We report on a synthesis, characterization, and thermal evaluation of a pigmented and silicone-modified medium oil alkyd insulating varnish for antitracking application in rated electrical machines such as traction motors, transformers, and large generators. The varnish is generally applied on the top surface of the main insulation of coils by spray or brush and then baked to remove solvent. The semiconducting pigments entrapped in solid polymer matrix reduces surface corona, flash-over, and tracking of the main insulation by distributing uneven charges from polar or charged particles deposited on the surface after long time use of the machines. The varnish was thoroughly evaluated by means of electrical and mechanical properties over a temperature range. The temperature class of the antitracking varnish was 191.22 degrees C determined by IEC 60216 methods on helical coil bond strength of the cured films. The dielectric strength, tracking, and arc resistance of the pigmented varnish were exceptionally high and it will save core insulation from the tracking, corona and short-time flash-over. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 111: 3065-3073, 2009