Hard gold deposits plated from an additive‐free phosphate bath have been analyzed for codeposited inclusions using transmission electron microscopy. Electron diffraction analyses of residues obtained from aqua regia dissolution of the gold deposits and those collected from the surface of thermally aged deposits showed that these residues consist of aurous cyanide . These results and other electrochemical evidences suggest that is codeposited in additive‐free hard gold, bringing about a grain refining effect and the resulting increase in hardness.