A Schlieren optical setup allows the direct visualisation of gradients in chemical composition or temperature. It has been used for instance to measure the influence of chemical reactions on CO2 sequestration.
A snapshot of the plumes developing below the interface when gaseous CO2 dissolves in a 0.1mol KOH solution. More information can be found here: http://bit.ly/2czU243
Visualisation of ice growth in saline water shows instabilities induced by the rejection of brine of the growing ice layer. More information can be found here: http://bit.ly/2dt48UT