Fluid flow and fluid evaporation both contribute to the overall rate of thinning during spinning of a fluid on a disk. Laser interferometry of solvent thinning behavior on spinning silicon wafers was performed to yield plots of solvent thickness evolution. These plots of thickness versus time were then analyzed to understand the respective contributions of viscous flow and evaporation to the thinning. A technique is described for extracting both the viscosity and the evaporation rate from the interference data. Well understood solvent systems are examined as test cases for this deconvolution. It is also demonstrated that nonevaporating fluids can be analyzed, even though their thickness evolution has no easily referenced endpoint to the thinning, in contrast to the volatile solvents which are rapidly spun dry. ©1997 American Institute of Physics.