Tar is a thick, dark liquid produced by heating organic material in the absence of air, while pitch is the denser, more solid residue left behind when tar is further distilled or aged. The two terms are closely related and sometimes used interchangeably in casual speech, but they describe different stages of the same family of materials. Both have been essential to human civilization for tens of thousands of years, and the distinction between them still matters in industries ranging from aluminum smelting to road paving.
How Tar Is Made
Tar forms through a process called pyrolysis, which is just a technical way of saying “heating something until it breaks down without letting it catch fire.” When wood, coal, or petroleum is heated in a low-oxygen environment, the complex organic molecules inside begin to decompose. Some of those molecules escape as gases, some condense into oily liquids, and some remain as charcoal. The oily condensate is tar.
The source material determines the type of tar. Wood tar comes from burning or slowly cooking timber, particularly resinous species like pine. Coal tar is a byproduct of converting coal into coke for steelmaking. Petroleum tar derives from the refining and cracking of crude oil. Each type has a different chemical fingerprint, but all share the characteristic dark color, strong smell, and sticky consistency that most people associate with the word “tar.”
Wood tar production is ancient and straightforward. In its simplest form, you pile wood into a mound, cover it with earth to limit airflow, light it, and collect the dark liquid that seeps out. More controlled methods use kilns or retorts. Modern research into wood pyrolysis continues to examine how different conditions affect what comes out of the process, including the composition and behavior of the tar vapors produced.1Processes. Influence of Brown’s Gas on Cracking Behavior of Gas-Phase Tar during Pine Wood Pyrolysis
How Pitch Differs from Tar
Pitch is essentially tar with most of its lighter, more volatile components driven off. If you take tar and heat it further, or simply let it age and evaporate, the remaining material becomes progressively thicker and harder. At room temperature, pitch can appear completely solid. You can shatter it with a hammer. Yet given enough time, it flows like a liquid, just extraordinarily slowly.
The most famous demonstration of this property is the pitch drop experiment at the University of Queensland in Brisbane, set up in 1927 by Professor Thomas Parnell. A funnel of heated pitch was allowed to settle and then left to drip under gravity. Since then, only nine drops have fallen. The experiment illustrates that pitch behaves as a fluid with an almost unimaginably high viscosity, roughly 100 billion times thicker than water.2European Journal of Physics. The pitch drop experiment
This dual personality is what makes pitch useful. At high temperatures it softens and flows, allowing it to be shaped, poured, or used as a binder. When it cools, it hardens into a rigid, waterproof mass. Tar, by contrast, remains sticky and semi-liquid at ambient temperatures, which makes it better suited for coatings and impregnation rather than structural bonding. The rheological behavior of pitch has been studied extensively, and researchers have found that the softening point and viscosity of pitch are tightly linked, with viscosity dropping predictably as temperature rises toward roughly 180 °C.3Fuel. Influence of heat and pressure treatment on the rheological behavior of petroleum pitches Pitch also exhibits viscoelastic behavior, meaning it can store and release energy like a spring even while slowly flowing, a property that matters when pitch is used as a binding agent in high-performance materials.4Carbon. Determination of viscoelastic properties of pitches by torsional creep
Chemical Composition and Why Source Material Matters
Both tar and pitch are complex mixtures rather than single chemicals. They contain hundreds of individual compounds, many of them polycyclic aromatic hydrocarbons, or PAHs. These ring-shaped molecules are what give tar and pitch their dark color and are also the reason some forms are hazardous to health.
The source material changes the chemistry dramatically. Coal tar pitch, the kind most commonly used in heavy industry, contains higher amounts of aromatic compounds and PAHs compared to wood-derived alternatives.5PubMed Central. Effect of Sulfur on Wood Tar Biopitch as a Sustainable Replacement for Coal Tar Pitch Binders This makes coal tar pitch an excellent binder and conductor but also a bigger health and environmental concern. Wood tar tends to be chemically “cleaner,” with fewer of the most problematic PAHs, though it still contains enough to warrant caution.
