A major benefit of the study proposed is to investigate in a relatively timely fashion rather large parameter spaces. For the interest of discussion, only the key findings are reported here but the interested readers will find more detailed discussions in SI, as indicated. Several evaluation criteria are selected to develop an optimal synthesis. It is first considered that obtaining small size Au NPs is more challenging than preparing larger size NPs, in particular for the present case of surfactant-free syntheses prepared in aqueous media. Achieving small size NPs is also ultimately relevant for applications such as catalysis to maximize the use of surface atoms. It is also considered that complying with the principles of Green Chemistry is fundamental to guide the development of new NP syntheses. A sample is therefore defined as optimal if it combines the following properties, in decreasing order of importance: (i) a well-defined surface plasmon resonance (spr) with low ʎspr and/or low Aspr/A450 values with a low ∆ʎ/ʎspr value, to be correlated with small NP sizes with a relatively narrow size distribution, (ii) requires safe chemicals (e.g. low alcohol content and low amount of base), (iii) requires a low viscosity reaction medium, to ultimately facilitate the processing of the Au NPs, (iv) is characterized by a low A650/Aspr value and/or high A380/A800 value indicating more stable dispersions. Each data point is the result of x1 experiment. To guide the reader, the data points corresponding to small NP sizes a re represented in orange and red and the size of the data points is proportional to the corresponding range of λ spr value. An X indicates that no stable colloids were obtained and the sample could not be measured by UV-vis in a meaningful way.