a large, well documented body of coins, from the 5 franc silver piece to the 20 franc gold piece, that can still be identified, graded, and compared today.

The system was never static. Silver prices moved, smaller silver coins were debased in some states, and the union's rules were revised more than once. The full arc, from the 1865 convention through the later amendments to the dissolution on 1 January 1927, is set out in the chronology on Latin Monetary Union history, which treats the period as a single connected story rather than a set of national anecdotes. That framing is useful for a reader who has met LMU coins in a dealer's tray and wants to know why the same design logic appears across several countries.

How do you identify a Latin Monetary Union coin?

Next, read the mint letter. French coins of the period carry a small letter that identifies the workshop: A for Paris, and other letters for branch mints. The letter is part of the coin's identity, not a decoration, and it changes the population of surviving pieces. Then look at the different, the small privy marks and engraver's symbols that changed over time. A single date can exist with more than one combination of mint letter and different, and collectors treat those combinations as separate entries.

Edge lettering, diameter, and the orientation of the dies also help. None of this requires laboratory equipment. A decent scale reading to 0.01 grams, a caliper, and a reference list of mint letters will separate most genuine union coins from the rest. The remaining cases, where weight and diameter agree but something feels wrong, are the ones that go to a specialist.

What did the 15.5 to 1 ratio actually do?

A fixed ratio only holds while market prices stay close to it. When the market price of silver fell relative to gold, silver coins became worth less as metal than as money, and people tended to keep or export the gold. When the market moved the other way, the opposite happened. This is the classic bimetallic problem, and the union lived with it for decades. Member states responded with limits on silver coinage, changes to legal tender rules, and eventually the suspension of free silver coinage. The 15.5 figure is therefore not a footnote. It is the mechanism that explains why the union was revised, why some issues are common and others are not, and why the series ends when it does.

Which coins does a beginner meet first?

Two denominations dominate the entry level. The 5 franc silver coin, 25 grams at 900 thousandths, is large, common in circulated grades, and carries the portrait or emblem of its issuing state. The 20 franc gold coin, 6.45161 grams at 900 thousandths, is smaller than many people expect and is the piece usually called a Napoleon when it is French. Both were struck in several countries under the union standard, so a beginner can compare the same weight and fineness across different national designs.

Condition is the next thing to learn. The French grading scale runs from FDC, fleur de coin, meaning essentially as struck, down to usée, meaning heavily worn. Between those extremes sit the intermediate grades that most surviving coins occupy. A circulated 5 franc piece and an uncirculated one can differ by a wide margin in price, and the difference is judged on surface, relief, and the presence of original luster, not on age alone.

Pricing follows a method rather than a single number. Dealers and auction houses quote ranges that depend on grade, mint letter, different, and the number of pieces known. Auction results are the most visible reference, but they need to be read with the buyer's premium and the date of sale in mind. A price from ten years ago is a historical data point, not a current quote.

How should a new collector store and handle these coins?

Handling comes first. Hold a coin by the edge, over a soft surface, and keep bare fingers off the fields. Skin oils leave marks that are difficult to remove without affecting the surface, and any cleaning that removes metal or luster reduces the coin permanently. If a coin needs to be examined closely, cotton gloves and a clean, well lit table are enough.

Storage is a matter of isolation and stability. Individual holders, whether paper envelopes, cardboard flips with inert plastic windows, or hard plastic capsules, keep coins from rubbing against each other. A dry place with steady temperature limits the conditions that encourage tarnish and corrosion. Silver and gold react differently to their surroundings, so a mixed tray is a poor default. Labels matter too: record the denomination, date, mint letter, and different at the time of acquisition, because those details are easy to forget and hard to reconstruct later.

Starting a collection does not require a large budget. A reasonable path is to pick one denomination, one country, or one date range, and to learn it thoroughly before widening. The union series rewards that approach because its rules are documented and its coins are numerous. A collector who knows the weights, the fineness, and the mint letters can evaluate an offer without relying on the seller's description.

What remains uncertain about the union?

Several points stay open in the popular literature. The exact effect of the union on everyday prices in member states is debated, and the surviving evidence is uneven across countries. The treatment of coins from states that joined later, or that left and returned, is not always clean in catalogues. Small silver denominations were debased under rules that varied by state, which makes a simple union-wide fineness figure misleading for anything below the 5 franc piece.