PROOF COINS - The Quest for Perfection
The modern process of minting of proof coins of pristine quality truly epitomises this ancient art. The process from initial drawing to completed proof coin is a protracted one involving several hundred hours of work.
The DesignThe first step is to produce a drawing of the proposed design. The artist needs to master two special techniques - the ability to create a design which works within a circular framework and which may be translated effectively into a coin many times smaller than the original drawing.
The Steel Tool
The Master ToolIn a process known as hobbing, an hydraulic press, exerting many tonnes of pressure, is used to press the reduction punch several times into the cone-shaped end of a prepared steel billet. Several pressings, interspersed with machining and softening, may be necessary.
The Proof DieIt is generally accepted that a proof coin has the design 'frosted' and the table area highly polished. To achieve this, the die has to undergo special preparations. First the table area of the die is given a light polish and the face of the die is covered with transparent adhesive tape. Using a surgical knife blade, the tape covering the design is carefully cut away. The exposed design is then sandblasted using a fine grade grit to give the frosted effect.
The remainder of the tape is removed and the table area of the die is polished, using various grades of wooden 'lapping' sticks and diamond paste, until it has a mirror-like finish. To protect the surface, the face of the die is then hard chrome plated to a depth of 3-4 microns.
The Proof BlankThe surfaces of the blanks to be used for proof coins are specially prepared, in a buffing process, to produce a mirror-like finish. To ensure that the blanks going forward for coining are within the weight tolerance allowed by legislation, each blank is individually weighed in a computer-controlled balance.
Great care is taken throughout the procedure to ensure that blanks are not damaged in any way. During the cleaning and weighing of the blanks, tongs with specially protected jaws are used. Thereafter, operators only handle the blanks and coins by gripping the edge while wearing finger cots and gloves.
Minting the Proof CoinsThe press is set up with a reverse die and an obverse die in the top and bottom die holders and a collar with a serrated bore manufactured to give the correct number and configuration of mills (serrations) around the edge of the coins.