Soot has been put to use for thousands of years, from ancient Chinese ink-making to modern tire manufacturing. Today, most soot is refined into an industrial product called carbon black, and global production reaches about 15 million metric tons per year. The vast majority of that goes into rubber products, but soot and its derivatives also show up in inks, coatings, electronics, cosmetics, and energy storage.
Soot vs. Carbon Black
Raw soot and industrial carbon black are related but not identical. Carbon black is more than 97% pure elemental carbon, with less than 1% organic compounds and less than 1% inorganic ash on its surface. Raw soot, by contrast, can contain less than 60% carbon by mass, with significantly higher levels of ash and organic residues. The difference matters because carbon black’s extreme purity and controlled particle size make it suitable for precision manufacturing, while raw soot’s variable composition limits its industrial applications.
When people talk about “what soot is used for” in a modern context, they’re almost always talking about carbon black: soot that has been produced under controlled conditions to achieve specific particle sizes, shapes, and surface chemistry.
Tires and Rubber Products
This is the single largest use. Roughly 73% of all carbon black produced worldwide goes into automobile tires, with another 20% going into non-tire rubber goods like hoses, belts, gaskets, and shoe soles. That means 93% of the world’s carbon black ends up in some form of rubber.
Adding carbon black to rubber dramatically improves its tensile strength, tear resistance, and abrasion resistance. It also increases both static and dynamic stiffness. Without it, a tire would wear out far faster and offer less grip. The exact mechanism behind this reinforcement is still debated. Some researchers believe carbon black particles bond chemically to the rubber polymer chains during mixing and curing, while others argue the interaction is purely physical adsorption. A 1957 paper noted this disagreement, and more than six decades later, scientists still haven’t fully settled it. What everyone agrees on is that it works: carbon black is the original polymer nanocomposite, and no widely available substitute matches its combination of performance and cost.
Inks, Paints, and Coatings
Carbon black is one of the most stable black pigments available. It absorbs nearly all visible light, resists fading from UV exposure, and disperses well in liquid carriers. These properties make it a go-to ingredient in printing inks (including newspaper, packaging, and laser printer toner), automotive paints, and industrial coatings. About 7% of global carbon black production goes to these non-rubber applications, split among paints, coatings, inks, and plastics compounding.
In plastics, carbon black does double duty. It provides deep, consistent color, and it also shields the plastic from ultraviolet degradation. Black plastic pipes, garbage bags, and automotive trim all rely on carbon black to hold up in sunlight without becoming brittle.
Ancient Ink-Making
Long before industrial carbon black existed, soot was the foundation of writing ink across much of the world. In China, ink sticks were made by combining soot with animal glue and other additives, then pressing the mixture into solid form. Two main types existed: pine-soot ink, made from the incomplete burning of pine branches, and oil-soot ink, made from burning oils and fats.
The process required remarkable craftsmanship. Ancient ink makers managed to produce soot particles at the nanometer scale, a feat that depended on careful selection of raw materials and controlled firing in closed kilns (either flat or vertical designs). By the Han Dynasty, around 2,000 years ago, artisans already knew which regions produced the finest pine wood for soot. Government officials received monthly allotments of ink sticks made from pine sourced in what is now Qianyang, Shaanxi Province. The resulting inks were prized for calligraphy and painting, and the tradition of handmade ink sticks persists in East Asian art today.
Electronics and Anti-Static Protection
Carbon black conducts electricity, which makes it valuable in applications that have nothing to do with color. When carbon black particles with large enough aggregate structures are dispersed into an otherwise insulating polymer above a certain concentration threshold, the composite becomes electrically conductive. This property is exploited in several ways:
- Anti-static packaging: The plastic trays and bags used to ship computer chips and circuit boards contain carbon black to prevent static discharge from damaging sensitive components.
- Electromagnetic shielding: Carbon black-filled composites can block electromagnetic interference in electronic housings.
- Conductive adhesives and sensors: Specialized glues and sensing devices use carbon black to carry electrical signals through polymer matrices.
- Battery electrodes: Carbon black serves as a conductive additive in lithium-ion battery electrodes, helping electrons flow between the active material and the current collector.
Researchers are also exploring sustainable alternatives, such as biochar derived from lignin (a plant-based byproduct), as a replacement for petroleum-based carbon black in some of these energy storage roles.
Cosmetics and Kohl
Soot has been used in eye cosmetics for millennia. Kohl (also called kajal or surma) is one of the oldest cosmetic preparations in the world, and homemade versions are still widely used. In surveys of traditional preparation methods, about 80% of users made their own kohl at home by collecting soot from the flame of an oil lamp and mixing it with oil or eye ointment.
The safety picture is complicated. Traditional homemade kohl made purely from lamp soot is a simple carbon-based product. But commercially produced kohl often contains lead-based compounds like galena (lead sulfide) and minium (lead oxide), alongside amorphous carbon, magnetite, and zinc oxide. Prolonged use of lead-containing kohl has been linked to excess lead accumulation in the body, with potential effects on the brain and bone marrow. The U.S. FDA does not permit kohl in cosmetics or any other regulated product. In modern Western cosmetics, purified carbon black (with strict limits on impurities) is used as a pigment in eyeliners, mascaras, and other products under regulated conditions.
Health Risks of Soot Exposure
While refined carbon black is considered relatively safe for consumer products at controlled levels, occupational exposure to raw soot carries serious health risks. The International Agency for Research on Cancer classifies soot, specifically as encountered in the occupational exposure of chimney sweeps, as a confirmed human carcinogen. There is sufficient evidence linking soot exposure to lung cancer and non-melanoma skin cancer, and limited evidence connecting it to bladder cancer.
These risks apply primarily to people who breathe in or have prolonged skin contact with unrefined soot over months or years, such as chimney sweeps, firefighters, and industrial workers. The cancer connection was actually one of the earliest occupational health discoveries in history: in 1775, a London surgeon identified scrotal cancer in chimney sweeps and traced it to chronic soot exposure. For everyday consumers, soot-derived products like tires, printer ink, and cosmetics contain carbon black that has been processed to minimize harmful compounds on its surface.