a single pigment that will do what pigment must do, until a better medium is found for paint-making than linseed oil; namely, "take and retain the binder, cover and obscure the surface," prolong the life of the oil, and make it dry fast enough for practical use. Certain solids, under certain conditions and in certain proportions, have mutual action upon each other; they interchange elements and combine to form new substances, just as metals alloy and form new metals. Now, applying this truth to pigments: In order that chemical combination may follow, or that that which is bad in one pigment may be linked with that which is bad in another, to produce a new pigment  that  is  good,  it  is  necessary  that the solids under consideration be very finely divided,  very  closely  intermingled;  and  that   the   affinity   between   them   be  great