Herein provided are methods for determining deposition of contaminants significantly influencing machine runnability or product quality in manufacturing processes of pulp and paper, especially determining the degree of deposition and the morphology of deposits of sticky contaminants or pitch and for evaluating the effect of chemicals for reducing deposition.In a manufacturing process of pulp and paper is used a method comprising: determining the degree of deposition of a contaminant from a liquid or slurry on a quartz crystal oscillator; and quantifying the morphology of deposits on the surface of the quartz crystal oscillator by image analysis. Further, a method comprising adding a chemical for reducing deposition to the liquid or slurry and then quantifying the degree of deposition and the morphology of deposits is used to evaluate the effect of the chemical.