HOW ARE COINS AND MEDALS PRODUCED?

Graphic design

The production of a coin or medal is preceded by graphic design. Graphic designs are generally prepared by sculptors or medal designers, usually in A4 format, enlarged compared to original size. In the graphic design, designers also indicate their ideas for the surface finishings of the piece to be produced, such as brilliant, matte, and other surface features.

Preparation of a plaster model

Plaster models are also carved with larger dimensions, with diameters up to 240 – 300 mm, depicting the image of the piece. In contrast to the graphic design in 2D with relief features possibly indicated by shadowing, with the plaster models the designers add the third dimension in the form of relief. (image)

Die production

The Mint’s work begins after completion of the plaster model. The first step is the production of the dies. The approved plaster model is placed in a 3D scanner, which uses a laser to copy the surface and save all the details in a computer file. Using software, the Mint’s programmers can also modify and correct the images, but this only occurs in the interests of production aspects and does not alter the artistic concept. After the digital version of the image has been finalised, the data are transferred to a CNC milling machine.

CNC engraving

A CNC milling machine engraves the digital design onto a soft steel alloy surface. Each side of the piece is engraved in two phases. In the first phase, most of the unnecessary metal is removed in broad strokes. In the second, smoothing phase, the smallest details of the design are reproduced in the steel surface. This process results in the master hub. Compared to the enlarged image of the plaster model, the milling machine produces a master hub reduced to the size of the piece to be struck, which bears an image identical to the original.

The engraver

The engraver then begins to work on the master hub produced by the CNC milling machine, removing any defects that occurred during machining and enhancing the surface details according to the designs (it is important to emphasise that exceptionally precise work by the engraver is crucial in the production of the dies, both for direct striking and for making master dies).

Production of dies

The engraver then has the master hubs heat treated, which hardens the steel. In a high-pressure “squeezing” process, the pattern from the hardened master hub is then pressed into another steel shaft, which bears the negative (sunken image) of the piece. The negative die obtained as a result of this process is either used as a working die, i.e. directly in the striking equipment, or – in the event that a large number of pieces are to be struck – it is processed further as a so-called master die.
In this case, the hardened steel master die is further refined with fine engraving work, after which a master hub is produced which is suitable for making many working dies. As a whole, this is known as the “hubbing” process and it allows for even millions of coins of the same quality to be manufactured. The master hub is extremely important, especially for the production of circulation coins, as in this case exactly the same coin may have to be produced for many years for circulation purposes. Working dies made directly from the master hub can be used for the production of smaller series.

Thanks to this very complex process of die production, we can start with a design move all the way through to striking a medal or coin.

Striking coins and medals

During striking, the image is struck onto both sides of the prepared metal blanks at once, with one or more strikes. (image)
Circulation coins are struck once with pressure of 100-200 tonnes, commemorative coins are struck three to four time with pressures of 360-600 tonnes and the largest coins and medals (up to a half a kilogramme) are produced with hydraulic presses exerting pressures of 2,500 tonnes.

Inspection and bagging

After striking, the coins or medals are carefully inspected for quality. Depending on the final finishing, they are then placed in clear plastic capsules or may undergo further surface treatments, such as galvanising (with gold or silver) or patina finishing. (image)