This part of ISO 787 specifies general methods of test for determining the density of a sample of pigment or extender, using a Pyknometer. ISO 787-23:1979 , General methods of test for pigments and extenders — Part 23: Determination of density (using a centrifuge to remove entrained air), specifies a general method using a centrifuge to remove trapped air. NOTE 1 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 density to be specified.