Ultrafine (∽ 20 nm diameter) gold particles produced by the reduction of an aqueous AuCl3 solution with citric acid have been used as model systems for the study of structural control in systems of nanometersized colloids and for the study of sintering between such particles.Liu has observed that the final, monosized particles evolve from sintered (welded) aggregates (Fig. 1). This process is visible as the color of the gold suspension changes over time. Liu also noted that the ultimate particle size was a function of the gold/citrate ion ratio in the original solution. Similarly, Ferguson et al. have observed the low temperature welding of gold surfaces when organic adsorbates move laterally to increase metalmetal contact. Although Liu has shown that aggregation and deaggregation processes are important in the evolution of colloidal particles, no explanation has been given for the dewelding mechanism of larger aggregates to form discrete particles. In this work, we combine the techniques of electron microscopy and infrared spectroscopy to propose a chemical influence for the dewelding process.