When you look at Mexican cobs of the 1600s and 1700s, you may wonder how cob planchets were made, given their sometimes crazy shapes. We know from contemporary documents that an innovation at the end of the 1500s—in effect the invention of cobs—greatly sped up the coining process, specifically the planchet preparation… but how? A logical starting place is the popular phrase cabo de barra (“end of the bar”), which some experts think is the origin of the word “cob,” pronounced exactly the same as the first syllable of the word cabo. Interestingly, older Spanish numismatic dictionaries specify cabo de barra as the end-pieces (the oddest shapes) from the Mexican mint.* But this makes no sense if the planchets were cross-cut slices of thick, salami-like ingots or big rectangular loaves like the bullion bars we see from shipwrecks. Instead you have to think of the “bar” as a flat, horizontal “strap,” something the Spanish colonial mint workers referred to as a riel (akin to the word “rail,” as in railroad).**

 So what did a riel look like? Until recently we did not know of any surviving examples; but in our Treasure Auction #6 we noticed something interesting in lot #1972, which included a 1960s photo of a display in the Real Eight Company’s museum in Satellite Beach, Florida, with the label HOW “COB” COINS WERE MADE (see photo below, taken out of focus through the glass display). In the display were several Mexican cob 8 reales (recovered by Real Eight from the 1715 Fleet) lined up so their straight edges met.  Evidently eight of these coins together made a flat, 1” to 2” wide ingot with undulating sides: a silver strap! At the top of the same display was an uncut strap of silver. Was it an original riel, salvaged from one of the wrecks? A quick call to original Real Eight member Lou Ullian confirmed that “strap” was the real deal, although its current whereabouts are unknown, and that it was rough on the bottom and smooth on the top, just as you would expect if the silver was simply poured onto a flat surface and left to spread out and cool naturally. In retrospect it is hard to believe that such a numismatically significant artifact received little or no attention, but at that time crude cobs and how they were made were of little interest to serious coin collectors.

The rest of the story is no mystery (see second footnote). The planchet-preparer at the mint measured out 216 grams (8 x 27) of molten silver at the proper fineness and temperature (not too hot or it would make a flat pool) and poured it into a snake-like line, which flattened out naturally as it cooled. Next, he found the centerpoint of the strap by balancing it, and then he cut perpendicularly at the center of balance, creating two halves of equal weight, to each of which he applied the same principle two more times to arrive at eight coins of more or less equal weight. If he overcut or undercut by a little bit, so be it—it had to average out to 27 grams per coin since the total weight of the strap was proper for eight coins. To make straps for smaller denominations, the temperature of the silver would be adjusted higher for thinner straps and therefore thinner coins (and of course less weight to start with).

 What happened next explains the sloping sides and blunted points that we see on Mexican cobs. Unlike natural sides from a strap, cut sides on each coin caused them to harden faster and crack, unless they were hammered down, also making those edges less sharp. A similar principle was applied to the all-too-common points left by the shears at the ends of a cut. Sharp edges and points, after all, could be dangerous to handle and impossible to bag and transport in quantity. It was an expedient method, albeit without regard to aesthetics.

 The coins we see today are clearly examples of these methods. Not only do these cobs have random shapes with just one or two straight, cut, hammered-down sides, they also come in varying weights around a more or less proper average of 27 grams to the 8 reales. Furthermore, some specimens demonstrate very strange shapes (particularly what we can assume to be the end pieces) and even have “bubble holes” that are simply where the cooling silver in the ingot hit a snag and flowed around an air pocket.

 We must emphasize that this method only applies to Mexican cobs from the early 1600s to early 1700s. The earlier coins and those from other mints are much more round, which means either there was a different method for making those blanks or the blanks were simply (but laboriously) trimmed down to more circular shapes. And we are not counting “Royals” and “Hearts” and other intentional shapes, which were specially prepared by hand and not subject to batch preparation.

 Next time you see odd-shaped Mexican cobs, take a closer look at the edges and consider how they were cut from straps, and then perhaps their shapes will not seem so strange after all.

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* See Diccionario de la lengua castellana by Melchor Manuel Nuñez de Taboada (Paris, 1822) and Diccionario enciclopédico-mejicano del idioma española, Volume 1, by Emiliano Busto (Mexico City, 1883), and note that the second book alternately refers to cabo de barra as the last and presumably short payment against a debt.

**See Arte de ensayar oro, y plata, con breves reglas para la theorica, y la practica, en el qual se explica tambien el oficio de ensayador, y mareador mayor de los reynos; el de los fieles contrastes de oro, y plata; el de los marcadores de plata, y tocadores de oro; y el de los contrastes amotacenes, segun las leyes de estos reynos by Bernardo Muñoz de Amador (Madrid, 1755), which mentions using a compass to mark cut points on the riel, along with complicated mathematical formulas.  Also illuminating is Breve relacion del ensaye de plata y oro by Mexican mint assayer Geronymo Bezerra (Mexico City, 1671, available in a 2004 digital edition by Biblioteca Virtual Miguel de Cervantes). Rieles were also made in gold: Records for the Bogotá, Colombia, mint state that an amount of “oro en rieles” was brought to the mint by the merchant Martín de Verganzo y Gamboa for making gold cobs in 1627

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