This journal article describes research on techniques for the identification and prevention of mould (mold, fungus, mildew) growth on painted surfaces in the manufacturing industry by the Nuodex Microbiological Laboratories. Examination using a vertical illumination microscope attachment distinguishes morphological details (eg. mycelium), enabling taxonomic classification of the discoloring agent directly from the paint film. Stereoscopic microscopy reveals the presence of filaments and establishes the presence of erupting type moulds such as Phoma sp.. While most pigments and extenders impart some mould resistance, anti-fungal paints are best achieved by proper formulation, and addition of an effective fungicide. Cresol mercury napthalate appears promising in low viscosity hydrocarbon solutions. Permanent and insoluble in water, it will not leach or crystallize out. It does not affect color, drying time, film hardness or durability and the final film is both non-toxic and non-corrosive. This article is a reference for protective coatings and mould inhibitors. It may have certain conservation applications. References date from 1940-1948.