MAYER MINT GMBH GERMANY

Making Coins

Minting techniques have traditionally been highly precise and guarded functions commissioned and governed by a country’s reigning authorities and a few hand selected mints in the world.

From the outset, minting techniques consisted of two main areas of work – the production of suitable blanks of a defined composition and exact weight; and the production of the tools for striking the coins. Principally, nothing has changed in this regard from the earliest minting techniques till today. Only the methods have improved with industrialisation and technical progress.

The Genesis of Coins; a Historical Approach

It is believed that the first coins were struck during the 7th century BC by the Lydians in Asia Minor. These were made from coin blanks of a consistent composition of gold/silver alloy called electrum. For this purpose, molten electrum was poured into suitable forms. They started with simple moulds and later moved to more complicated moulds which made possible the production of a larger number of coins at one time.
For many centuries, this kind of production of round coin blanks remained basically unaltered until the growing economy in Europe during the 16th century saw a dramatic increase in the demand for coins. Minting techniques were therefore modernised to produce coins of a more consistent quality and in greater quantities.
From small hand driven presses, the development passed via falling hammer presses and water driven hammer works to complex spindle presses. As early as 1600, Nicolo Grosso used a spindle press in Florence, with which he punched coin blanks from rolled sheets of precious metals. This technique is still in use today, albeit with high capacity punching presses which produce large numbers of blanks with one stroke with vastly improved accuracy.

Even from the earliest times, coins were struck with two coining dies – a lower die depicting the coin in a negative form, and a similar upper die. The coin blank was then placed between these two dies and the upper die struck with a heavy hammer, thus rendering a positive image on the blank. The hammer method was used long into the Middle Ages. Even now, we occasionally speak of coins being struck.

The start of the Industrial Age (late 18th – early 19th century) brought a plethora of various minting machinery which culminated with Diedrich Uhlhorn inventing the “toggle press”. The principle of the “toggle press”, which allows several hundred circulation coins to be produced per minute, lives on in today’s modern mechanical mints.

Modern Minting Techniques

Today, coins are manufactured under extremely strict control and tight security at every stage of production. Production is carried out under constant surveillance with quality checks conducted at all stages to ensure accountability, and to minimise loss.

The modern minting technique starts with the design process. Once the design is finalised, dies or moulds to accommodate the design are prepared. The selected design is then transferred onto a plaster mould made up to five times the size of the actual coin. This painstaking task takes about three weeks to complete. The design on the plaster is then transferred onto a rubber resin mould which is later used to make an epoxy resin mould.

Next, this epoxy mould is mounted onto a reducing machine called a pantograph which traces the exact contour of the mould onto an engraved master die bearing the same diameter as the coin to be struck. From this master die, another working master die or master punch is made using a matrix die.

The master punch is used to produce a number of working dies which are the actual dies used to strike the coins. The tremendous pressure applied to strike a coin means that the working die will wear off after a certain number of strikes. As a result, they have to be replaced by new dies before more coins are struck. Thus the number of these working dies required depends on the mintage of the coins. Two sets of dies are needed to strike a coin – one for the obverse, the other for the reverse of the coin.

The final and actual minting stage is the transfer of the design to the metal coin blanks. In making such blanks, bars of the required metal are scrubbed to create a consistent surface, free from impurities or imperfections which not only produce defective coins, but also reduce the life span of the dies. The bars are later annealed and rolled into strips of the exact thickness required for each denomination of coin.

The strips are now ready for the next process - the cutting of disc–shaped blanks or planchets. These blanks are passed over a sorting screen to weed out incomplete and defective blanks. Rejected blanks and remaining parts of the metal strips are returned to the furnaces to be remelted into bars. Good blanks are cleaned, rimmed into the required sizes and annealed again to a coinable hardness so that they can be stuck to capture the full relief of the designs of the working dies.

Proof blanks are manually fed by hand into automatic presses which can strike almost 100 commemorative coins per hour. The high quality required for proof coins does not allow any mass production.

Coin presses consist of two important components – one working die for the obverse and another for the reverse, and a collar. The collar forms the wall of the coining chamber which provides the impression for the uniform circular outline around the coin. As its name implies, the collar prevents the striking pressure from spreading onto the flange. Apart from preventing imperfect strikes, the impression on the coin’s edge (either as a recess or raised inscription) deters forgery or clipping (an illegal paring of metal from the circumference of the coin).

After the coins have been struck, they go through a final manual inspection by trained quality controllers to check for flaws. Upon acceptance, commemorative numismatic coins are normally sealed in capsules and placed in presentation boxes. Finally, they are placed in cartons or boxes, weighed and sealed before delivery.