Mixing produced in convective flows is investigated comparing three different experiments performed by the authors using brine and fresh water as the two mixing fluids. The initial instabilities are generated by gravitational acceleration and as the flow becomes non-linear the role of local turbulence is examined in experiments of Rayleigh-Taylor driven front occurring across initially sharp density interfaces. The global advance of the fronts is compared with other laboratory experiments and numerical simulations and Mixing Eficiencies are compared and evaluated for a number of different situations with different initial conditions. Using a viscoelastic gel and a plate with holes in experiments similar to those reported by Linden and Redondo (1991), Gonzalez-Nieto ( 2004) the initial instabilities are randomized into a set of plumes in a way in which the initial conditions (viscosity of gel) are seen to modify the overall mixing efficiency.