Fluid dynamics and Pollock’s paint applicators

Authors Andrzej Herczyński, Claude Cernuschi, and L. Mahadevan (“Painting with drops, jets, and sheets,” PHYSICS TODAY, June 2011, page 31 ) describe Jackson Pollock’s painting technique and purport to explain the physics underlying the flow of paint by scaling relations, given in their equations 1, 2, and 3. Their scaling relations, however, are for a Newtonian viscous fluid, for which the shear rate is proportional to the shear stress. But paint is a complex non-Newtonian fluid that does not satisfy this linearity requirement. ¹ Experiments with a cylindrical wooden rod initially dipped into a container of ordinary wall paint can readily show that the scaling relations do not conform with observations.

For a video showing the formation and shape of Pollock’s paint jet, see http://www.youtube.com/watch?v=ajZCjlxv7GI . Observe that the shape of an actual jet does not conform with the theoretical shape shown in figure 4b of the article, because the authors drew the figure without taking into account that paint also is an incompressible fluid. This property implies that the initial radius of the jet is smaller than the radius of the rod, as observed in the video, instead of larger, as shown in figure 4b.