I was trying to model experimentally the interdiffusion of two miscible liquids. Is there an optical method to find out the extent of diffusion; the addition of fluorescing agent into any of the two fluids would work, but will it not influence the diffusion process by changing the chemistry of the fluid itself?
Have 2 color dyes with a 0 reactivity like yellow and blue. Once you have ideal diffusion it should appear green. Liquid steel a type of glue that you have to kneed to activate and are composed of 2 halves of white and grey. When mixed properly there would be no visible traces of either color but a solid light grey.
When dealing with transparent liquids a color chart of can be made to cross reference if you need more of one or the other fluid.
Consistency of the dye is important but can be tested before use by measuring the weight of the dye and how much it changes the liquid's color.