Description

A special anniversary edition of the 50p celebrates the science behind the shape and featuring a privy mark.

50 years ago a revolutionary new coin entered circulation ahead of the decimal switchover. Half a century later it’s still a testament to the science behind its radical design. A special anniversary coin pays tribute to Hugh Conway and his team. Tasked with creating a coin easily distinguishable by touch and sight that would still roll smoothly, their perfectly engineered solution gave the world’s first seven-sided coin.

In 1967 the Deputy Master of the Royal Mint approached the Decimal Currency Board to ask for their advice on the introduction of a new coin. The Technical Member (and the only engineer) on the Decimal Currency Board was Hugh Conway. He had found in a mathematical textbook formula for a non-circular shape of constant breadth and asked the design office at Patchway, near Bristol, which normally worked on the engines for aircraft such as Concorde, Vulcan and Harrier to draw out the shape. However, this turned out to be a wavy-edged form with re-entrant sides which would not roll and which could not be measured easily. A designer, Colin Lewis, suggested a much simpler shape which in its basic form is an equilateral triangle with a small circle centred on each apex and with a larger circular arc centred on each apex but tangential to each of the two opposite small circles. A drawing was made to illustrate the proposal which was accepted by Hugh Conway. He chose seven sides as a compromise between too radical a shape, which might not be acceptable to the public, and having too many sides, which would make a shape visually difficult to differentiate from a circle. The shape was drawn out by Dave Brown and samples made from stainless steel by the Model Shop, together with a section of perspex channel with a bend to demonstrate that the "coin" would roll around corners and drop through gauging slots. The legend "50" was photo-etched (from a master drawn by Ray Gooding) on the faces of the samples since it had already been decided that the new coin would be the first coin of the new Decimal series.