Pigments

Pigments

Definition
Pigments are the substances which are used to give the proper colour to paints.
Types of Pigments
Lead forms various types of pigments. Some of them are given below.
1. White lead Pigment
2. Red lead Pigment
3. Chrome Yellow Pigment
4. Chrome Red Pigment
5. Turner’s Yellow Pigment
1. White Lead Pigment
White lead Pigment is a basic lead carbonate.
Molecular Formula
[2PbCO3. Pb(OH)2] or [Pb3(OH)2.(CO3)2]
Colour
This lead pigment is white in colour.
Properties
The white colour gradually darken due to the formation of Pbs with Atmospheric H2S. It is also poisonous.
2. Red Lead Pigment (Sandhur)
Molecular Formula
Pb3O4 – Triplumbic Tetra Oxide
2PbO.PbO2 – Lead-Sesqui Oxide
Colour
It is used as red coloured pigment, which varies from orange red to brick red dur to particle size and impurities.
Properties
It is soluble in water but soluble in acids.
3. Chrome Yellow Pigment
Molecular Formula
PbCrO4 – Lead Chromate
It occurs in nature as crocoite.
Colour
It is used as yellow coloured pigment.
Properties
It is insoluble in water but soluble in nitric acid and caustic alkalis.
4. Chrome Red Pigment
Molecular Formula
PbCrO4.PbO – Basic Lead Chromate
Pb2CrO5 – Basic Lead Chromate
Colour
It is used as dark red pigment in paints.
5. Truner’s Yellow Pigment
Molecular Formula
PbCl2.4PbO
Other Pigments
Except above pigments, yellow lead monoxide (massicot) and red lead monoxide (litharge or Murda-sang) are also used in paints.