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By their very nature, coins are highly
durable, convenient, mobile and accurate modes of
payment and investments. Commemorative coins are
struck from precious metals, i.e. Platinum, Gold,
Silver, and their alloys, and non precious metals
i.e. Copper, Nickel. To be legal tender, all commemorative
coins must possess the following essential properties:
The precious metal of every commemorative
coin must be accurate.
Commemorative coins must be precisely weighed
and their monetary value guaranteed by the issuing
authority (usually the ruling monarchy or government).
The issue must be limited. The smaller the
worldwide mintage the rarer the coin, and in consequence
the potential to increase in value.
In accordance with these demands, 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.
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The Genesis of Coins; A Historical Approach
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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. Later, there was a transition to
more complicated moulds which made the production
of a larger number at any one time possible.
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 demand
for coins. Minting techniques therefore were industrialised
to meet this demand.
From small hand driven presses, the development
passed via falling hammer presses and water driven
hammer works to 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. The permanent refinement of analysis
and measuring techniques, the accuracy of weight
and alloy composition were vastly improved.
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Even from the earliest times, coins were struck with 2
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 a long
way 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
when Diedrich Uhlhorn invented 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
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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 minimise
loss. The modern minting technique is marked
by a high degree of mechanical and aesthetic excellence.
This entails a logical sequence of clearly defined
procedures beginning with coin design –
an art in itself.
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The design is made by an artisit, by means of a pencil
sketch. Photographs or similar descriptive material as
well as personal ideas of the artist serve as pattern.
If the design comes up to the demands and expectations
of the customer, the plaster mould can be made.
Once the design is determined, dies or moulds to accommodate
the design are prepared. The selected design in all its
details are transferred onto a plaster mould made up to
five times the size of the actual coin. This painstaking
task takes about 3 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. The
reason for first engraving the design on plaster is because
plaster gives a better finish than other materials used.
Also, any errors made can be corrected at this stage with
plaster. This is impossible on rubber resin or epoxy.
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.
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| 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. 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. |
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The final and actual minting stage is the transfer
of the design to the metal coin blanks to be struck.
Coin blanks used for striking commemorative coins can
be purchased from coin blank suppliers, or be produced
by the mint itself.
In making such blanks, bars are first scrubbed to provide
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 to become strips of metal having the exact
thickness specified of 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.
As in days of yore, modern 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 inspection to check for flaws. This is done manually
by trained quality controllers. After inspection and
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.
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