We report the results of treating a dense, chemically produced silver colloidal suspension with high-power laser pulses and with exposure to supercritical water (SCW) conditions. The initial colloid has a mean particle diameter measured by transmission electron microscopy to be 28.4 run and exhibits a broad absorption band in the visible region with a small maximum near 420 nm. Both treatments result in smaller particles. The laser treatment fragments the original colloidal particles and produces an average particle diameter of 5.4 nm. The SCW treatment appears to dissociate aggregates in the original colloid, resulting in particles with a mean diameter of 9.9 nm. Plasmon resonances for the two colloids produced by these treatments appear at 400 run and 390 ran for laser- and SCW-treated colloids, respectively. The plasmon resonance of the laser-treated colloid is typical of small silver colloids produced by most methods, whereas the 390-nm resonance of the SCW-treated colloid implies a strongly negative colloidal surface charge.