What kind of oil should you use to treat and maintain wooden traditional weapons? I want an oil that can just be wiped onto the weapon and absorbed into the wood. I think we want an oil that won’t evaporate and let the wood dry out, won’t chemically react after application, and won’t leave a waxy deposit.
But as the title says, “Oils ain’t oils.” The major class of oils extracted from plants are mixtures of fats called triglycerides. These are chemically very different from mineral oils, which are petroleum derivatives. These are also often mixtures or different distillation fractions.
Camellia oil is recommended for treating traditional weapons. It is a widely used cooking oil in China instead of olive oil or sunflower oil. It has the highest content of mono-unsaturated fats that I can find. Olive oil is quite similar in composition, as are avocado and canola oil, so should be good substitutes. Sunflower oil comes in lots of different types.
Other plant-derived oils such as linseed and tung oil are known as drying oils, which contain more polyunsaturated fats. Some folks have mentioned treating weapons by soaking them in linseed oil diluted with kerosene. Kerosene is a light mineral oil that will evaporate and leave the drying oil behind.
Mel pointed out that linseed oil is also used for cooking but has a reputation for going rancid if left too long, and can be coloured: Chemically there are two main things I know of that relate to this. The first is oxidation: All unsaturated oils oxidise in air, but polyunsaturated oils react faster and tend to produce more highly coloured products. This process is accelerated by light. The second is polymerisation, by which individual oil molecules link together into a chain or network. Polyunsaturated oils are pretty good at this and that’s why they are used to make a tough coating or natural varnish.
Coconut oil and hydrogenated vegetable oils are saturated fats; these are more likely to crystallise and create a waxy feel.
Neatsfoot oil is made from rendering animals’ feet and used for leather treatment. It contains a mixture of mostly monounsaturated and some saturated and polyunsaturated fats so is probably also ok. However, it is often sold as a mixture with mineral oils as solvents. These will evaporate and may smell oily.
More aromatic and ‘essential’ oils like tea-tree, orange, lemon and eucalyptus are terpenes. These are chemically very different from triglycerides. They are mostly mixtures of small and volatile (faster evaporating) molecules that combine to give characteristic smells. Pinene is one common component of such oils; its name kind of tells you how it smells.
I think that’s why camellia oil is the “sweet spot” for maintaining traditional weapons. It has very low polyunsaturated and saturated fat content but is high in monounsaturated components. Olive oil is a close second.