This part of ISO 787 specifies a general method of test for determining the percentage by mass of matter soluble in cold water, in a sample of pigment or extender. ISO 787-3 specifies a method for determining the percentage by mass of matter soluble in water by hot extraction. For most pigments and extenders, these two test methods will give different results, and it is therefore essential to state clearly in a specification which method is to be used, and in the test report which method has been used. NOTE The general methods given in the various parts of ISO 787 are usually applicable to any pigment or extender. Thus only a cross-reference to the appropriate part of ISO 787 needs to be included in the International Standard giving the specification for that pigment or extender, indicating any detailed modification that may be needed in view of the special properties of the material in question. Only when the general methods are not applicable to a particular material is a different method for determination of water-soluble matter to be specified.