Petroleum pitch sits somewhere in between. It is produced from the heavy residues of oil refining and can be engineered to have specific properties by adjusting the feedstock and processing conditions. Researchers have shown, for instance, that blending petroleum-derived materials with synthetic pitches changes the molecular structure and softening behavior of the result in predictable ways, which matters for manufacturing advanced carbon materials.6Energy & Fuels. Spinnable Mesophase Pitch Prepared via Co-carbonization of Fluid Catalytic Cracking Decant Oil and Synthetic Naphthalene Pitch
The Naval Stores Era
For centuries, tar and pitch were among the most strategically important materials in the world. Wooden ships needed constant waterproofing, and the combination of tar-soaked rope and pitch-sealed hulls kept navies afloat. The collective term for these products was “naval stores,” a category that also included turpentine and rosin, all derived from pine trees.7Treesearch. Naval stores: A history of an early industry created from the South’s forests
In practice, the difference between tar and pitch in shipbuilding was functional. Tar was applied as a preservative coating to rope and wood, soaking into the fibers and pores to repel water and resist rot. Pitch, being thicker and harder when cool, was used to seal seams between hull planks. Sailors would heat pitch until it flowed, pour it into the gaps, and let it set into a rigid, waterproof barrier. The phrase “pitch black” comes directly from the color of this material.
The naval stores industry was so important that European powers fought over access to pine forests. England depended heavily on tar and pitch imports from Scandinavia and the Baltic before turning to its American colonies, where vast longleaf pine forests in the southern regions became a major source. The industry dominated the economy of places like North Carolina well into the 19th century, only fading as iron and steel replaced wood in shipbuilding and petrochemicals offered synthetic alternatives.
Tar and Pitch in Prehistory
Human use of tar predates written history by a wide margin. Archaeologists have found birch bark tar used as an adhesive on stone tools dating back tens of thousands of years. Perhaps most striking is the evidence that Neanderthals produced birch tar using surprisingly sophisticated methods. Analysis of two exceptional tar pieces from Königsaue, Germany, dating to between 45,000 and 80,000 years ago, found that the tar was not made using the simplest possible technique. Instead, the Neanderthals distilled it in an intentionally created underground environment that restricted oxygen flow, a process that remained invisible during operation.8PubMed Central. Production method of the Königsaue birch tar documents cumulative culture in Neanderthals
The pieces themselves were small, weighing 1.35 grams and 0.83 grams, but the implications are large. Making tar underground requires understanding that you need to limit air to prevent the bark from simply burning, then collecting the resulting liquid and allowing it to accumulate. This is not a one-step process you stumble into accidentally. Researchers argue it points to cumulative cultural knowledge passed between generations, a cognitive ability once considered uniquely human.8PubMed Central. Production method of the Königsaue birch tar documents cumulative culture in Neanderthals
Medical Uses of Wood Tar
Pine tar has a long history in folk medicine, and it turns out some of that traditional use holds up under scrutiny. Topical pine tar preparations are still used to treat psoriasis, eczema, and other chronic skin conditions. The mechanism appears to involve reducing the rate at which skin cells divide, helping the skin return to a normal growth pattern. Pine tar also has anti-itch, anti-inflammatory, antibacterial, and antifungal properties.9PubMed Central. Topical pine tar: History, properties and use as a treatment for common skin conditions
If you have ever used a tar-based dandruff shampoo, you have encountered this application directly. These products contain refined coal tar or pine tar at low concentrations. The tar slows down the overproduction of skin cells on the scalp that causes flaking. The treatment is effective enough that tar preparations have remained in use despite the availability of newer alternatives, though the smell and staining can be off-putting.
It is worth noting that the medical use of tar is specifically controlled for dose and exposure. The same PAH compounds that make coal tar pitch hazardous in industrial settings are present in medical tar products, just at much lower concentrations and applied to the skin surface rather than inhaled. The safety profile of topical pine tar at therapeutic doses is generally considered acceptable, though regulatory attitudes have varied over the years across different countries.
