Many colloidal dispersions show Bingham flow which is characterized by a σ-D diagram as shown. At rates of shear greater than that at point A, the following relation applies: $$\sigma -{\sigma }_{\text{B}}={\eta }_{\mathrm{\Delta }}D$$ where ${\sigma }_{\text{B}}$ (or ${\tau }_{\text{B}}$) is called the Bingham yield stress, ${\eta }_{\mathrm{\Delta }}$ 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.