Page 38 - Curriculum Visions Dynamic Book

Chromium colours
Chromium compounds are mainly brightly coloured. As a result, they are widely used as the colouring agent, or pigment, in paints, glazes, glass and enamels.
The most common colours for chromium compounds are green, yellow and orange.
Glaze
An important use of coloured chrome oxide is to colour glaze. A glaze is a mixture of colouring powder and powdered glass in water. The article to be glazed is then dipped in the mixture, or it may be sprayed or brushed on.
The article is then fired so that the glass melts and forms a surface glaze.
 Chromate yellow
The bright yellow solution in the test tube is potassium chromate.
Also...
Paint manufacturers are among the main users of chromium compounds. A paint must protect the surface to which it is applied and also provide a pleasing and decorative colour. It must be easy to apply, make a thin even coating, and then dry quickly and uniformly.
Every paint is made of two parts, a powder of solid particles that gives the colour and also makes the paint opaque. This is known as the pigment. The pigment is mixed into a liquid, called the binder, that allows the pigment to be spread evenly over the surface.
In some cases the binder is made from
a solvent such as those based on petroleum. When applied, this evaporates and leaves
a deposit of the pigment on the surface.
At the same time the binder reacts with oxygen of the air, becoming a non-sticky solid.
In many more cases, modern paints are being made with a water base, for environmental reasons. However, pigments like chromium compounds, do not easily mix with water and must be added already wrapped in their binder. This suspension of particles is called an emulsion.
 A diagrammatic representation of potassium chromate – K2CrO4.
Oxygen
Potassium
Chromium
 Potassium dichromate
The striking orange compound
in this test tube has been used
as a tracer for finding out the route taken by water supplies.
 A diagrammatic representation of potassium dichromate – K2Cr2O7.
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