What is a pigment?
A pigment is a particulate material used to color and opacify a coating or film – which may be a paint, an ink, a sheet of plastic or paper, a ceramic glaze, a tablet coating, a fabric and many other forms of coating.
A pigment should be:
- Insoluble in the coating, plastic, paper or any other binder system it is used in
- Chemically inert and non toxic
- Heat and light stable
- As pure and consistent as possible to produce even coloration and prevent cross contamination
The most significant difference of a pigment to a dye is that the latter may be soluble in some applications.
Typical examples of pigments include
- natural earth colors such as iron oxides and their synthetic analogues
- complex organic compounds such as phthalocyanine blues and greens
- and titanium dioxide!
It is generally accepted that a pigment will provide significant opacity whereas cheaper particulate fillers and extenders may be virtually transparent in the end application due to their lower refractive index, although they often provide functional properties such as viscosity and flow control. The latter are usually natural products such as calcium carbonate (ground chalk), clay, talc etc.
Some compounds such as synthetic silica (SiO2) meet the first four criteria for pigments but are virtually transparent in a binder system and are used for specific application properties.
Titanium dioxide pigment
Commercial titanium dioxide is a synthetic pigment, not pure ‘chemical’ TiO2.
There are many different TiO2 pigments, with each manufacturer offering a range of products tailored to specific applications or range of applications. Although consistency in chemical composition is important in a TiO2 pigment, every product is designed and manufactured to have certain characteristics.
Individual titanium dioxide products are manufactured to yield maximum opacity, the best possible color, easy dispersion, good stability, high gloss (or ‘flatness’ where required!), and the required level of durability and color or light stability for the end application.
The base pigment particle, in one of two crystal forms, is manufactured to a very closely controlled particle size distribution, and then usually coated with a combination of inorganic and organic surface treatments to develop specific characteristics.
Because of its clean white color and tone titanium dioxide pigment is used in virtually every white, pastel and many colored items in everyday use.
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