Opalescence
Encyclopedia
Opalescence is a type of dichroism
seen in highly dispersed systems
with little opacity
. The material appears yellowish-red in transmitted light and blue in the scattered light perpendicular to the transmitted light. The phenomenon is named after the appearance of opal
s.
There are different degrees of opalescent behaviour. One can still see through a slightly opalescent phase. The more particles and the bigger the particles are, the stronger the scattering arising from them and the cloudier the particular phase will look. At a certain concentration the scattering is so strong that all light passing through is scattered, so that it is not transparent any more.
Examples are the blue sky
in the daytime and the yellowish-red sky at sunset. Another example can be made by adding a few droplets of milk to a glass of water. The liquid appears bluish but if one looks through the glass at a light source, it becomes yellowish-red. Opalescence is an effect exploited in lustreware pottery.
Dichroism
Dichroism has two related but distinct meanings in optics. A dichroic material is either one which causes visible light to be split up into distinct beams of different wavelengths , or one in which light rays having different polarizations are absorbed by different amounts.The original meaning of...
seen in highly dispersed systems
Colloid
A colloid is a substance microscopically dispersed evenly throughout another substance.A colloidal system consists of two separate phases: a dispersed phase and a continuous phase . A colloidal system may be solid, liquid, or gaseous.Many familiar substances are colloids, as shown in the chart below...
with little opacity
Opacity (optics)
Opacity is the measure of impenetrability to electromagnetic or other kinds of radiation, especially visible light. In radiative transfer, it describes the absorption and scattering of radiation in a medium, such as a plasma, dielectric, shielding material, glass, etc...
. The material appears yellowish-red in transmitted light and blue in the scattered light perpendicular to the transmitted light. The phenomenon is named after the appearance of opal
Opal
Opal is an amorphous form of silica related to quartz, a mineraloid form, not a mineral. 3% to 21% of the total weight is water, but the content is usually between 6% to 10%. It is deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock, being most...
s.
There are different degrees of opalescent behaviour. One can still see through a slightly opalescent phase. The more particles and the bigger the particles are, the stronger the scattering arising from them and the cloudier the particular phase will look. At a certain concentration the scattering is so strong that all light passing through is scattered, so that it is not transparent any more.
Examples are the blue sky
Diffuse sky radiation
Diffuse sky radiation is solar radiation reaching the Earth's surface after having been scattered from the direct solar beam by molecules or suspensoids in the atmosphere. It is also called skylight, diffuse skylight, or sky radiation and is the reason for changes in the colour of the sky...
in the daytime and the yellowish-red sky at sunset. Another example can be made by adding a few droplets of milk to a glass of water. The liquid appears bluish but if one looks through the glass at a light source, it becomes yellowish-red. Opalescence is an effect exploited in lustreware pottery.