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=== Past practice ===
* In 19th-century machining practice, it was not uncommon to use plain water. This was simply a practical expedient to keep the cutter cool, regardless of whether it provided any lubrication at the cutting edge–chip interface. When one considers that [[High speed steel|high-speed steel]] (HSS) had not been developed yet, the need to cool the tool becomes all the more apparent. (HSS retains its hardness at high temperatures; other carbon tool steels do not.) An improvement was soda water ([[sodium bicarbonate]] in water), which better inhibited the rusting of machine slides. These options are generally not used today because more effective alternatives are available.
* Animal fats such as [[Tallow]] or [[Lard]] were very popular in the past.<ref>{{Harvnb|Hartness|1915}}, [https://archive.org/details/hartnessflattur00hartgoog/page/n160 <!-- quote=james hartness flat turret lathe manual. --> pp. 153–155].</ref>
* Old machine shop training texts speak of using [[Lead tetroxide|red lead]] and [[white lead]], often mixed into lard or lard oil. This practice is obsolete due to the toxicity of lead.
* From the mid-20th century to the 1990s, [[1,1,1-Trichloroethane|1,1,1-trichloroethane]] was used as an additive to make some cutting fluids more effective. In shop-floor slang it was referred to as "one-one-one". It has been phased out because of its [[Ozone depletion|ozone-depleting]] and [[central nervous system]]-depressing properties.
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