Making a Coin - The Process
Every stage of coin production, from the first rough design to the finished proof or circulating coin, is carried on at the Mint in an atmosphere of the strictest security.
Designing a Coin
- Firstly, this has to be translated into a preliminary drawing in the shape of the eventual coin, together with the lettering value and symbolic elements
- The finished design is sent to the government body for approval
- Any coin which has the Queen's effigy on the obverse also has to be submitted to Her Majesty's Government and ultimately to Buckingham Palace for the Queen's assent
Producing a Plaster
- Once the designs have been approved, artists of the Sculpting Department sculpt large models from which plaster casts are taken
- A positive impression is taken from the master and this is then sent to the Die-cutting department
Cutting a Die
- The image is cut on a hob or master die by a steel cutter working in unison with a stylus which moves slowly over the hardened matrix, rather like the needle of a record player, but from the centre to the outer edge
- This process takes up to 28 hours
- By means of a reducing machine, the design is transferred to a hub in the correct dimensions of the eventual coin
- Completed hubs are examined painstakingly through a high-powered magnifier
- The hobbing stage transfers the image from the hub to the working die
- A negative impression is picked up on the die, using a press applying 400 tonnes pressure per square inch
- After turning and milling, the soft steel die is hardened chemically and physically by heating in a special temperature controlled salt bath for about twelve hours, and then quenched in a special solution
- This gives the die its unique hardness and the durable qualities needed for the high pressures and the intense clarity required in the coining process
- The dies are then ground and polished to a mirror-like finish by hand using ground diamonds
- They are then ready for coining
- The coining metal is supplied in huge coiled strips which are cut into the required shapes by blanking presses under a pressure of 50 tonnes per square inch
- After cutting, the blanks are carefully checked for slivers and crescents of surplus metal, and then passed to the annealing and blanching stage, where they are washed and brought to a brilliant light lustre, suitable for coining
The coins which excite the greatest interest among collectors are those prepared and struck specially in deluxe versions. In bygone times, before coins went into general production, a few strikes were made from the die at the beginning and these were preserved as proof that the dies were correctly engraved. Because greater care was taken to ensure good strikes, these proofs tended to differ from the issued coins in the clarity of the impression.
From this developed the custom of striking proofs from the specially prepared dies, partly for the records and partly for presentation purposes.
Proof Coins - Today
Today proof coins are struck specifically for the collector's market. Special dies, often with the high-relief portions of the design frosted, are used in conjunction with blanks polished to an impeccable mirror finish using diamond paste and swansdown pads.
At the Pobjoy Mint, such coins are each struck four times to achieve the sharpest possible impression, then submitted to a microscopic inspection by highly trained staff to ensure that only examples in superlative condition are encapsulated and boxed, along with their certificates of authenticity, for sale to discerning collectors.
Circulating coins are struck to very high specifications because of the need to pass the stringent tests of vending machines and the need to stack easily. For these reasons their designs tend to be in very low relief. As examples of the actual money in use, they are not without interest to collectors which is why mints usually supply circulating coins as carefully selected specimens in year sets.
Circulating coins are struck on high speed presses. The coins are then check-weighed and examined for flaws and defects. After passing this examination they are counted again and hermetically sealed in bags before final check-weighing again