Guar and xanthan gum products exhibit this flow behavior. A yield point must be reached before flow begins. Mayonnaise and margarine are plastic substances. When the shear rate increases, the viscosity increases. Starch suspensions and some chocolate syrups exhibit dilatant flow.
Fluids also can exhibit time dependent or directional viscosity characteristics.
A Thixotropic fluid's viscosity decreases at a constant shear rate over time. If the viscosity reverts to its original level at some point with the cessation of shear it is called reversible. But as this term is often misused to indicate pseudoplasticity, it is best avoided. Many gums and starches are thixotropic. On the other side, a Rheopectic fluid's viscosity increases with a constant shear rate over time.