Michael Faraday's gold colloids

These liquids are some of the first examples of metallic gold colloids, made by Michael Faraday over 150 years ago

  • Michael Faraday Gold Colloids sample

    Michael Faraday's Gold Colloids sample.

    Credit: Paul Wilkinson
  • Date

    1856
  • Place made

    Basement laboratory at the Ri

  • People

  • Materials

    Glass, gold, solutions

  • Measurements

    Varied

  • Key words

    Michael Faraday, gold, colloid, experiment, nanoscience

Description

These liquids are the first examples of metallic gold colloids. They were made, accidentally, by Michael Faraday whilst he was mounting thin sheets of gold leaf onto microscope slides.

Faraday spent a significant amount of time in the mid 1850s investigating the properties of light and matter. He made several hundred gold slides and examined them by shining light through them. To make the gold leaf thin enough to be transparent, however, Faraday had to use chemical means rather than mechanical (commercial gold leaf was made by hammering the metal into very thin sheets but this was too thick for his purposes).

Part of this process involved washing the films of gold, which Faraday noticed produced a faint ruby coloured fluid. He kept samples of the fluid in bottles and used them for similar experiments: shining a beam of light through the liquid. In his notebook Faraday observes: 

The cone was well defined in the fluid by the illuminated particles.

He realised that this cone effect was made because the fluid contained suspended gold particles that were too small to see with the scientific apparatus of the time but which scattered the light to the side. This is known as the Faraday-Tyndall effect, and it is because of this discovery that Faraday is seen as one of the first researchers into nanoscience and nanotechnology.

Interestingly, these colloids are still optically active: we can do exactly the same experiment as Faraday by shining a modern laser pointer through the bottle and producing a cone of light (see the photo below). Nobody knows why this is as we can’t unseal the bottles without damaging them but it’s very unusual: while most colloids last for a few months or even a year, Faraday's are now over 150 years old. 

More images

  • Laser shining through gold colloid

    Demonstrating the Faraday-Tyndall effect using a laser pointer

    Credit: Paul Wilkinson

  • gold colloid

    Gold colloids

    Credit: Paul Wilkinson

Where can I view this?

The colloids are on display in Faraday’s original laboratory on the Lower Ground Floor of the Royal Institution in the Faraday Museum.

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