In 1964 Machin was chosen to design a new effigy of the Queen for the decimal coinage, which was to be introduced from 1968. This was used for all British coins until 1984 and was also used on the coins of Rhodesia in 1964, coins of Canada from 1965 to 1989, Australia from 1966 to 1984 and New Zealand from 1967 to 1985. In 1966 the Queen approved Machin's similar design for an effigy of her to be used on what came to be known as the "Machin series" of British definitive postage stamps. Machin produced a bas-relief in clay which, when combined with a different coloured background, is reminiscent of the overlaid decoration of potteries such as Wedgwood. The design was first used on the 4d stamp which was issued in June 1967, and has been used on all British definitive stamps since. It is thought that this design is one of the most reproduced works of art in history with, to date, approximately 320 billion copies produced. On several occasions the Queen has been approached with suggestions for the replacement of the Machin stamp portrait. Although she has considered alternatives, she has never approved any new design, stipulating that any such replacement would have to be "a work of real quality". In 2007 the Machin-designed stamp was still in use at its 40th anniversary and to mark the occasion, the Post Office issued a commemorative stamp featuring a photograph of Machin. It was also available for sale in a miniature sheet which incorporated another stamp with a reproduction of a Machin series stamp, as well as two £1 Machins in different colours.
Conservation
In the year 1956, while resident at number 15The Villas, Stokeville, an estate of 24 Victorian houses in Stoke-upon-Trent, he received publicity in the national press when he chained himself to an old metal lamp-post, in protest at its planned removal. Machin's protest, "against the destruction of all the beautiful things which is going on in this country" did not prevent the lamp-post from being replaced by a concrete one; however, it was given to him for his own garden and his wife Patricia unlocked him. The lamp has since been restored to its original position.
Family
Machin and his wife had a son, Francis, who was also an artist, and an architect. After Francis died, some of his father's possessions, from his house near Eccleshall in rural Staffordshire, were sold at auction. These included the fourth of the known final plasters made to create the Machin stamp series, the three others being kept in the Royal Mail archives. Minor planet3109 Machin is named in his honour.