Aluminum silicates (kaolin, china clay) are available in various sizes and are referred to as hydrous clays. The particle shape is lamellar, which contributes to film re-enforcement, reduction in porosity, and settling resistance. Calcining of clay removes the water of hydration and changes the structure from crystalline to nearly amorphous. The particle then appears more nodular and is widely used in flat and eggshell finish latex and alkyd paints in conjunction with titanium dioxide to improve opacity or “hiding power” of white paints.fig. (23)
Sodium Potassium Aluminum Silicate, also known as nephylene seyenite (trade name Minex) is a hard, nodular-shaped pigment that has found use in replacing amorphous silica pigments in tint bases and exterior coatings. The cleaner, brighter color of nephylene seyenite allows for better tint bases and pastel colors. The pigment is only slightly reactive in acids and shows excellent resistance to chalking, and improves scrubbability and burnish resistance in interior low sheen paints.fig. (25)
Silica is a hard, naturally occurring material that provides good burnishing resistance and wearing characteristics. However, Amphorous Silica is slowly being replaced by other extender pigments because of health concerns.
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