| Silver Coins |
An Introduction to American Minted Shipwreck Recovered “Cob” Coins
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Silver treasure coins like these were once the most coveted and widely traded money on earth. Much of the world’s economy depended on an uninterrupted flow of these hand-hewn, individually struck coins pouring from New World mints, across the sea to Europe and beyond. Today, they are popularly known as “cob” coins, and are collected by enthusiasts all over the world. Particularly rare types can be worth up to tens of thousands of dollars each.
The Spanish Dollar
Every coin that came out of every mint in the America’s until the 1700’s was made one at a time, by hand, so each is unique. To make coins in the 16th and 17th centuries, blanks were hand-cut from strips of silver. A heated blank, or planchet, was then sandwiched between double dies, and struck with a hammer. Any metal in excess of the requisite weight was trimmed from the outer edges of the coin until the weight was correct. This resulted in irregularly shaped coins whose insignia were often off-center. The dies themselves were made of steel, with insignia impressed into them by direct engraving or by the sinking (stamping) of multiple die punches, each punch being a component of the coin’s design. Just as when two different artists paint an image using the same model, or pattern, the symbols engraved into the dies reflect the artistic individuality of each engraver.
Coin denominations are counted in reales.
- Eight reales of silver equaled the one-ounce Spanish silver dollar of approximately 27.2 grams—less than the troy ounce standard today.
- Four reales coins, at ½ ounce each, are half the weight and were half the value of the eight reales coin.
- At ¼ ounce, two reales coins are half the weight and were half the value of four reales coins.
- At 1/8 ounce, the one reale coin is half the weight and was half the value of the two reales coin, having 1/8th the value of the eight reales coin.
- ½ and ¼ reale coins were also produced intermittently throughout the Spanish Colonial period, but are exceedingly rare.
The value of money was determined by the purity and weight of the metal. That being the case, it was not uncommon at the time to cut coins into pieces and weigh the pieces to make change—hence the origin of the money’s legendary nickname, “pieces of eight.”
The symbols carved into the coin dies and struck into the coins represent the power of Spain, and when the power changed, the insignia changed as well.
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Cleaning Shipwreck-Recovered Silver Coins
Because of a chemical reaction between the metal and the salt water, a residue of silver called silver sulfide forms, blackening the coins, and fusing them together in the shape of the wooden chests that once held them. Blackened and encrusted silver shipwreck recovered coins are cleaned by a technique called electrolytic reduction—along with lots of elbow grease. First, coins are separated from the conglomeration, and then suspended individually from metal alligator clips into a tub of soda ash and water. The alligator clips are secured to rods with stainless steel wire, and the rods are wired to a battery, with voltage and amperage determined by the number of coins in each batch. Next, the power supply is engaged, beginning a process of reverse electrolysis. After cleaning, each coin is studied, photographed, documented, graded, and certified.
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Excerpted in part from Treasure Coins of the Nuestra Senora de Atocha and the Santa Margarita, by Carol Tedesco, published by SeaStory Press, Key West, Florida, USA, and may not be reproduced in print or electronically, in whole or in part, without express permission of the publisher and author.
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