This part of GSO ISO 1518 specifies a test method for determining under defined conditions the resistance of a single coating or a multi-coat system of paint, varnish or related product to penetration by scratching with a scratch stylus loaded with a specified load. Penetration of the stylus is to the substrate, except in the case of a multi-coat system, in which case the stylus can penetrate either to the substrate or to an intermediate coat. The method specified can be carried out a) either as a “pass/fail” test, by testing with a single specified load applied to the stylus to assess compliance with a particular specification; b) or by applying increasing loads to the stylus to determine the minimum load at which the coating is penetrated.