The intermetallic compound Al2Au, also known as purple gold, has elicited much interest due to its unusual optical properties.The precipitation of this compound in Al alloys, however, for example in interconnects of integrated circuits, can be a serious problem (the so-called Purple Plague).Al2Au precipitates (or the η phase) are also interesting owing to their similar crystal structure and precipitation behaviour compared with the intermediate Al2Cu (θ) phase in high-strength Al-Cu alloys.Recently the θphase has been found to exhibit unexpected and complex interfacial structures, and the question naturally arises as to whether the η phase also exhibits such structures.