ISO 1518-1:2019 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 outa) either as a "pass/fail" test, by testing with a single specified load applied to the stylus to assess conformity with a particular specification, orb) as an assessment test by applying increasing loads to the stylus to determine the minimum load at which the coating is penetrated.NOTE Neither this document nor ISO 1518-2 specifies a method using a curved stylus, which is specified in ISO 12137. The choice between the three methods will depend on the particular practical problem.