How to Read a Cob

Mint marks, assayers, the shield and the cross — and why most cobs carry no date. A field method for attributing hand-struck Spanish colonial silver.

A cob is read in seven passes: fabric and weight, design era, mintmark, assayer initial, date bracket, rarity, and — only last — the wreck window. The shield side gives you the crown, the arms and usually the mint and assayer; the cross side gives you the era and often the only legible date; and roughly most cobs never carried a readable date at all, which is why mint and assayer do the work.

What is a cob, exactly?

Cob is the English shorthand for the Spanish macuquina: hand-struck colonial coinage cut from silver bars and struck between hand-cut dies, produced in the Americas from the 1570s until milled coinage displaced it in the mid-18th century. The name comes from cabo de barra, “end of the bar.”

Cobs were money by weight and fineness, not by beauty. Flans were clipped to the correct weight, struck once, and shipped. That is why almost every cob is irregular, off-centre and only partly legible — and why attribution is a skill rather than a lookup.

Pass 1 — What do fabric and weight tell you?

Start with the physical coin. Weigh it to 0.01 g and compare to the standard: about 27.47 g for an 8 reales, 13.7 g for a 4, 6.9 g for a 2, 3.4 g for a 1, all at .9305 fine in the hammered era. Look at the edge: hand-cut, uneven, sometimes showing the bar's cut faces. A perfectly round, uniformly thick “cob” is a warning, not a bargain.

Pass 2 — Which side is which, and what is on them?

Pass 3 — Where is the mintmark, and what do the letters mean?

Pass 4 — Who was the assayer, and why does one letter matter so much?

The assayer was the official who certified the silver's fineness, and his initial appears beside the mintmark. That initial is the single most powerful attribution tool on an undated cob, because assayer terms are documented year ranges. Read the letter and you have bracketed the coin to a period of a few years without ever seeing a date.

This is also why the assayer initial is worth faking. On a genuine coin the letter is struck in the same relief and style as the surrounding devices. Re-engraved letters look sharper than everything around them, sit at the wrong angle, or cut through toning.

Mint plus assayer plus design era usually gets you within a few years. Chasing a date first is the beginner's mistake.

Pass 5 — Why do so few cobs show a date?

The date sat in the outer legend, which is precisely the part that falls off the flan when a coin is struck off-centre on a clipped planchet — and precisely the part that erodes first after centuries in salt water. The result is that fully dated cobs are a minority of survivors, and a legible date is a price event rather than a detail.

Our August 2026 auction study measured it directly: dated Potosí 8 reales cobs with legible assayer initials realised roughly $2,684 to $4,636, while undated examples of the same design clustered far below. When you see “dated” in a description, treat it as a value claim to verify under magnification, not a throwaway.

Pass 6 — How do you judge rarity without a catalogue in hand?

Pass 7 — Only now, does the wreck window fit?

The last step is to test the wreck claim against what you just read off the coin. A wreck can only carry coins struck before it sailed, from mints that fed its fleet. Potosí silver rode the Tierra Firme galleons out of Cartagena and Portobelo; Mexico City silver rode the New Spain flota out of Veracruz. A Mexico-mint cob on a Peruvian Pacific capitana needs an explanation.

If the date on the coin is later than the wreck, the attribution is finished — no discussion. If mint and fleet do not correspond, ask for the salvage documentation before anything else.

Attribution runs coin-first, wreck-last. Read the metal, then the design, then the letters, then the paperwork.

Frequently asked questions

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