Colloidal nanoparticle gold can be formed by resolving chlorauric acid by using the wet method, and nanoparticle gold having diameter ranging from 2 nm to 80 nm can be formed by choosing conditions of reducing agent. Particle diameter of these nanoparticle gold is in the range of about ±10% and are very uniform. Nanoparticle gold having diameter of 6nm or over presents a unique optical characteristic called plasmonics. The most understandable characteristic is that transmitted light becomes red which occurs with particles having diameter of about 10 nm. This characteristic has long been used as a coloring agent for the bronze-red color.
We have technologies that enable manufacturing of nanoparticle gold having various particle diameter with excellent controllability.