A slurry containing water, carbonate-containing pigment, and dispersant consisting of 25-70 % by weight of agglomerated carbonate-containing pigment, 0.1-1.0% by weight of a dispersant, the balance being water up to 100%, can be used advantageously in papermaking as well as in the paint and lacquer industry. In a novel process for agglomerating ultra-fine particles in slurries the slurry is subjected to heat treatment until the agglomeration is complete.

A pigment material for use in a coating composition suitable for coating a sheet material to be printed by an electrophotographic printer which pigment material comprises a blend of Components A and B as follows: Component A: a fine pigment material suitable for gloss coating of a sheet material the pigment material comprising particles at least 80% by weight of which have an equivalent spherical diameter ("esd") of less than 2 .mu.m and having a particle size distribution ("psd") such that its d.sub.50 value, namely the particle esd value less than which 50% of the particles have an esd, is less than 1 .mu.m; and Component B: a coarse pigment material having a psd such that its d.sub.50 value is from 2 .mu.m to 10 .mu.m, desirably 2 .mu.m to 5 .mu.m and such that not more than 2% by weight of the particles of the coarse pigment material have an esd greater than 15 .mu.m, desirably not more than 2% have an esd greater than 10 .mu.m; wherein the weight ratio of Component A to Component B is at least 4:1.

Composite compounds of co-structured or co-adsorbed organic or mineral fillers or pigments containing at least two organic or mineral fillers or pigments of a different nature and the use thereof in the paper industry for manufacturing paper, filling or coating or for any other surface treatment of the paper as well as wood or metal or plastic or cement surface treatment compounds in the fields of aqueous and non-aqueous prints and plastics materials. Coating colors, uncoated filling compound and sheets of base paper for coating containing them.

A process for producing calcium carbonate particles having an average size of 0.3.+-.0.1 .mu.m, the process comprising the steps of preparing light calcium carbonate particles of 0.6.+-.0.4 .mu.m in average size by carbonating calcium hydroxide suspended in water, drying and pulverizing the light calcium carbonate particles, admixing the dry powders thereof with a dispersing agent, and wet-grinding the slurry. The final product imparts high opacity and brightness to coated papers when it is used as a pigment.

A multi-component pigment slurry which comprises at least 50% solids. The slurry is formulated to be admixed into paint and coating compositions to promote TiO.sub.2 extension. The slurry includes a structured pigment, a coarse particle size pigment, and a fine particle size pigment. The structured pigment comprises about 20% to about 55% of the slurry by dry weight and has a median particle size diameter of about 0.7.mu. to about 6.0.mu.. The coarse particle size pigment preferably comprises about 20% to about 60% by weight of the slurry and has a median particle size diameter of about 3.0.mu. to about 10.0.mu.. The fine particle size pigment preferably comprises up to about 50% by dry weight of the slurry and has a median particle size diameter of about 0.2.mu. to about 1.0.mu..