Manufacturing of Rosin

Rosin is the resinous component of the oleo-resin exuded by various pine species, commercially known as crude turpentine. The process of separating oleo-resin into essential oil (spirit of turpentine) and common rosin involves distillation in large copper stills. The essential oil is extracted at temperatures between 100° and 160°C, leaving behind fluid rosin, which is then tapped from the bottom of the still and purified by passing it through straining wadding.

Rosin Colors and Grades

The color of rosin can vary greatly, influenced by both the age of the tree from which the turpentine is sourced and the level of heat used in distillation. This can result in rosin that ranges from an opaque, almost pitch-black substance, through shades of brown and yellow, to an almost perfectly transparent, colorless, glassy mass. There are many commercial grades of rosin, categorized by letters. The darkest grade is A, progressing through to N, which is extra pale. Above these are the superior grades W, known as window glass, and WW, referred to as water white, the latter being about three times more valuable than the common varieties.

Rosin Sources

The main regions for rosin production include Indonesia, southern China (such as Guangdong, Guangxi, Fujian, Yunnan, and Jiangxi), and northern Vietnam.

In the United States, the South Atlantic and Eastern Gulf states are key areas for rosin production, primarily from Longleaf Pine (Pinus palustris) and Loblolly Pine (P. taeda). In Mexico, most rosin comes from live tapping (gum rosin) of various pine species, especially Pinus oocarpa, Pinus leiophylla, Pinus michoacana, and Pinus montezumae, with production concentrated in the west-central state of Michoacán.

Europe’s main source of rosin is the French district of Les Landes in Gironde and Landes, where Maritime Pine (P. pinaster) is extensively cultivated. In northern Europe, rosin is obtained from Scots Pine (P. sylvestris), and throughout Europe, local supplies come from other pine species, with Aleppo Pine (P. halepensis) being particularly important in the Mediterranean region.

Alternative Sources

Rosin can also be sourced from the distillation of Crude Tall Oil (CTO), a by-product of the kraft paper-making process, known as tall oil rosin. Another source is aged pine stumps, producing what is typically called wood rosin. In this method, the stumps are chipped and soaked in a solvent solution, with the solvents, rosin, fatty acids, turpentine, and other constituents recovered through distillation.

On a larger scale, rosin undergoes destructive distillation to produce rosin spirit, pinoline, and rosin oil. Rosin oil is used in the formulation of some solid lubricating greases and serves as an adulterant in other oils.

Rosin Hazards

Extended exposure to rosin fumes during soldering can lead to occupational asthma, historically referred to as colophony disease in this context, in susceptible individuals. The specific component of the fumes responsible for this issue remains unknown.