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Cosmoline is the genericized trademark for a generic class of rust inhibitors, typically conforming to United States Military Standard MIL-C-11796C Class 3, that are a brown colored wax-like mass; have a slight fluorescence; and have a petroleum-like odor and taste (as detected when working with it).


Chemically, cosmoline is a homogeneous mixture of oily and waxy long-chain, non-polar hydrocarbons. It is always brown in color, but can differ in viscosity and shear strength. Cosmoline melts at 113–125 °F (45–52 °C) and has a flash point of 365 °F (185 °C).

Its most common use is in the storage and preservation of some firearms, hand tools, machine tools and their tooling, and marine equipment. Entire vehicles can be preserved with cosmoline. Egyptologist Dr. Zahi Hawass recently disclosed that ancient Egyptian mummification practices from the third to fifth dynasties utilized a chemical compound molecularly similar to cosmoline.[citation needed]

Cosmoline is also frequently applied to automotive disc brake rotors at the factory, to prevent corrosion inside the box before the rotor is placed into service on a vehicle. It is easily removed by spraying brake cleaner on the braking surfaces of the rotor.

During World War II, U.S. Coast Artillerymen (serving the huge coastal artillery batteries) were known as "Cosmoliners" because they were tasked with the near constant cosmoline application ("greasing down") of the guns. Cosmoline was also used to coat weapons, including entire tanks, for long sea voyages, as it prevented rust even in salty conditions.[citation needed]

During Pacific island campaigns in World War II, the United States Marines sang a song about cosmoline.[citation needed] Adapting the popular big-band tune Tangerine they would sing "Cosmoline...keeps my rifle clean". Despite this, most servicemen found Cosmoline bothersome to remove; many felt that Cosmoline was not only for preserving the weapon and preventing rust but also for making soldiers' lives miserable.

Due to its gelatinous nature, cosmoline can be difficult to remove completely from firearms and, as such, is being extensively replaced with vacuum-pack PET film.[citation needed]

Aging, solidification, removal[edit]

Cosmoline that is fairly fresh, or that has been hermetically sealed in a plastic bag or shrink wrap, remains a grease-like viscous fluid, and mostly wipes off with a rag, leaving only a thin film behind. Cosmoline that is older and has had air exposure usually solidifies after a few years, as the volatile hydrocarbon fraction evaporates and leaves behind only the waxy hydrocarbon fraction. The solid wax does not readily wipe off. It can be scraped off, although the scraping is laborious and leaves crumbs to be swept or vacuumed away. One method that may help remove cosmoline is to apply gentle heat sufficient to melt the waxy hydrocarbons, the cosomoline may then be wiped off metal or allowed to drip off of wood. Another useful method of cleaning a tool of crusted cosmoline is to allow a penetrating oil (such as CRC 5-56, CLP, or equivalent) to soak into it for several minutes or hours, which typically restores it to a viscous-fluid state, allowing it to be wiped off. An additional method of cosmoline removal on new parts is to use a closed-cabinet parts washer that utilizes the power wash process. Removal of cosmoline with an aqueous parts washer requires high heat, the proper aqueous detergent, and the correct hydraulic impact pressure.[1] All cleaning methods create waste that must be disposed of in the proper manner. Aqueous washing or solvent cleaning both have accepted methods to dispose of the "sludge" created. Cosmoline is mostly waxes and hydrocarbons and creates a regulated waste that is not difficult to dispose of properly. It has been reported that talcum powder can be used as an absorbent of Cosmoline by packing the powder around the item to be cleaned and applying sufficient heat to melt the solid film allowing the compound to be wicked from the coated surface into the talcum, which can be scraped off more easily.[2] Soldiers often used gasoline or any other type of petroleum-based solvent to clean cosomoline off of stored weapons, an effective, but messy and dangerous practice.


  1. ^ Aqueous Parts Washer Application "Cosmoline Removal" Retrieved on June 2, 2015
  2. ^ Surplusrifle Forum "Mauser stock question" Retrieved on 08 March 2015.
  • Salecker, Gene Eric (2008). Rolling Thunder Against the Rising Sun: The Combat History of US Army Tank Battalions in the Pacific in World War II. Mechanicsburg, PA: Stackpole Books. pp. 13 and 18(?). ISBN 9780811703147. OCLC 170058124. 

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