Paint Making

If your motive is to create colors not available in model paints, you can merely mix the appropriate colors of the model paints.

Many of the good brands of model paints use pigments more finely ground than used in regular paints.  The big companies that sell model paints do a pretty good job of creating good paint and it would be hard for an individual to make better ones.

I do remember reading articles in very old mags like pop mechanics (they used to run many articles on model building- especially sailing ships) about making custom varnishes for wooden models.  Magazines for modeling have occasionally run articles on modifying commercial model paints.  Flying modelers add "plasticizer" for reducing shrinkage of coverings.  Before model companies came out with flat paints the popular trick was to add talcum powder to gloss paints to make your own flats.

I am curious about something which has me answering with a question. Why do you want to do that with the variety of paints available to the modeler these days?

Interesting question though and one I don't recall being asked.  I'll too will be watching for the responses.