  The spreading of a thin film of suspension on a spinning disk and the
accompanying contact line instability is studied through flow visualization
experiments. The critical radius for the onset of instability shows an increase
with increase in the particle fraction ($\phi_{p}$) before decreasing slightly
at the highest value of $\phi_{p}$ studied, while the instability wavelength
($\lambda$) exhibits a non-monotonic dependence. The value of $\lambda$ is
close to that for a partially wetting liquid at lower $\phi_{p}$, it decreases
with increasing $\phi_{p}$ to a minimum before increasing again at largest
$\phi_{p}$. The non-monotonic trends observed for $\lambda$ are discussed in
light of the linear stability analysis of thin film equations derived for
suspensions by Cook {\it et al.} [Linear stability of particle-laden thin
films, Eur. Phys. J.: Spec. Top. {\bf 166}, 77 (2009)] and Balmforth {\it et
al.} [Surface tension driven fingering of a viscoplastic film, J. Non Newtonian
Fluid Mech. {\bf 142}, 143 (2007)].
