Colophony

Rosin (), also known as colophony or Greek pitch (), is a resinous material obtained from pine trees and other plants, mostly conifers. The primary components of rosin are diterpenoids, i.e., C₂₀ carboxylic acids. Rosin consists mainly of resin acids, especially abietic acid. Rosin often appears as a semi-transparent, brittle substance that ranges in color from yellow to black and melts at stove-top temperatures.

In addition to industrial applications such as in varnishes, adhesives, and sealing wax, rosin is used with string instruments on the bow hair to enhance its ability to grip and sound the strings, and it provides grip in various sports and activities. Rosin also serves as an ingredient in medicinal and pharmaceutical formulations and can cause contact dermatitis or occupational asthma in sensitive individuals. It is an FDA approved food additive.

The name "colophony" originates from , Latin for "resin from Colophon" (), an ancient Ionic city.

Properties

Rosin is brittle and friable, with a faint pine odor. It is typically a glassy solid, though some rosins will crystallize, especially when brought into solution. The practical melting point is variable, some being semi-fluid at the temperature of boiling water, others melting at . It is flammable, burning with a smoky flame. It is soluble in alcohol, ether, benzene and chloroform.

Rosin, consisting mainly of abietic acid, combines with caustic alkalis to form salts (rosinates or pinates) that are known as rosin soaps. They are used in soap making.

Uses

* It is rubbed on the hair of bows for bowed string instruments to increase friction.

* It has been used for centuries for caulking ships.

* It is approved by the US FDA as a miscellaneous food additive.

* It is an ingredient in printing inks, photocopying and laser printing paper, varnishes, adhesives (glues), soap, paper sizing, soda, soldering fluxes, and sealing wax.

* It 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 a flux used in soldering. The lead-tin solder commonly used in electronics has 1 to 2% rosin by weight 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 is frequently seen as a burnt or clear residue around new soldering.

* Rosin is also sometimes used as internal reinforcement for very thin skinned metal objects - like silver, copper or tin plate candlesticks, or sculptures, where it is simply melted, poured into a hollow thin-skinned object, and left to harden.

* 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 ("mastic"), 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 fingertips.

Rosin is extensively used for its friction-increasing capacity in several fields:
* Ballet, flamenco, and Irish dancers are known to rub the tips and heels of their shoes in powdered rosin to reduce slippage on clean wooden dance floors or competition/performance stages. It was at one time used in the same way in fencing and is still used as such by boxers.
* Gymnasts and team handball players use it to improve grip. Rock climbers have used it in some locations.
* Olympic weightlifters rub the soles of their weightlifting boots in rosin to improve traction on the platform.
* It is applied to the track surface at the starting line of drag racing courses to improve traction.
* Bull riders rub rosin on their rope and glove for additional grip.
* Baseball pitchers and ten-pin bowlers may use a small cloth bag of powdered rosin for better ball control. Baseball players sometimes combine rosin with sunscreen, creating a very sticky substance that allows far more grip on the ball than the rosin alone will; the use of such a substance is a violation of Major League Baseball rules.
* Rosin can be applied to the hands in aerial acrobatics such as aerial silks and pole dancing to increase grip.

Other uses that are not based on friction:
* Fine art uses rosin for tempera emulsions and as painting-medium component for oil paintings. It is soluble in oil of turpentine and turpentine substitute, and needs to be warmed.
* In a printmaking technique, aquatint rosin is used on the etching plate in order to create surfaces in gray tones.
* In archery, when a new bowstring is being made or waxed for maintenance purposes, rosin may be present in the wax mixture. This provides an amount of tackiness to the string to hold its constituent strands together and reduce wear and fraying.
* Dog groomers use powdered rosin to aid in removal of excess hair from deep in the ear canal by giving the groomer a better grip to grasp the hairs with.
* Some brands of fly paper use a solution of rosin and rubber as the adhesive.
* Rosin is sometimes used as an ingredient in dubbing wax used in fly tying.
* Rosin is used hot to de-encapsulate epoxy integrated circuits.
* Rosin can be mixed with beeswax and a small amount of linseed oil to affix reeds to reed blocks in accordions.
* Rosin potatoes can be cooked by dropping potatoes into boiling rosin and cooking until they float to the surface.

Rosin and its derivatives also exhibit wide-ranging pharmaceutical applications. Rosin derivatives show excellent film forming and coating properties. They are also used for tablet film and enteric coating purpose. Rosins have also been used to formulate microcapsules and nanoparticles.

Glycerol, sorbitol, and mannitol esters of rosin are used as chewing gum bases for medicinal applications. The degradation and biocompatibility of rosin and rosin-based biomaterials has been examined in vitro and ex vivo.

Rosin soaps and esters

Treatment of rosin with sodium hydroxide or sodium carbonate converts the abietic acid into its sodium salt, which is known as a soap. Whereas most domestic soaps are sodium salts of straight-chain fatty acids, the rosin soaps have the branched and cyclic backbone associated with abietic acid. Rosin soaps, also called rosinates, are used to "size" paper, a process that gives paper a desirable hydrophobic texture.

The conversion of abietic acid to esters is also practiced commercially. Ester of glycerol and methanol are both of interest. These materials are colorless syrups. They are compounded with polymers as tackifiers.

Violin rosin

Players of bowed string instruments rub cakes or blocks of rosin on their bow hair so it can grip the strings and make them "speak", or vibrate clearly. Occasionally, substances such as beeswax, gold, silver, tin, or meteoric iron are added to the rosin to modify its stiction/friction properties and the tone that can be produced. Powdered rosin can be applied to new hair, for example with a felt pad or cloth, to reduce the time taken in getting sufficient rosin onto the hair. Rosin is often reapplied immediately before playing the instrument. Lighter rosin is generally preferred for violins and violas, and in high-humidity climates, while darker rosins are preferred for cellos, and for players in cool, dry areas. There are also specific, distinguishing types for basses.
* Violin rosin can be applied to the bridges in other musical instruments, such as the banjo and banjolele, in order to prevent the bridge from moving during vigorous playing.

The type of rosin used with bowed string 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