  Drying a droplet of colloidal dispersion can result in complex pattern
formation due to both development and deformation of a skin at the drop
surface. The present study focus on the drying process of droplets of colloidal
dispersions in a confined geometry where direct observations of the skin
thickness are allowed. During the drying, a buckling process is followed by a
single depression growth inside the drop. The deformation of the droplet is
found to be generic and is studied for various colloidal dispersions. The final
shape can be partly explained by simple energy analysis based on the
competition between bending and stretching deformations. Particularly, the
final shape enables us to determine precisely the critical thickness of the
shell for buckling. This study allow us to validate theory in 2D droplets and
apply it to the case of 3D droplets where the thickness is not accessible by
direct observation.
