Ghosting on Ceiling
This shows the effects of local thermal patterns. Warm air drives small particles toward colder surfaces
such as the nail heads under the joint compound and paint
"Ghosting" refers to the darkening of areas on the walls or ceiling due to the deposition of particles at
specific locations. These locations are typically areas of local air turbulence or areas where the distance
between two surfaces is small so that the net force of diffusion on small particles is toward the surfaces.
In this case the darkening is due to the formation of small thermal circulation cells. Colder surfaces
produce fewer energetic gas molecules than hotter surfaces. Over years this results in nail heads darkening
and the less insulated areas between joists darkening. The effect shown here required 25 years to form.
Ghosting will appear much more quickly if the turbulence is greater and if there is more soot in the environment.
Significance in the Environment: