Scottish science · Light and colour
James Clerk Maxwell explained light as an electromagnetic wave and helped establish the three-colour method of photography. These were two related investigations into light: one asked what light is; the other asked how its colours could be recorded and reconstructed. The famous tartan-ribbon demonstration of 1861 joined Maxwell’s colour research with the photographic work of Thomas Sutton, who made the exposures.
The useful distinction: Maxwell developed a scientific theory with enormous technological consequences. His contribution to radio and wireless communication was the underlying physics; the transmitters, receivers and communication systems came through later experimental and engineering work.
What changed when light became electromagnetic?
An electric or magnetic field describes an influence throughout a region of space. A compass responding to a nearby magnet is a familiar way to notice one. Before Maxwell, experiments had already established connections between electricity and magnetism. Michael Faraday’s work on induction showed how a changing magnetic situation could produce an electrical effect.
Maxwell’s theory made the relationships mathematically consistent and showed that coupled electric and magnetic disturbances could travel as waves. The calculated speed was strikingly close to the measured speed of light. That agreement supported a profound conclusion: light belonged to the same physical system as electricity and magnetism.
His paper A Dynamical Theory of the Electromagnetic Field was read to the Royal Society on 8 December 1864 and published in 1865. Both dates appear in accounts of the achievement because they refer to different stages of the paper’s history.
Radio waves and visible light now sit within one electromagnetic spectrum. They differ in frequency and wavelength, rather than requiring unrelated explanations. NASA’s guide to electromagnetic waves follows the connection from Maxwell’s theory to Heinrich Hertz’s later radio-wave experiments.
How could black-and-white photographs produce colour?
The other puzzle was practical: a photographic plate could record brightness, but how could it preserve information about colour? Maxwell’s approach separated the information into channels. Photograph the same subject through different coloured filters, then use corresponding coloured light to reconstruct the image.
For the demonstration at the Royal Institution in London on 17 May 1861, Sutton photographed a ribbon through filters. Three monochrome images, associated with red, green and blue-violet, were projected through corresponding filters and brought together on a screen. Maxwell supplied the scientific argument and presentation; Sutton supplied the photographic work.
One scene → three records → one colour image
Each channel records how strongly the scene appears through its filter. The photographic record itself is monochrome.
Record through a red filter. Project the resulting positive image with red light.
Record through a green filter. Project the positive image with green light.
Record through a blue-violet filter. Project the positive image with blue-violet light.
Worked example: making yellow. In an ideal three-colour system, a yellow area can be reconstructed using red and green light together, with little blue. A separate yellow projector is unnecessary.
This is additive colour: coloured light is combined. It differs from mixing paints or printing inks, which absorb parts of the light falling on them. A screen uses the additive principle when it varies its red, green and blue components. Suitable mixtures can reproduce a wide range of colour appearances; three fixed primaries do not reproduce every colour the eye can perceive.
There is a second lesson hidden in the diagram. All three images must line up. If the subject moves between exposures, or the projected images are misaligned, the channels disagree about where an edge belongs. Colour fringes appear. A stationary ribbon was a much easier subject for this method than a moving person.
Why the “first colour photograph” needs a careful caption
The ribbon is widely celebrated as the first durable three-colour photographic image. But the 1861 demonstration was a projected combination of separate records, and its colour was imperfect. The photographic materials then available responded poorly to red and green light. Maxwell himself recognised that more suitable materials were needed.
There is also a date distinction worth checking whenever you see the familiar picture. The National Science and Media Museum identifies its colour print as a 1937 Vivex print made from the original negatives. A later print can preserve an important experiment’s imagery without being a paper photograph produced in 1861. Giving Sutton credit and distinguishing exposure, projection and later printing makes the story more interesting and more accurate.
An Edinburgh beginning, a wider scientific career
Maxwell was born in Edinburgh in 1831 and grew up at Glenlair in what is now Dumfries and Galloway. His education took him through Edinburgh and Cambridge; his academic work included Aberdeen, King’s College London and Cambridge’s Cavendish Laboratory. The James Clerk Maxwell Foundation connects these places with his life and research.
Those journeys are part of the Scottish story. His achievements developed through teaching, correspondence, experimental results and collaboration across institutions. The tartan ribbon offers an especially memorable image of that history, but the strength of Maxwell’s work lies in the questions it allowed other people to answer.
Two questions readers often ask
Did Maxwell write the four equations exactly as they appear today?
The familiar compact vector form came through later reformulation, especially by Oliver Heaviside. Maxwell’s original presentation was more extensive. The name recognises Maxwell’s foundational theory, while the notation also carries the work of later physicists and mathematicians. A Royal Society research paper available through Durham University explains that development.
Did Maxwell personally take the tartan photographs?
Thomas Sutton made the photographic exposures for Maxwell’s demonstration. “Maxwell and Sutton’s tartan-ribbon experiment” is a useful short description because it keeps both the theory and the photographic craft in view.
Keep exploring Scotland’s scientific history. Our Scottish inventions guide places Maxwell alongside other discoveries and practical innovations.
For a gift connected with your own Scottish family story, browse the Scottish heritage collection and choose a name or design that matters to the recipient.