Designation:D660−93(Reapproved2019)StandardTestMethodforEvaluatingDegreeofCheckingofExteriorPaints1ThisstandardisissuedunderthefixeddesignationD660;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(´)indicatesaneditorialchangesincethelastrevisionorreapproval.ThisstandardhasbeenapprovedforusebyagenciesoftheU.S.DepartmentofDefense.1.Scope1.1Theillustratedreferencestandardsincludedinthistestmethodarerepresentativeofdegreesandtypesofcheckingofexteriorpaintfilms.Thesestandardsareprimarilyintendedforcomparativeevaluation.1.2Thisinternationalstandardwasdevelopedinaccor-dancewithinternationallyrecognizedprinciplesonstandard-izationestablishedintheDecisiononPrinciplesfortheDevelopmentofInternationalStandards,GuidesandRecom-mendationsissuedbytheWorldTradeOrganizationTechnicalBarrierstoTrade(TBT)Committee.2.Terminology2.1DefinitionsofTermsSpecifictoThisStandard:2.1.1checking,n—thatphenomenonmanifestedinpaintfilmsbyslightbreaksinthefilmthatdonotpenetratethroughthelastappliedcoating.2.1.1.1Discussion—Whereprecisionisnecessaryinevalu-atingapaintfilm,checkingmaybedescribedasvisible(asseenwiththenakedeye)orasmicroscopic(asobservedunderamagnificationuptotendiameters).3.SignificanceandUse3.1Sincecheckingisnoteasilyrecognizable,thistestmethodisintendedtoprovide,throughdefinitionandillustrations,ameansofevaluatingthedegreeofthisfilmfailure.4.TypesofChecking4.1Manytypesofcheckingarerecognized,ofwhichsomeare:4.1.1IrregularPatternType—Checkinginwhichthebreaksdevelopinthesurfaceofthefilminnodefinitepattern.4.1.2LineandShortParallelType—Checkinginwhichthebreaksinthesurfaceofthefilmaregenerallyarrangedinparallellines.4.1.3SwitchType—Checkinginwhichthebreaksinthesurfaceofthefilmformshortandlongirregularlinescrossingeachotherinawirebrushedpattern.4.1.4CrowFootType—Checkinginwhichthebreaksinthesurfaceofthefilmforminadefinitethree-prongedpatt...
