Methods are developed for determining the emission characteristics of enclosed evaporation sources with small apertures and for calculating the composition and thickness of mixed layers by controlling the condensation rates with quartz crystal monitors. For describing the emission characteristics of the sources the cos(n) law is used and a method for determining n is presented. A procedure for calculating the composition and thickness of mixed layers at each point of stationary substrates by measuring the condensation rates is described and the calculated characteristics of the layers are experimentally confirmed by means of analytical, electron dispersive spectroscopy and profilometrical analyses. The procedure is quits simple and does not require knowing the temperature dependence of the vapor pressure of the evaporated substances. It can be used for characterizing all layers obtained by evaporation from one or more sources as well as for selecting the experimental conditions for obtaining layers of desired composition and thickness.