What modelling King Charles’s head for the Royal Mint taught me about very public portraits – and royal ears | Martin Jennings

I've sculpted figures from Mary Seacole to George Orwell, but a 9.6m-strong test run of my latest image is art on a whole new scale

The king makes a good subject. Over the months of designing and modelling his head in profile for the British coinage, I have had to examine his features with the scrutiny of a cartographer mapping a landscape.

The process of modelling a bas-relief is painstaking. Commissioned by the Royal Mint, I made a model in plasticine about the size of my outstretched hand and no more than a few millimetres deep. This was then digitally scanned and reduced before dies were struck and coins started pouring into crates. When I was told a test run of 50p pieces was to be produced, I asked how many, imagining a dozen or so. We'll start with 9.6m," came the reply.