What kind of spray injectors does the chemical industry use presently? On rocket engines, coaxial injectors
have brought big improvements by making a finer mist. Drawings there for instance:https://www.jstage.jst.go.jp/article/tjsass/50/169/50_169_201/_pdf
with one injector element on page 204 and the injection head on page 206 (pages 4 and 6 of the pdf).
They often inject the swirling liquid at the center and shear it by the outer gas, but some excellent engines (RD-170) do the opposite.
The industrial version of a mortar and pestle is for instance a ball mill
, to crunch the spheres:http://en.wikipedia.org/wiki/Ball_mill
you could experiment with bearing balls in a concrete mixer. With a pigment, it would be dirty for real.
Though I wonder if one can get a powder of 500nm size without chunks. Graphite, which is little sticky (I suppose a pigment sticks much more), always makes chunks. That's why I suggested - if possible - to mix the pigment with the binder first
, and only later evaporate the solvent; so to say, the pigments would stick to the binder rather than with another.
You might also take the hollow pigment spheres, mix them with the binder - if your product alllows this - and then break the spheres, say by a strong shear in the binder, as some miniature chemical reactors do to mix the reactants.