However, the sparseness of the concentrations should be noted and addressed for log transformation, as 0 maps to -∞. First solution to address the sparseness is to featurize by the precursor's role, in this case specifically, gold source (gold chloride), capping agent (e.g. CTAB, citrate), reducing agent (e.g. borohydride, ascorbic acid). This way, a data point would be featurized as a fixed-size vector consisted of each role's material embedding and its However, in AuNP synthesis, there are often cases involving "additives" that have unclear roles (e.g. acids, metal cations), have more than one capping agents, or have a chemical that serves as both reducing agent and capping agent.