Schlieren photography is a tool used by researchers to study air currents and shock waves. It shows changes in air density (index of refraction). Usually schlieren images only show the mirror (where the effect can actually be seen in the light and dark patterns). So, I decided to make an image (the first such image to my knowledge) that combines schlieren and and the surroundings. The match was just lit which created the blue smoke. You can see the schlieren effect in the turbulent hot air currents rising in front of the mirror.
I hope it fits the theme as it uses and shows a lab technique used in fluid dynamics.