We have demonstrated that nanoparticle shapes may be tuned by varying the stirring time in the formation of sub-3 nm Ag nanoparticles by a thermal reducing process. Short term stirring gave Ag nanoparticles with very anisotropic shapes having one or more sharp tips. Long-term stirring eliminated the sharp tips, thereby forming ellipsoidally shaped nanoparticles. The loss of sharp tips appeared as a blue shift of the localized surface plasmon resonances of Ag nanoparticles, exhibiting a significant color change under dark-field microscope. In addition, the line width of the nanoparticle spectra became narrower as the sharp tips were lost. (C) 2007 Elsevier B.V. All rights reserved.