This European Standard specifies a method of assessing the quality of sealed anodic oxidation coatings on aluminium and its alloys by measurement of the loss of mass after immersion in phosphoric acid/chromic acid solution with prior acid treatment. A related standard (EN 12373-6 1) ) describes the same method used without prior acid treatment. The method is particularly applicable to anodic oxidation coatings intended for architectural purposes. For less severe applications, the method described in EN 12373-6 1) may be more suitable. The method is not applicable to: - hard-type anodic oxidation coatings which normally are not sealed; - anodic oxidation coatings that have been sealed only in dichromate solutions; - anodic oxidation coatings produced in chromic acid solutions; - anodic oxidation coatings that have undergone a treatment to render them hydrophobic. The method is destructive and can serve as a reference method in case of doubt or dispute regarding the results of the test for loss of absorptive power (EN 12373-4 1) ), or the measurement of admittance (EN 12373-5 1) ).