Abstract: We have recently experimentally, analytically, and numerically demonstrated the nonlinear photo-induced plasmon-assisted magnetic response that occurs with 80-nm gold particles in aqueous solution. The anomalously-large magnetic response—theoretically considered too small to observe at room temperature— was observed using light from a solar simulator and small (micro-to-milli-Tesla) magnetic fields.  I will explain why the effect is observable using disperse nanocolloidal liquids, and present our theoretical model of an increased and anisotropic electrical conductivity, which yields modified absorption spectra in agreement with our experimental results. This work, which is the first nano-demonstration of old physics, improves our fundamental understanding of surface charges in nanostructures and aids the development of broad-band photonics metamaterials, new polarization-encoded imaging methods, photocatalytic materials, photovoltaic devices, and sensors.