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In contrast to thixotropy (destruction of the structure of a fluid by shear forces and its reconstruction after a period of inactivity), rheopexy is a phenomenon in which low shear forces promote the building of structures in a fluid. Discovered by Freundlich, rheopexy can be observed by executing the following experiment: pour a thixotropic suspension composed in 42% of 1-10 µm sized gypsum particles into a 1 cm thick test tube, shake it and then allow it to rest. The mixture hardens after 40 minutes. By slowly turning the test tube on its axis between your palms, the plaster begins to solidify after only 20 seconds, i.e. 120 times sooner. The reason for this is that the strong shear forces acting on the contactors destroy the structure of the fluid and convert it into a sol while the relatively low force acting during rotation accelerate its hardening.