This part of ISO 787 specifies a general method of test for determining the resistivity (specific resistance) of the aqueous extract of a pigment. The method is applicable to all pigments and extenders, except pigments that are substantially soluble in water. It should be noted that the resistivity of the aqueous extract of a pigment should be considered as a property independent of the amount of water-soluble matter. If agreed, a cold extraction method may be used. This shall be stated in the test report, however. The standard temperature of determination should preferably be 23 °C but a different temperature may be agreed between the parties provided that the necessary corrections are made to take account of the differences in temperature. NOTE When this general method is applicable to a given pigment, a cross-reference to it will simply be included in the International Standard relating to that pigment, with a note of any detailed modification which may be needed in view of the special properties of the pigment in question. Only when this general method is not applicable to a particular pigment will a special method for determination of resistivity of aqueous extract be specified.