Tree pitch is a thick, sticky, and highly aromatic natural exudate from trees. It is often confused with tree sap because both substances can be found seeping from the bark. However, pitch is chemically distinct from sap, which is a watery, sugar-rich fluid that circulates within the tree’s vascular system. The sticky material encountered on the exterior of a coniferous tree is actually resin, which is the primary component of pitch.
The Tree’s Natural Defense System
The production of tree resin is a localized biological response functioning as a mechanism for self-repair and defense. When a tree sustains a physical injury, such as a broken branch or insect boring, it immediately initiates a flow of resin. This substance acts as a physical sealant, quickly hardening upon exposure to the air to form a protective barrier over the wound.
This sealing action prevents the tree’s internal moisture from evaporating, which is known as desiccation. The resin’s composition also defends against pathogens like fungi and bacteria that might colonize the exposed tissue. Furthermore, the aromatic, volatile compounds in the resin are toxic to many insect pests, deterring them or trapping smaller invaders in the sticky substance.
Understanding Resin, Sap, and Pitch
The distinction between sap, resin, and pitch lies in their composition, function, and location. Sap is a water-based solution containing sugars and nutrients that flows through the vascular tissues (xylem and phloem) to transport resources. It is relatively thin and clear, and it is the substance harvested to make maple syrup.
Resin is a complex mixture of non-polar, hydrocarbon compounds, primarily composed of terpenes. These volatile organic compounds give the resin its strong, distinctive scent. Resin is produced and stored in specialized resin ducts, separate from the water-conducting system, and is deployed only in response to damage.
Pitch is often used interchangeably with resin, but technically, pitch refers to the processed or aged form of the material. Historically, pitch was created by heating pine resin to drive off the volatile turpentine fraction. This process resulted in a thicker, darker, and more durable substance. Therefore, the sticky substance oozing from a pine tree is chemically a resin, while “pitch” refers to the highly thickened or commercially refined product.
Historical and Modern Uses
Humans have utilized tree pitch and its derivatives for thousands of years due to its waterproof and adhesive nature. Historically, pitch was a fundamental material in naval construction, used for waterproofing the seams of wooden ships and boats. This application involved heating the material and applying it as a tar-like sealant to prevent water intrusion.
The industrial processing of resin yields two commercial products: turpentine and rosin. Turpentine is the liquid, volatile fraction used today as a solvent, paint thinner, and source for synthetic organic compounds. Rosin is the solid, non-volatile residue used in manufacturing adhesives, printing inks, varnishes, and sizing for paper.
Practical Cleanup Methods
The sticky nature of pitch makes it difficult to remove from skin, clothing, and vehicle surfaces. Since pitch is a non-polar, hydrocarbon-based substance, it resists water and requires a non-polar solvent for dissolution. Simple oil-based household substances are effective, such as mineral oil, vegetable oil, or peanut butter, as the fats break down the pitch’s chemical structure.
For surfaces like car paint or hardened pitch on hands, rubbing alcohol (isopropyl alcohol) is the most recommended solvent. Its chemical structure helps dissolve the resinous bond without damaging the surface. Apply a small amount of the solvent to the pitch and allow it to penetrate for a few minutes before gently wiping it away. Avoid harsh scraping with sharp tools, which can scratch sensitive surfaces.