With initial [AgNO3] of 3.0 × 10−4 M and microwave
heating times of 30−60 s (or conventional gentle boiling for 3−
5 min), the absorbance of the sol is usually between 0.8 and 1.2.
The sols are stable and retain their yellow coloration
indefinitely. Addition of an electrolyte such as NaCl has no
visible effect; this contrasts with silver nanoparticles produced
by borohydride reduction, which typically aggregate into larger
particles with a color change to gray/brown unless a stabilizer
such as polyvinylpyrrolidone (PVP) has been added.3 When a
laser pointer is directed through the sol, the laser beam is visible
(Figure 2); this is a manifestation of the Tyndall effect which is
observed for colloidal dispersion.23