Little is known about the techniques for manufacturing plated coins among the very earliest issues of Greek (and world) money. In this study we present neutron and synchrotron X-ray analyses of a plated silver coin produced in Athens around 525-515 BC. This unpublished coin, ACANS 14A09, is a tetradrachm, which should have been made with 17.2gm of silver. But this ‘false’ coin (with its bronze core) was identified as such in Antiquity, and cut in half so that it might not be used again. Nonetheless, a study of the dies shows that they were used to mint other gorgoneion tetradrachms of good metal and so it is evident that our plated coin was produced in the official mint of Athens, and not by a forger, ancient or modern. Analyses show two mysterious gaps in the silver plating. Apparently the mint repaired the original plating of the coin flan in order to remove two blemishes before it was struck and allowed to pass into circulation.