No matter by what process white lead is produced, it is necessary that it be tested for whiteness and fineness. If on rubbing it out in oil with a spatula it feels gritty, it may be due to being "horny," a term applied by white lead men to dry white lead that has been over-dried on steam pans; in other words, has become crusty, which may also indicate that the pulp has not been thoroughly washed free from lead acetate. Dry white lead of this character, when mixed and ground in oil, does not make good white paint and lacks in opacity (body). If, on the other hand, the grit is due to the presence of uncorroded metallic (so-called blue) lead, it can be readily determined by rubbing out some of the dry lead with a spatula or muller on a white marble slab or with a pestle in a mortar, using turpentine instead of oil as the vehicle, when the metallic lead will show more or less by clinging to the white surface of the marble or mortar. When white lead has this defect it is unfit for grinding in oil for several reasons. In the first place it will coat the face of the millstones and fill the furrows thereof with a coating of metallic lead, thereby preventing fine grinding and greatly retarding the output of the mill, not to speak of the very inferior product that is unsafe to be used as the basis of ready mixed paints for white as well as for tints. First class white lead, aside from the defects just mentioned, should when rubbed up in spirits of turpentine and allowed to dry on clear glass, be a neutral white, as a grayish cast would show the presence of metallic lead in fine division, even if the dry lead be free from grit. If inclined to the yellow cast, it would indicate the presence of massicot or litharge, while a pink cast would show the presence of red lead or orange mineral.