A white powdered substance would be due to, what I assume, is the Tyndall effect, so has to do with the particle size, and not the identity of the substance.
12.
It is particularly applicable to colloidal mixtures and fine suspensions; for example, the Tyndall effect is used in nephelometers to determine the size and density of particles in aerosols and other colloidal matter ( see ultramicroscope and turbidimeter ).
13.
The brightness of the colours is neither the product of iridescence ( except in the American kingfishers ) or pigments, but is instead caused by the structure of the feathers, which causes scattering of blue light ( the Tyndall effect ).
14.
In a statistical sense, elastic scattering of light by numerous particles much smaller than the wavelength of the light is a process known as Rayleigh scattering while the similar process for scattering by particles that are similar or larger in wavelength is known as Mie scattering with the Tyndall effect being a commonly observed result.
15.
If the microstructures are spaced randomly, light of shorter wavelengths will be scattered preferentially to produce Tyndall effect colors : the blue of the sky ( Rayleigh scattering, caused by structures much smaller than the wavelength of light, in this case air molecules ), the luster of opals, and the blue of human irises.
16.
The Tyndall effect is seen when light-scattering particulate-matter is dispersed in an otherwise-light-transmitting medium, when the cross-section of an individual particulate is the range of roughly between 40 and 900 nanometers, i . e ., somewhat below or near the wavelength of visible light ( 400 750 nanometers ).
17.
While it shows up in the bottle, the amount of dye in one use of the gel is likely not enough to change the colour of the large quantity of bathwater, which I think gets its greenish-blue colour due to the Tyndall effect or Rayleigh scattering .-talk ) 15 : 50, 19 November 2008 ( UTC)
