Black pigment, process for its preparation and its use

Abstract

Building materials such as concrete can be colored by a black pigment which consists essentially of manganese ferrite of the composition Mn.sub.1+x Fe.sub.2-x O.sub.4 with a spinel structure wherein x has a numerical value from -0.1 to 0.1 and the pigment is prepared by a process wherein a) soluble manganese (II) salts and soluble iron (II) salts are precipitated from a solution of metal salts by reaction with alkaline precipitating agents in an approximately stoichiometric ratio, b) the precipitate from a) is reacted with an oxidizing agent to form a pigment, and c) the pigment is filtered, washed, dried and ground.

Dependencies are inferred from the claim text.