Employed at the Paris Mint, then the Royal Mint from 1820, his most famous work was the obverse portrait of George IV from 1821, after an original work by Sir Francis Chantrey. The King had disliked the 'overweight' effigy Pistrucci had designed, preferring the Chantrey portrait. Merlen was given the task of engraving the Chantrey image after Pistrucci refused to redesign the effigy following the work of another artist. Merlen's effigy is also notable for being the first to show a male monarch bareheaded, i.e. neither crowned or laureate (in the style of Roman emperors) since the reign of Edward VI.
Merlen also designed several reverses, the most widely used being a crowned shield surrounded by a wreath, variants of which were used in issues of William IV and later Queen Victoria. His designs for the reverses of maundy money remained in use until 1887.
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