We studied sodium and ammonium gold sulfites as gold salt in a 45°C bath, and compared hardness.
Conventional sodium gold sulfite bath deposits have a Vickers hardness of about 110Hv at 45°C.
Deposits in an ammonium gold sulfite bath containing 200g/L of ammonium sulfite monohydrate had a Vickers hardness of about 90Hv at the same bath temperature.
Ammonium gold sulfite bath deposits had a fully bright appearance free of metallic additives.
