Neatsfoot oil

Neatsfoot oil is a yellow oil rendered and purified from the shin bones and feet (but not the hooves) of cattle. "Neat" in the oil's name comes from an old English word for cattle. Neatsfoot oil is used as a conditioning, softening and preservative agent for leather. In the 18th century, it was also used medicinally as a topical application for dry scaly skin conditions.

"Prime neatsfoot oil" or "neatsfoot oil compound" are terms used for a blend of pure neatsfoot oil and non-animal oils, generally mineral or other petroleum-based oils.

Fat from warm-blooded animals normally has a high melting point, becoming hard when cool – but neatsfoot oil remains liquid at room temperature. This is because the relatively slender legs and feet of animals such as cattle are adapted to tolerate and maintain much lower temperatures than those of the body core, using countercurrent heat exchange in the legs between warm arterial and cooler venous blood – other body fat would become stiff at these temperatures. This characteristic of neatsfoot oil allows it to soak easily into leather.

Modern neatsfoot oil is still made from cattle-based products, and is sometimes criticized for a tendency to speed oxidation of leather. This formulation does darken leather, which means that use on light-colored leather is likely to change its color. If mineral oil or other petroleum-based material is added, the product may be called "neatsfoot oil compound". Some brands have also been shown to be adulterated with rapeseed oil, soya oil, and other oils. The addition of mineral oils may lead to more rapid decay of non-synthetic stitching or speed breakdown of the leather itself.

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Wikipedia