How Are Coins Made?

1.  Remove the metal from the earth

2.  Move the metal to the Mint

3.  Mint the Coin

[None of this proves especially easy...]

Why do coins vary in appearance, even when made the same year by the same mint?

Coins start as blank pieces of metal called "planchets".  These planchets are then struck by dies, metal objects with incuse design, to produce a coin.

The mint produces a master hub is used to make master dies, master dies are used to make working hubs, working hubs are used to make working dies, which in turn are used to strike the coins.  This “hubbing” or "hobbing" process requires that the die stock be annealed between each impression and varies greatly for each series. For example, in the dollar series, Morgan Dollars (1878-1904) had hubbing performed 7-10 times whereas for Peace Dollars (1921-1935) it was done 3-5 times.  That is why Peace dollars look soft or mushy compared to Morgans, their details/devices were simply not struck as sharply.

The master hub, which produced the first master die, which produced the first working hub, which made the first working die, which  struck the first coins on the best planchet produced the highest quality coins. he mint typically used a working hub to produce 250 working dies. Now, depending on the standards set by each mint (they did vary, especially in the early part of the 19th century), the number of coins in the production run, and the number of available working  dies, the average number of coins struck by each die would vary from between 125,000 to 250,000 coins. Each time the hub produced another die some metal wore off so the next die lost some detail.  Therefore every coin struck by that die would increasingly lose even more detail as the die wore down. TThe first hubs and the first dies from each hub produced the best example of every coin design.  Defects in dies or planchets can produce varying quality coins. Polishing of all or part of a die also effects the outcome of the coins struck. This explains the difference in strike on coins.

Mint production standard were driven by numerous factors such as the underlying social conditions of each year, the availability of materials and men, the chief engraver, designer and minter and political or economic parameters.  The US has had eight different production mints over the years. Two mints were used to produce early gold issues. One mint has only been used to produce proof coins. Five mints produced larger silver coins that have provided much of the interest amongst the coin collecting fraternity.  Each of these mints set their own standards and quality assurance/control methods for coin production. 

Now, it takes extreme of pressure to strike a coin.  The pressure actually turns the planchet into molten metal which flows through the devices (nooks and crannies) of the hub to produce the coins surface (design/devices). This pressure, in turn, puts much wear and tear on the dies.  To prolong the life of the dies some mints used less striking pressure, varying from 50 tons per square inch (!) up 150 tons per square inch depending upon a myriad of production concerns. The less pressure used, the more soft or mushy the coin appears.

How were proof-like coins produced?

Many conditions and factors must simultaneously come together her to produce a proof-like (PL) coin.  Higher quality coins with better 'strikes' (the clarity of the coin devices [details]) demand a premium from collectors.  Those with a watery mirror like fields and finish (known as proof-like [PL], Deep Mirror proof-like [DMPL], or Cameo - the best) demand even higher premiums as they are the finest coins produced by the mint using standard minting techniques.  Since DMPL and PL coins are the first few coins struck from new dies, they have the best strike, relief, and their details are truest to the mints original design. Their fine detailing and fields result from the use of brand new dies and planchets.

TERMS

Annealing drum>upsetting mill

Milk Spots - These are distracting hazy areas on proof coins.  In Q. David Bowers' book, Silver Dollar Encyclopedia, he provides an explanation from one Wayne Miller detailing what might be the most reasonable explanation for 'milk spots'.  Namely: "The planchets were improperly washed and dried after they had emerged from the annealing ovens and subsequent acid bath. Also, an increase in the concentration of sulfuric acid and water solution used during this cleaning and polishing operation could have lightly etched the surface of the planchet in some places."

Basining - A step in the coin minting process where the die surfaces are set against a rotating zinc plate; polishing of the die. This process helps the coin properly strike.

Lamination -   Laminations can occur are always possible when dealing with metal of any kind that has been melted.   Lamination is predominantly a planchet problem where gas bubbles or other impurities in the melted metal are trapped in the molten planchet and then cool.  They are then either elongated or smeared during the rolling process.  Because of this the metal above the bubble is not attached to the metal below.  When this rolled bubble breaks, like a squeezed zit, a damaged planchet results and surface flaking starts ('lamination peel'). 

Coin Errors

Explanation of Various Coin Errors

http://geocities.com/researchtriangle/facility/4968/educational1.html

Further Resources

Cooper, Denis R.  THE ART AND CRAFT OF COIN MAKING: A HISTORY OF MINTING TECHNOLOGY.  London: Spink, 1988.