How to determine the turbidity – in the coloring compounds
Turbidity – clarity of pigments is measured by light refractive index (refractive index) and size of colored particles.
1) The refractive index of a substance is the ability to deflect light when light shines on it. For white, the higher the index of refraction and the closer the particle size to the optimal size, the more opaque the color. White titanium pigment has the highest refractive index, so it is most opaque, then lead and zinc. However, when mixed with film oils with different refractive indices, one can turn opaque pigment into clear, because turbidity is now measured by the difference between the refractive index of the colored particles and the refractive index of the binder. sticky. Inorganic (non-carbon) pigments have a high refractive index, whereas organic (carbon-containing) pigments have a much lower refractive index, so inorganic colors are often opaque, whereas organic colors are often .
Below is the refractive index table of some colored particles and binders:
Film forming oils 1.4 – 1.6
Talc (magnesium silicate) 1.55
2.55 – 2.76
Calcium carbonate (plaster) Zinc Oxide (white zinc) Lead Carbonate (white lead) Titanium dioxide (white titanium)
The size of the color particles is also an important factor affecting the turbidity of the color. As the size of the color particle increases, the ability to scatter light of the color first increases, reaching a maximum at a certain size – called the optimal size. Then the ability to scatter light again decreases as the particle size continues to increase. So the turbidity of the first color increases with the particle size, reaches the maximum value (most opaque) at the optimal size, then decreases as the particle size gets larger.
Therefore, while it is not possible to change the index of color and binder, the manufacturer can also adjust turbidity – by changing the size of the particles.