Modern design and minting

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.

Design and plasters

Initially, 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. Once the design is detitleined and approved, dies or moulds to accommodate the design are prepared. The selected design in all its details are transferred onto a plastilene (modeling wax) model in bas-relief from the approved sketch, which is made up to five times the size of the actual coin. This painstaking task takes about 3 weeks to complete and the sculptor-engravers must keep in mind the depth of relief that is suitable for producing coins. The design on the plaster is then transferred onto a rubber resin mould which is later used to make an epoxy resin mould. Melted rubber is then poured into the 'Plaster of Paris' mould to form the 'Silicone Rubber'. 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. From here onwards, the process of reducing and transforming the design to the actual size onto tool steel begins. It involves running the araldite mould onto the reducing machine, with the design traced on tool steel. This process is called 'reduction punch'. The reduction punch will go through a few cycles untill the master die is formed. From master die, several 'coining dies' will be produced.

Master and coining dies

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. The 'coining dies' is installed onto the minting machines according to the required denomination. Then, blanks are fed onto the 'Feeding Hopper'. Each blank is minted with 100 to 150 tonnes pressure.