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Calcium silicate: CaSiO3
Calcium silicate, made from the mineral wollastonite, has a needle-like structure, good brightness and relatively low oil absorption. It is suitable for use in oil house paints, flat and semi-gloss interior oil paints and in latex paints. The pH of about 99 provides a buffer action to hold latex paints on the alkaline side.
Synthetic calcium silicate is a hydrous calcium silicate produced by hydrothermal reaction of diatomaceous silica and lime. Particle shapes vary from "rounded" to needle-like. All grades have an average particle size between 1.6 and 3.8 microns, within the colloidal range. The better grades are white in colour. The pigment provides an extension of the properties of diatomaceous silica. Its extremely high oil absorption means very high flatting efficiency and high dry hiding effect. It also indicates use in a small proportion, about 10 per cent, of the total extender. Water absorption is exceptionally high and the producer especially recommends the pigment for latex paints.