1.1 General This International Standard outlines general methods for determining the average surface density over a measured area of anodic oxide or of a coating deposited autocatalytically, mechanically, by chemical conversion, by electrodeposition, by hot dip galvanizing and by vacuum using gravimetric and other chemical analysis procedures that have attained some degree of national or international standardization. A variety of procedures are described and include: — gravimetric procedures for chemical or electrochemical dissolution of the coating or the substrate to determine the coating surface density; — analytical procedures that utilize dissolution of the coating for photometric or volumetric determination of the coating surface density; — non-destructive instrumental physical analysis of the coating to determine the surface density. With the exception of the gravimetric method described in ISO 3892:—, this International Standard does not give the measurement uncertainties of the methods cited. 1.2 Sources The stripping methods cited in annex A are described in specifications in the open literature or have been used routinely by at least one laboratory. 1.3 Restrictions The procedures described can be used for many coating-substrate combinations. They cannot be used where neither the coating nor substrate material can be completely removed, one from the other by chemical or physical means and there is a constituent common to both that is not readily separated (e.g. nickel phosphorus alloy on nickel). NOTE The measurement of very thin coatings on very small pieces can result in a reduction in accuracy and a lack of repeatability. Several measurements using a combination of different procedures on similar samples might overcome this situation. 1.4 Limitations In principle, the gravimetric procedures can be used to measure very thin coatings or to measure coatings over small areas, but not thin coatings over small areas. The limits depend on the required accuracy; e.g., 2,5 mg/cm2 of coating might require 1 cm2, but 0,1 mg/cm2 of coating would require 25 cm2 to obtain 2,5 mg of coating. These limitations do not apply to the chemical analysis methods. The gravimetric method does not indicate the presence of bare spots or sites with thicknesses lower than the specified minimum in the measuring areas. In addition, the single value obtained from each measuring area is the mean thickness of that area. There can be no further mathematical analysis of this single value, for example, for statistical process control purposes.