Health Risks of Coal Tar Pitch
While pine tar on your scalp is one thing, breathing in coal tar pitch fumes in a factory is quite another. Coal tar pitch volatiles are classified as carcinogenic, and the evidence for this is strong. Workers exposed to high levels of these fumes, particularly in aluminum smelting, coking operations, and roofing, face elevated rates of lung and skin cancer.
Research on occupational exposure has estimated that over half of lung cancers among heavily exposed workers can be attributed to coal tar pitch volatiles at cumulative exposures above a certain threshold.10Occupational and Environmental Medicine. Compensating lung cancer patients occupationally exposed to coal tar pitch volatiles Animal studies have confirmed the mechanism, showing that coal tar pitch particles deposited in the respiratory system cause a progression from abnormal cell growth through precancerous changes to full carcinomas, with the severity directly related to the dose received.11Carcinogenesis. Investigation on the carcinogenic effects of coal tar pitch in rat respiratory tract by intratracheal instillations
The key distinction here is between coal tar products and wood tar products. Coal tar is far richer in the most dangerous PAHs, and the industrial processes that use coal tar pitch generate high-temperature fumes that workers inhale over years. Wood tar contains fewer of these compounds and is rarely encountered in the same high-exposure occupational settings. Petroleum pitch falls in between, with its hazard profile depending on its specific composition and processing history.
Environmental Concerns with Coal Tar Sealants
One of the more surprising environmental stories of the past two decades involves the coal tar sealants used on parking lots and driveways, primarily in eastern North America. These sealcoats contain high concentrations of PAHs that gradually wear off and wash into nearby waterways during rainstorms.
The environmental damage is measurable. Pavement samples from coal tar-sealed surfaces show consistently higher PAH levels than surfaces sealed with asphalt-based alternatives, and the PAH composition of any given pavement sample can be explained as a mixture of coal tar and bitumen in varying proportions.12PubMed. A source mixing model to apportion PAHs from coal tar and asphalt binders in street pavements and urban aquatic sediments When runoff from these surfaces reaches streams and ponds, it affects aquatic life. Laboratory studies have found clear negative relationships between the amount of coal tar sealant material and the health of freshwater invertebrate communities, with reductions in both abundance and species richness.13PubMed. Coal-tar based pavement sealant toxicity to freshwater macroinvertebrates
Fish are also vulnerable. Stormwater runoff from sealcoated asphalt has proven acutely lethal to juvenile coho salmon and causes cardiovascular abnormalities in developing zebrafish, with toxic effects persisting for months after the sealant is applied.14PubMed. Severe Coal Tar Sealcoat Runoff Toxicity to Fish Is Prevented by Bioretention Filtration A broader review of the literature has noted, however, that translating laboratory findings to real-world conditions is complicated by the dilution and interaction of runoff with natural stream materials like organic matter.15PubMed. A Review of the Literature on Potential Effects of Runoff from Refined Coal-Tar-Based Sealant Coating on Aquatic Organisms Still, several U.S. states and municipalities have banned or restricted coal tar-based sealants, and the trend is toward replacing them with lower-PAH alternatives.
Modern Industrial Applications
Despite the health and environmental concerns, pitch remains an irreplaceable material in certain industries, at least for now. Its most important modern use is as a binder in carbon anodes for aluminum smelting. The process of extracting aluminum from ore requires massive carbon electrodes, and coal tar pitch has traditionally been the glue that holds the carbon aggregate together in those electrodes. The pitch melts during mixing, coats the carbon particles, and then hardens into a solid mass when baked.
