Colorants mica flakes

The hard rock deposits are mined mainly for feldspar with mica and quartz being accessory minerals. These deposits are extensive, often covering hundreds of square meters and are recognized by the light-colored, granite-like appearance with shiny mica flakes being a prominent feature. The mica content of these deposits ranges from approximately 6—10 wt %. 

Interference pigments n. Materials used as pigments, which depend on the interference of light for their color. They are generally made from platelets coated with a thin film of higher refractive index. For example, thin films of titanium dioxide coated on mica flakes are one type manufactured and used today. 

Pearlescent pigments contain small flakes or platelets of the mineral mica that are additionally coated with a very thin layer of titanium dioxide. The simultaneous reflection of light from many layers of small platelets creates an impression of luster and sheen. By varying the thickness of the coating on the surface of the mica particles, pigment manufacturers can achieve a range of colors for the pearlescent effect. 

In practice, platelet crystals are synthesized with a layer thickness d calculated to produce the desired interference colors (iridescence) [5.206], [5.207], Most nacreous pigments now consist of at least three layers of two materials with different refractive indices (Fig. 73). Thin flakes (thickness ca. 500 nm) of a material with a low refractive index (mica) are coated with a highly refractive metal oxide (e.g., Ti02, layer thickness ca. 50-150 nm). This results in particles with four interfaces that constitute a more complicated but still predictable thin film system. The behavior of more... 

On the other hand, new pigments based on transparent silica flakes show extremely strong optical effects, which are different to mica pigments [5.244]. Angle dependent colors and other effects, achieved by the combination of these Si02-flakes with... 

Green mica Aventurine Green, massive, bright luster and color due to inclusions of small, shiny flakes of chrome-rich mica... 

Improved color strength and very high luster are produced by the combination of precise thickness silica flake substrate materials, selected for their interference chro-maticity, and by deposition of titania or iron oxide coating layers of the precise thickness required to generate the same interference color. These pearl luster pigments show stronger chromaticity L a b -values than can be produced with mica-based designs. 

Pearlescent pigments based on controlling the physical form of the colorant as thin, transparent flakes can be employed in plastisols and for flakes of mica, in rigid formulations (66,67). These pigments are similar to metallics in their sensitivity to shear-induced fiacture. 

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