Rosin is a solid form of resin obtained from pines and some other plants, mostly conifers, produced by heating fresh liquid resin to vapourise the volatile liquid terpene components. It is semi-transparent and varies in color from yellow to black. At room temperature it is brittle, but it melts at stove-top temperatures. It chiefly consists of different resin acids , especially abietic acid.
In industry it is the precursor to the flux used in soldering. The tin-lead solder commonly used in electronics has about 1% rosin as a flux core helping the molten metal flow and making a better connection. Rosin is an ingredient in printing inks, varnishes, glues, medicines, chewing gum, soap, paper sizing, and, in the olden days, sealing wax.
It is also extensively used for its friction-increasing capacity. Such uses include rosining the bows of stringed instruments such as violins or cellos to enhance sound production. For this purpose, extra substances such as gold and silver are added to the rosin for extra friction (and partly for sheer extravagance, as this can make the most expensive cakes cost hundreds of dollars.) Gymnasts, weight lifters, and baseball pitchers use a bag of powdered rosin to keep their hands dry and to increase their grip. Ballet slippers are also rubbed in powdered rosin to reduce slipping.
A mixture of pitch and rosin is used to make a surface against which glass is polished when making optical instruments such as lenses.
Rosin is also known as colophony or colophonia resina from its origin in Colophon, an ancient Ionic city. It is the resinous constituent of the oleo-resin exuded by various species of pine, known in commerce as crude turpentine. The separation of the oleo-resin into the essential oil-spirit of turpentine and common rosin is effected by distillation in large copper stills. The essential oil is carried off at a temperature of between 100° and 160° C, leaving fluid rosin, which is run off through a tap at the bottom of the still, and purified by passing through straining wadding. Rosin varies in color, according to the age of the tree from whence the turpentine is drawn and the amount of heat applied in distillation, from an opaque almost pitchy black substance through grades of brown and yellow to an almost perfectly transparent colorless glassy mass. The commercial grades are numerous, ranging by letters from A, the darkest, to N, extra pale, superior to which are W, window glass, and WW, water white varieties, the latter having about three times the value of the common qualities.
Rosin is a brittle and friable resin, with a faint piny odor; the melting-point varies with different specimens, some being semi-fluid at the temperature of boiling water, while others melt at 100° to 120° C. It is very flammable, burning with a smoky flame, so care should be taken when melting it. When melted to a thick fluid, it can be surprisingly ductile. It is soluble in alcohol, ether, benzene and chloroform. Rosin consists mainly of abietic acid, and combines with caustic alkalis to form salts (rosinates or pinates) that are known as rosin soaps. In addition to its extensive use in soap-making, rosin is largely employed in making inferior varnishes, sealing-wax and various adhesives. It is also used for preparing shoemakers' wax, as a flux for soldering metals, for pitching lager beer casks, for rosining the bows of musical instruments and numerous minor purposes.
In pharmaceuticals it forms an ingredient in several plasters and ointments. On a large scale it is treated by destructive distillation for the production of rosin spirit, pinoline and rosin oil. The last enters into the composition of some of the solid lubricating greases, and is also used as an adulterant of other oils.
The chief region of rosin production is the South Atlantic and Eastern Gulf states of the United States. American rosin is obtained from the turpentine of Longleaf Pine Pinus palustris and Loblolly Pine P. taeda. The main source of supply in Europe is the French district of Les Landes in the departments of Gironde and Landes, where the Maritime Pine P. pinaster is extensively cultivated. In the north of Europe rosin is obtained from the Scots Pine P. sylvestris, and throughout European countries local supplies are obtained from other species of pine, with Aleppo Pine P. halepensis being particularly important in the Mediterranean region.