Protection coatings with additional fillers, very porous or of unusually compact structure, are discussed, i. e., silver on ceramic ware. Thickness must be defined. To obtain reliable data two values should be determined: the geometric thickness and the concentration of metal in the measured layer. The results depend not only on the characteristics of the layer, but also on the method used for measuring (i.e., microscopic, coulometric or complete dissolution). -- AATA