Many colloidal dispersions show Bingham flow which is characterized by a $\upsigma\!$-D diagram as shown. At rates of shear greater than that at point A, the following relation applies: \[\sigma - \sigma _{\rm{B}}=\eta _{\Delta }\ D\] where \(\sigma _{\rm{B}}\) (or \(\tau _{\rm{B}}\)) is called the Bingham yield stress, \(\eta _{\Delta }\) is the differential viscosity, \(D\) is the shear rate, and \(\sigma \) is the average of three normal stress components if the deformation is purely dilatational.