Having established that (i) ca. 20 v.% ethanol is suitable to obtain relatively small size Au NPs in a low viscosity solvent and that (ii) low amount of glycerol are suitable to induce the Au NP formation, we now turn to investigate mixtures of [ethanol+glycerol] in different relative ratio but keeping the total amount of alcohol at 20 v.%, see Figure A more detailed screening of the influence of low amount of glycerol is proposed in Figure together with repeated experiments that confirm the trend observed, see Figure -S6 and S8. These results indicate that the NP size decreases as the amount of glycerol increases to ca. 5 v.%, while the viscosity of the reaction mixture increases as the glycerol content increases. 17 It is therefore concluded that small amount of polyol in the range 1-5 v.% can help controlling the NPs size towards smaller size as the amount of glycerol increases. Importantly, this small amount of viscous polyol does not change much the overall viscosity of the samples still obtained in relatively low viscosity media containing mainly water and ethanol.