Reports on the results of experiments to test for visual changes to paint systems after biocidal treatments, using a statistical binary procedure. Four biocides were selected, two of which are fungicides--a quaternary ammonium-organotin mixture (BioMet 66®) in distilled water and an orthophenyl phenol (Lysol ®) in a spray--and two of which are fumigants--sulfuryl fluoride (SO-2</sub>F-6</sub>), a gas (Vikane ®), and nitrogen gas (N-2</sub>) (a s an anoxant). The procedure used to assess the effect of the biocidal treatments was a random field visual scoring regimen by two paintings conservators. The tests were conducted on 30 combinations of linen, rabbit-skin glue size, lead white oil ground, and oil-based paints. The visual assessment procedure provided information on color change, gloss change, blanching, topography change, and precipitation. The results indicated that Vikane adversely affected 10 of 11 pigment systems Lysol adversely affected six of 11 pigment systems; BioMet 66 had a minor effect on four of 11 pigment systems; and nitrogen had no visible effect on any sample. The visual technique provided a quick and broad method for assessment of nonsubtle visual changes.