Abstract: In spin coating a liquid magnetic dispersion onto a rotating annular substrate, a stationary fluid barrier member is positioned closely adjacent the substrate after deposition of the dispersion thereon and during the time the excess dispersion is spun off, the substrate has a radial opening therein which permits fluid communication between the outer portion of the fluid barrier and its inner portion. The barrier member serves to reduce the rate of solvent evaporation from the dispersion so that the dispersion flows more readily during spin-off to produce a thinner resulting magnetic coating.