There are two main ways of forming a colloid; reduction of larger particles to colloidal size or condensation of smaller particles, e.g. molecules, into colloidal particles. This latter generally makes use of chemical reactions such as hydrolysis or displacement. Laboratory and industrial methods make use of several techniques.This page gives a brief overview of some of these techniques, but it should be noted that there are a broad range used in practice.
A method of forming an aerosol is to tear away a liquid spray with a gas jet. The process can be helped by separating the liquid into droplets with electrostatic repulsions, done by applying a charge to the liquid.
Emulsions are usually prepared by vigorously shaking the two constituents together, often with the addition of an emulsifying agent, e.g. a surfactant such as soap, in order to stabilise the product formed.
Semi-solid colloids, known as gels, may be formed from the cooling of lyophilic sols that contain large linear molecules and have a much greater viscosity than the solvent.
Colloids are often purified by dialysis, a very slow process, where the aim is to remove a large part ot any ionic material that may have accompanied their formation. A membrane is selected that will not allow colloid particles through but will let the solvent and ions permeate through. The method relies on diffusion, osmosis and ultrafiltration.