Chemistry... now in colour
Colours are part of our everyday lives, directly influencing how we perceive our surroundings, our choices and even our appetite. The blue of the sky, the white of a whitewashed wall or the bright red of a ripe cherry are not just visual details; they are manifestations of a fascinating science: chemistry. But have you ever stopped to think about how colours arise and why we see a particular shade?
How do we see colour?
To understand how we see colours, we need to investigate a little further into the interaction between light and the human eye. Colour perception begins when light enters our eyes and is captured by specialised cells called cones, located in the retina. Each type of cone responds to three different wavelengths (short, medium and long, which in terms of colours correspond to the blue, green and red spectrum), allowing us to distinguish millions of shades. However, colour does not reside in objects themselves, but is the result of the interaction between light and the molecules of those objects. Each molecule has a specific chemical signature, determining which colours are absorbed and which are reflected.
For example, imagine you are looking at a strawberry. The molecules in the strawberry's skin absorb most of the green and blue, but not the red, which is reflected. This is precisely why we see the strawberry in that shade. A black object absorbs almost all light, while a white object reflects almost all the light it receives.
From the laboratory to our everyday lives
Historically, dyes and pigments were extracted from natural sources such as plants, minerals, animals and even some metals. However, these sources had limitations in terms of availability, colour stability and the range of colours that could be obtained.
The revolution came in the 19th century with the synthesis of artificial dyes. In 1856, while trying to synthesise quinine in the laboratory, the young chemist William Perkin accidentally discovered mauveine, or aniline purple, the first synthetic dye. This discovery paved the way for an entire synthetic dye industry, offering a wider colour palette, greater durability and resistance and, not least, lower production costs.
Since then, advanced pigments have emerged, such as those based on iron oxides, recognised for their stability and extreme resistance to UV rays, rain, pollution and high temperatures, making them essential in paints for the automotive industry and architectural coatings, for example.
Another significant advance was the introduction of nitrocellulose paints in 1921, which ensured increased adhesion to surfaces, easy application and very fast drying, as well as being much more resistant to weathering. From the 1950s onwards, acrylic enamels and water-based coatings appeared, reducing the emission of volatile organic compounds (VOCs). Depending on their composition, these components can have harmful side effects on human health (they are carcinogenic) and cause photochemical reactions that contribute to the formation of tropospheric ozone.
Today, modern chemistry continues to innovate with advanced protective coatings, such as solvent-free powder coatings, which offer durable protection with a lower environmental impact.
The colours of sustainability
The chemistry of colours exists in a delicate balance between the need to create pigments and dyes that are stable and resistant to the elements, but which are also environmentally sustainable. Many traditional products still have a high environmental impact, either because of the raw materials used or because of the waste and emissions generated during their production.
The chemical industry's response has been to develop more environmentally friendly alternatives using renewable raw materials such as agricultural waste, algae and various plant extracts (such as grape skins). These natural materials, combined with biodegradable binders such as gum arabic or vegetable oils, make it possible to create products that are safe for the environment and human health. In addition to drastically reducing VOC emissions, natural inks are also less harmful to indoor air quality. Opting for this eco-friendly approach also makes it possible to valorise renewable resources (such as organic waste) and support local economies through the use of regional raw materials, contributing significantly to a circular economy.
The chemical industry is also investing in innovative materials, such as new semi-transparent polyamides, which combine durability, chemical resistance and colour stability in difficult environmental conditions, reducing the need for frequent replacements and cutting down on waste.
A bright and colourful future
Another notable advance is structural colour. Thanks to work at the nano and microstructure level, it is possible to produce colour through the reflection rather than absorption of light. This innovation not only eliminates harmful substances, but also drastically reduces the heat absorbed by buildings or vehicles, contributing to energy efficiency and the fight against global warming.
This colour creation process still needs to be simplified and scaled up to reduce costs and meet mass production requirements. But the advantages are clear, as inks based on this method are much more efficient (less quantity is needed to paint the same area), do not fade over time, absorb less heat, are non-toxic and contribute to reducing carbon emissions in production and waste management.
Another avenue being explored is the creation of the next generation of pigments and colours from plant cellulose. Conventional substances used to make our cosmetics, fabrics, paints and packaging more colourful often include metallic ingredients or petroleum derivatives. For example, titanium dioxide (TiO2) is widely used to produce white, but by studying the Cyphochilus beetle (which is completely white), scientists have mimicked the nano-structure inside the beetle's exoskeleton (which reflects only white light) and replicated it in a chain of cellulose molecules.
Chemistry, the ubiquitous ally
From understanding light and the receptors in our eyes to developing advanced and sustainable pigments and dyes, colour chemistry is fundamental to how we perceive our visual “universe” and plays an essential role in environmental sustainability.
From the historic discoveries of Isaac Newton and William Perkin to modern innovations in the field of colour and inks, chemistry continues to contribute to making the world more environmentally conscious and, of course, much more fun.
