Upon adding HAuCl4 to an alkaline solution of 80 v.% water and 20 v.% alcohol the solution turns grey, blue, purple and finally red, indicative of the formation of Au NPs with a characteristic spr around 520 nm in UV-vis characterization. The synthesis proceeds in a similar way when methanol, ethylene glycol or glycerol only (only one alcohol) are used, with however different kinetics and leading to different NP sizes, which is attributed to the different redox and physico-chemical properties of the different alcohols . The alkaline conditions favor the formation of alkoxides from the alcohols that play the role of reducing agents for the RT process . The general mechanisms behind the NP formation are detailed in length elsewhere , and further discussed below in light of the results reported. A first finding here is that Au NPs are also obtained when mixtures of [ethanol+glycerol] are used, as illustrated in Figure . and NP diameter (○, left-hand side axis) retrieved from STEM analysis as a function of different alcohol contents and mixtures, as indicated. The source of reducing agent was ethanol only in various contents, in various ratios, and glycerol only in various contents, as indicated. The X indicates samples for which the plasmon resonance is not well pronounced: 1 and 2 v.% Ethanol. Et: Ethanol; Gly: Glycerol. See Figure for UV-vis spectra and Figure for further correlation between λspr and diameter. In all cases 0.5 mM HAuCl4 and 2 mM NaOH were used.