This Part of EN 13523 describes the procedure for determining objectively the chalking resulting from natural or artificial weathering of an organic coating on a metallic substrate. The advantage of this procedure for measuring chalking of an organic coating is that the result can be read off immediately on an instrument. Subjective judgement by visual comparison of test specimens with referencee specimens is not necessary. Experience to date with this test method has been based mainly on artificially weathered specimens. Reproductible results can only de obtained by careful execution of the test.