Understanding the underlying mechanism for the synthesis of metallic nanoparticles is crucial for strategic creation of desirable particles. We have recently designed a correlative approach to detect, visualize, and characterize intermediate species during a seedless, anisotropic nanoparticle synthesis. We showed how EPR radical signals of intermediates during a nanoparticle reaction can be combined with optical and structural properties of particles at specific time points to provide insight into the mechanism of seedless nanoparticle growth. We demonstrated that changes in radical intensity can be considered as an indicator of nanoparticle structure and properties. By correlating known analytical tools in new ways, we quantified intermediate reaction species and unlocked new information about the seedless formation of anisotropic nanoparticles. This correlative approach can be used as a multi-faceted method to determine intermediate species during synthesis and reveal new information about radical-based nanoparticle formation.