Important properties of pigments

Not all colored insoluble products synthesized are commercial pigments. To qualify as a pigment, a product needs to demonstrate various characteristics that are not covered in the definition alone, but are important from an application standpoint. Some important properties and characteristics of pigments are briefly discussed below. 

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An important property of a pigment is its ability to maintain its color when exposed to light, weather, heat, and chemicals. This property is seldom measured for pigments alone. Rather it is determined for the dispersion of a pigment in a desired medium, eg, paints or plastics, and in many cases it is compared to the performance of a standard pigment. The observed changes are the result of complex pigment and media reactions and their possible interactions. In aH evaluations, time of exposure plays a role. 

This section will discuss some important concepts from coloristic practice and the optical properties of pigmented systems. Space considerations permit a treatment of only the most vital concepts. The reader must consult the literature for further details and accounts of special problems [1], A review on the effect of crystal structure on color application properties was published [2],... 

One of the important properties of porphyrins is that they complex with divalent metals, the pyrrole nitrogens being ideally spaced to allow this. Of vital importance to life processes are the porphyrin derivatives chlorophyll and haem. Chlorophyll (actually a mixture of structurally similar porphyrins chlorophyll a is shown) contains magnesium, and is, of course, the light-gathering pigment in plants that permits photosynthesis. 

Other important properties of Cr02 when used as a magnetic pigment are its black color, electrical conductivity (2.5-400 O-1 cm-1 [5.27]) and relatively high crystal hardness (Mohs hardness 8-9 [5.20]). Therefore, coating formulations based on Cr02 require less or even no additives such as carbon black (good conductivity, black color) or refractory oxides such as alumina. 

All commercial bismuth vanadate pigments are based on pure bismuth vanadate with monoclinic or tetragonal structure. The most important properties of all bismuth vanadate pigments are... 

In general the following properties of pigments are important in selecting a pigment for any particular product ... 

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