• In physical and colloid chemistry, true colloidal particles range in diameter between 1 nanometer (10^-9 m) and 200 nanometers (or up to 1000 nm).
• Expressed in millimeters (mm), 200 nanometers equals 0.2 micrometers (um), which corresponds exactly to 0.0002 mm (2 x 10^-4 mm).
• While the upper boundary for soil clay separates in mechanical analysis is 0.002 mm (2 um), the true colloidal fraction within clay has an upper size limit of 0.0002 mm (0.2 um).
• Hence, 0.0002 mm represents the scientifically accepted upper size threshold for colloidal particles.

The scattering of light by colloidal particles that makes their illuminated path visible is known as the Tyndall effect.

• Brownian movement: The continuous random zigzag kinetic motion of colloidal particles caused by unequal collisions with dispersing solvent molecules.
• Tyndall effect: The optical phenomenon where colloidal particles scatter a focused beam of light, causing the path of the beam to become luminous and distinct.
• Flocculation: The coagulation or clumping together of dispersed colloidal particles into larger aggregates.
• Cataphoresis: The electrophoretic movement of positively charged colloidal particles toward the cathode under an applied electric gradient.