The aluminum industry uses large quantities of coal tar pitch for this purpose, and finding a replacement has been a persistent challenge. Researchers are actively investigating bio-pitch, made from wood tar and other biomass-derived sources, as a sustainable alternative. Early results are promising enough that bio-pitch is considered a legitimate contender, though matching the binding performance of coal tar pitch has required considerable effort in areas like adjusting the softening point and carbon yield of the bio-based material.16Next Materials. Current status and future potential of bio-pitch as binder in carbon anodes for aluminum production
Pitch also serves as the starting material for carbon fibers. When petroleum pitch is heated to around 420 °C for several hours, it forms a precursor that can be spun into fine filaments and then carbonized at 1,000 °C to produce carbon fibers with useful mechanical properties. Researchers have achieved tensile strengths of 650 MPa with pitch-based carbon fibers, which puts them in a useful range for structural and industrial applications, though they differ in character from the more commonly known fibers made from a polymer called polyacrylonitrile.17New Carbon Materials. Preparation and characterization of pitch-based carbon fibers Pitch-based fibers tend to have higher thermal conductivity and stiffness, making them valuable in aerospace and thermal management applications where those properties matter more than raw tensile strength.
Common Confusions Between Tar, Pitch, Asphalt, and Bitumen
One of the biggest sources of confusion is the overlap between tar, pitch, asphalt, and bitumen. In everyday English, people often use “tar” to describe the black stuff on a road, but modern road surfaces are almost never made with actual tar. They use asphalt, which is a mixture of aggregate (gravel and sand) bound together with bitumen, a naturally occurring or petroleum-derived material. Bitumen and tar look similar but have different origins: bitumen comes from crude oil or natural deposits and was never “cooked” from wood or coal, while tar is specifically the product of pyrolysis.
The terminology gets messier across different English-speaking countries. In British English, “bitumen” refers to the petroleum binder, while “asphalt” can mean either the binder or the finished road surface. In American English, “asphalt” usually means the finished pavement, and the binder might be called “asphalt cement.” Meanwhile, “tar” gets used colloquially for all of the above, which is how we ended up calling road surfaces “tarmac” even though genuine tar macadam has been rare for decades.
The confusion has practical consequences. When environmental researchers study PAH contamination in road materials, distinguishing between coal tar-based and bitumen-based sealants matters enormously, because the PAH content differs by orders of magnitude. A parking lot sealed with coal tar products can be a significant source of water pollution; the same lot sealed with asphalt-based products poses far less risk. Calling both materials “tar” obscures this critical difference.
Why Pitch-Based Products Are Hard to Replace
Given the health and environmental drawbacks, you might wonder why industries do not simply switch away from coal tar pitch. The short answer is performance. Coal tar pitch has a particular combination of properties, including high carbon yield when baked, good wetting of carbon surfaces, appropriate viscosity at mixing temperatures, and the ability to form a strong coke structure, that has proven difficult to replicate with other materials.
Bio-pitch from wood tar is the most promising substitute in aluminum production, but wood tar contains different molecular structures than coal tar. Coal tar pitch is rich in large aromatic ring systems that stack together neatly and carbonize efficiently. Wood tar contains more oxygen-containing compounds and smaller ring structures, which behave differently during baking. Researchers have found that adding sulfur to wood tar biopitch can modify its properties to move closer to the coal tar benchmark, but the chemistry is complex and the optimization is ongoing.5PubMed Central. Effect of Sulfur on Wood Tar Biopitch as a Sustainable Replacement for Coal Tar Pitch Binders
Petroleum pitch offers another path. Its molecular composition can be tailored more precisely than wood-derived alternatives, and the petroleum industry already produces the heavy residues needed as feedstock. The challenge is that petroleum pitch production depends on refinery operations that are themselves under pressure from the energy transition. As the world moves away from fossil fuels, the supply of the heavy residues used to make petroleum pitch may shrink, creating its own set of problems for industries that depend on pitch-based materials.
For carbon fiber production, pitch and polymer-based routes serve somewhat different markets. Pitch-based fibers excel in applications demanding high thermal conductivity or high modulus, while polymer-based fibers dominate where tensile strength and cost matter most. The two are more complementary than competitive, and pitch-based carbon fiber production is likely to remain a specialized niche even as the broader carbon fiber market grows.