The Tyndall Effect: The Proof of Light for True Colloids

Direct a fine beam of light — ideally a green laser — through a true colloidal solution, and the beam becomes visible in the water as a glowing band. In pure water or an ionic solution, the light passes through without a trace. The reason: colloidal particles are large enough to scatter light; dissolved ions and water molecules are not.

The effect is named after the Irish physicist John Tyndall, who studied light scattering by the finest particles in the 19th century. It is the same physics that makes sunbeams visible in morning mist.

The Tyndall effect proves that colloidal particles are suspended in the solution at all. That makes it the fastest test of authenticity. About concentration it says only so much: colour is the better guide there, for it deepens as the content rises. Still, a clean, even band of light without streaks or visible flakes is a good sign of a stable, finely dispersed solution.

Here, a look through the laser light is part of every batch, together with the inspection of colour and clarity. What we bottle has passed these tests.

Beyond the band of light there is a second proof anyone can perform with the naked eye: colour. True metal nanoparticles resonate with light — physicists call this plasmon resonance. That is why true colloidal gold glows deep ruby red and true colloidal silver a warm golden yellow to brownish. A water-clear liquid calling itself “colloidal gold” contains no gold particles — at best dissolved ions.

The colour even betrays particle size: the finest gold particles colour the solution red, larger ones shift the tone towards violet — the same physics that made the Romans’ Lycurgus Cup glow.