Can some one suggest a color molecule of about 0.2 microns size, and which is water soluble? I want to use this in solution on our microfilter(cut off at 0.1 micron) to see if it works properly. This could be routine check.
You should be able to get these pigments at most art stores and any university art supply. All of them are water based and relativly non-toxic. Make sure to stir them completely to break up any settling and floccing that may have occured.