To understand better the effect of such a small amount of glycerol on the control of the NP size, we performed kinetics study on the formation of the Au NPs. eye) when glycerol is used compared to the use of ethanol only. When [ethanol+glycerol] mixtures are used, and even with small amount of glycerol such as 2 v.% glycerol with 18 v.% ethanol, an overall faster appearance of a red colloidal dispersion can be observed with the naked eye compared to the case where ethanol only is used. The overall formation pathway considering various metrics is confirmed to be faster for [ethanol+glycerol] compared to the case of 20 v.% ethanol without glycerol, see Figure . (Amax) 1/3 is proportional to R(N) where N is the number of particles and R their radius. The general features of the time-resolved data resembles those reported by others, for example on study considering the citrate-mediated synthesis of Au NPs. The plot of (Aspr) 1/3 as a function of time can be dived in to three phases: (I) An initial region where (Aspr) 1/3 increases in a superlinear fashion; (II) an intermediate region where (Aspr) 1/3 increases linearly; and (III) a final region where (Aspr) 1/3 exponentially increases and levels off to its final value. For clarity, those phases (I-III) are indicatively illustrated in Figure . Those phases have been attributed to: (I) NP grow via aggregation: Coupled to SAXS measurements, it was established in previous work that the number density of the NP decreases, while the particle size increases in phase I; (II) no further aggregation occurs, and the particles grow linearly in time via a surface growth reaction; and (III) NP size grows via an autocatalytic growth stage and levels up to its final value. Here, in agreement with previous results, the formation of the Au NP using 20 v.% glycerol (no ethanol) is rather fast in the initial steps of the synthesis, followed by a slow and continuous growth, which is attributed to the redox properties of glycerol and its high viscosity, respectively. Also in agreement with previous report for the ethanol mediated synthesis (no glycerol), the phases I and II are almost merged which is attributed to the fast formation of the first NPs seeds in absence of stabilizers in the low viscosity solvent together with a slow autocatalytic growth due to the room temperature process. In the case of [ethanol+glycerol], the same phases are observed but the reaction proceeds faster than when only ethanol is used. Importantly, the time normalized data from 20 v.% ethanol and [ethanol+glycerol] with 18 v.% ethanol and 2 v.% glycerol follow the same general dynamic illustrated in Figure . This suggests that glycerol mainly plays a role to accelerate the initial steps of the synthesis. Since all conditions lead to approximatively the same final (Aspr) 1/3 values , and assuming that using different alcohols does not change too much the properties of the medium surrounding the Au NPs and hence their optical properties, and given the larger size of the resulting NPs when ethanol only is used, as detailed in Figure , it can be concluded that the number of final NPs obtained in presence of glycerol is higher than without. Therefore, the difference observed can be interpreted as follow: small amount of glycerol favors a faster formation of the initial seeds. Assuming that the classical nucleation theory applies here, this fast formation of the seeds followed by a slow growth leads to the observed smaller and more monodispersed NPs compared to the case where only ethanol is used (where the use of ethanol only is characterized by a slower nucleation process). The fast formation is observed with amount of glycerol as low as 2 v.%.