To provide a first interpretation of the differences reported and discussed below, experiments were performed without base as detailed in section S6. The position of the peak around 300-325 characteristic of HAuCl4 nm shifts towards higher wavelengths with the different alcohols used as source of reducing agents in the order methanol < ethanol < EG < glycerol. This position of the peak also shifts towards higher wavelengths with an increasing content of alcohol. Only the polyols absorb between above 250 nm. A HAuCl4-water-alcohol-and-alcohol-content interplay is then likely to account at least for part of the results discussed below. In particular, the absorption properties of the alcohol might play a significant role.