Most of us know that when you mix two substances together there’s no way of returning them to their original state. For example mixing some colors in water

This is true for non-viscous fluids. On the other hand, if the same thing is done with glycerine you will be able to return the fluids to their original state before mixing by simply un-mixing the fluids. This can happen because, unlike water, glycerine is a viscous fluid. The video below demonstrates this interesting phenomenon.