This part of ISO 787 specifies a general method of test for determining the electric resistivity (specific electric resistance) or the specific electric conductivity, respectively, 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 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. 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.