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Virtual coin challenge - double struck colonial portrait 8 Reales

TwoKopeikiTwoKopeiki Posts: 9,714 ✭✭✭✭✭
edited January 26, 2021 6:02AM in World & Ancient Coins Forum

I mentioned on another thread that I see these fairly often and toyed with an idea of assembling a complete date run (no major varieties) for Mexico Mint but never had the energy or the funds to do it, so i'd like to do it digitally as I come across examples in my search. Note: unless specifically stated, none of these coins belong to me.

The first few responses will be populated by corresponding monarchs and mints.

I welcome anyone with examples to post them and I will add them to the corresponding section.

To understand why double-striking (and die clashing, for that matter) happened with relatively high frequency, we must start with the machinery. Portrait 8 Reales of the late 18th - early 19th Century were struck on a flywheel press, a type of screw press, without a collar, after the blanks have been edged in a parallel edging die.

Usually took 3 or more men to operate: 2 "spinners" and 1 "moneyer". The latter would be seated and would insert planchets and remove the finished coins. The "spinners" would tug on leather straps attached to the iron bar. The bar was attached to a heavy iron screw which drove an upper die down towards a lower one when the men on one side of the bar pulled it towards them. Then, when the men on the other side tugged on the bar, the screw and upper die were raised and the seated man would remove the finished coin.

Here's an illustration that's probably familiar to quite a few:

A large screw press had two horizontal arms (labeled "D" in the woodcut below) attached to the vertical screw. As the arms were rotated horizontally the screw (labeled "I"), with a die ("N") at one end, moved up or down. The amount of force varied with the kinetic energy of the arms. Faster moving arms meant that force was applied to the die within a shorter amount of time; heavier arms carried more energy for the same speed of rotation.

Press arms were often tapered, and this allowed weights ("F") to be added and positioned on each arm to produce the desired amount of force. Heavier weights could also be used to change the total force applied to a die. Weights were commonly held in place with a cotter pin or similar locking arrangement. The arms were moved by a workman at each end "throwing" the leather straps ("slings" labeled "G") and then catching the rebounding arm to start another cycle.

According to various Mint records of the period, a good team of coiners could turn out several dozen coins per minute, or 1 every 2-3 seconds. Once the hammer die started the downward descent, there wasn't much that could stop it. If the moneyer was not fast enough to replace the struck coin with a new blank, the coin would receive another strike or, if the previously struck coin cleared-off the anvil die, the dies would clash. Remember, there was no collar to hold the planchet in place.

One of the cool design features was the square shape of the iron driving rod that moved up and down with the hammer die mounted at its base. The square shape mitigated the rotational force from the screw action that would have otherwise torqued the hammer die and caused uneven striking. There was often little to no "play" and if the already struck coin remained seated on the anvil die and received another striking, the doubling in a lot of cases would be only a few millimetres.

As you can imagine, since the coin continues to rest on the bottom die during the second strike, there rarely any doubling observed on the reverse. If anything, the reverse ends-up nicely struck in a lot of cases.

Since there was very little wobbling of the hammer die due to the square driving rod, some doubling posted below will be very slight. If you don't see it right away, just right-click the image -> open in a new tab / window for closer inspection. I will try to find and upload higher resolution shots.

[more to come]


8 Reales Madness Collection

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