Visual comparator with test chart and method for evaluating contamination of washing fluids

A method of determining the condition of a mass of previously used cleaning solvent from time to time during use thereof to maximize the extent to which said solvent may be used without recycling, said method comprising utilizing a mass of cleaning solvent to clean mechanical parts for a given period of time, placing a specimen of the solvent thus used into a transparent container, positioning a light source behind a visual comparator having plural viewing apertures therein with said viewing apertures forming an array arranged in a graduated sequence, each aperture including a translucent viewing panel having a color and optical density indicative of the nature and extent of solvent contamination by both soluble materials and dispersed particulates, positioning said solvent specimen so as to facilitate comparing selected ones of said viewing panels and said specimen of solvent to determine whether said solvent requires clarification by reason of the concentration of particulates appearing to be present therein, treating said mass of solvent when indicated with an organic clarifying agent that is miscible with said solvent, thereafter continuing to use said mass of solvent for cleaning, periodically repeating said steps of comparing said solvent specimen with said viewing panels and adding clarifying agent where indicated until a end point particulate concentration is reached which cannot be diminished by the addition of said clarifying agent, or until comparison of said specimen with a viewing panel indicates an undesirably high degree of soluble contaminants, whereafter said solvent may not be clarified and used successfully, and thereafter recycling said solvent to remove particulate materials and soluble contaminants.