Rosin

Rosin, formerly called colophony or Greek pitch (Pix græca), is a solid form of resin obtained from pines and some other plants, mostly conifers, produced by heating fresh liquid resin to vaporize the volatile liquid terpene components. It is semi-transparent and varies in color from yellow to black. At room temperature rosin is brittle, but it melts at stove-top temperatures. It chiefly consists of different resin acids, especially abietic acid.

Rosin is also known as colophony or colophonia resina from its origin in Colophon, an ancient Ionic city.

Uses
Rosin is an ingredient in printing inks, varnishes, adhesives (glues), soap, paper sizing, soda, soldering fluxes, and sealing wax.

Rosin can be used as a glazing agent in medicines and chewing gum. It is denoted by E number E915. A related glycerol ester (E445) can be used as an emulsifier in soft drinks. In pharmaceuticals, rosin forms an ingredient in several plasters and ointments.

In industry, rosin is the precursor to the flux used in soldering. The lead-tin solder commonly used in electronics has about 1% rosin as a flux core helping the molten metal flow and making a better connection by reducing the refractory solid oxide layer formed at the surface back to metal. It's frequently seen as the burnt or clear residue around new soldering.

A mixture of pitch and rosin is used to make a surface against which glass is polished when making optical components such as lenses.

Rosin is added in small quantities to traditional linseed oil/sand gap fillers, used in building work.

When mixed with waxes and oils, rosin is the main ingredient of mystic smoke, a gum which, when rubbed and suddenly stretched, appears to produce puffs of smoke from the finger tips.

Rosin is extensively used for its friction-increasing capacity:


 * Bowed string players rub cakes or blocks of rosin on their bow hair so it can grip the strings and make them speak. Extra substances such as beeswax, gold, silver, tin, or meteoric iron are sometimes added to the rosin to modify its stiction/friction properties, and (disputably) the tone it produces. Powdered rosin is often applied to new hair, for example with a felt pad or cloth, to reduce the time taken in getting sufficient rosin onto the hair.


 * Violin rosin can be applied to bridges in other musical instruments, such as the Banjo and Banjolele, in order to stop the bridge moving during vigorous playing.


 * Ballet dancers sometimes rub their shoes in powdered rosin to reduce slipping before going on stage - it was at one time used in the same way in fencing.


 * Bull riders rub rosin on their rope and glove for additional grip.


 * Baseball pitchers and ten-pin bowlers may have a small bag of powdered rosin nearby, to use on their throwing hand, for better control of the ball.

Production
Rosin 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 which the turpentine is drawn and the degree of heat applied in distillation, from an opaque, almost pitch-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.

Other sources of rosin includes rosin (called tall oil rosin) obtained from the distillation of Crude Tall Oil (CTO). Crude Tall Oil is a byproduct obtained from the kraft paper making process. Additionally rosin may be obtained from aged pine stumps. This type of rosin is typically called wood rosin. In this process, aged wood stumps are chipped and soaked in a solvent solution. The solvents are recovered along with the rosin, fatty acids, turpentine, and other constituents through distillation.

On a large scale, rosin 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.

Properties
Rosin is brittle and friable, with a faint piny odor. It is typically a glassy solid, though some rosins will form crystals, especially when brought into solution. The practical melting point varies with different specimens, some being semi-fluid at the temperature of boiling water, others melting at 100°C to 120°C. It is very flammable, burning with a smoky flame, so care should be taken when melting it. 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 varnishes (including fine violin 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.

Prolonged exposure to rosin fumes released during soldering can cause occupational asthma (formerly called colophony disease in this context) in sensitive individuals, although it is not known which component of the fumes causes the problem.

The type of rosin used for instruments is determined by the diameter of the strings. Generally this means that the larger the instrument is, the softer the rosin should be. For instance, double bass rosin is generally soft enough to be pliable with slow movements. A cake of bass rosin left in a single position for several months will show evidence of flow, especially in warmer weather.

Also see

 * Resin