Mineral Oil

There is some question as to whether or not mineral oil should be used on shoe/boot leather. I can tell you that you should avoid using mineral oil on your shoe and boot leather if you can.

The reason I say “if you can” is because a number of leather conditioners and leather protectors include mineral oil. Fortunately they will typically state something along the lines of “Contains petroleum by-products” or “Contains petroleum distillates” somewhere on the label. Some tanneries also use mineral oil in their fatliquoring process.
neatsfoot oil

Mineral oil is a basic straight chain hydrocarbon and comes is various grades defined by the carbon atom count, which ranges from 18 to 30 carbon atoms. Mineral oil used in shoe products has a molecular composition of about C25H52 (25 Carbon, 52 Hydrogen). Mineral oil is also a non-polar hydrocarbon and as such cannot have a pH value.
mineral oil 1

Mineral oil is also extremely hydrophobic because it is a non-polar substance, and the molecular structure has fewer reactive tertiary hydrogen and carbon atoms which minimizes direct reaction with oxygen. What this means is that mineral oil is much more of a water barrier than triglyceride based oils like animal and vegetable fats. In fact mineral oil is considered to be occlusive (a stop to moisture), whereas triglyceride based oils are considered semi-occlusive (allowing your shoes to pass perspiration for evaporation to some degree). Moisture, trapped in the leather by mineral oil, can lead to dry rot of the leather over time.

Another aspect of mineral oil is how it oxidizes: All oils oxidize over time, even mineral oil. Oxidation at the molecular level can happen in one of two ways: the gain of oxygen atoms, or the loss of hydrogen atoms. Because triglycerides already involve oxygen bonding in their molecular makeup they oxidize through increased oxygen. Since mineral oil can’t really bond with oxygen (for the same reasons it is hydrophobic) it must oxidize through the loss of hydrogen (as a side note: hydrocarbon molecules can be oxidized with oxygen atoms, but only at very high temperatures).

This loss of hydrogen atoms begins breaking down the molecular composition of the mineral oil (originally C25H52) and as it breaks down it becomes more volatile (the molecular composition of naphtha [the petroleum by-product used as a solvent in shoe polish –and other things] can be as big as C12H26). The smaller the size of a hydrocarbon molecule the more volatile (and toxic) it becomes. This is the reason mineral oil is never used to maintain old leather in museums and such.

So why is mineral oil used in shoe/boot care products and in fatliquoring? Mineral oil is used because it is very cheap compared to triglyceride based oils, and it provides a stronger moisture barrier.

Unfortunately, if you plan to keep your shoes/boots longer than a few years, the mineral oil will do more harm than good.

3 thoughts on “Mineral Oil

  1. Hi, I have a question that you might be able to help me with. I have a pair of synthetic leather boots (“all man-made material”), and I wonder if I should use mineral oil to polish it as oppose to regular shoe polish (which I have used before and it does not work). Would mineral oil damage vegetarian leather? Please let me know what you think, and thank you for your time!

    • Synthetic leather is typically composed mostly of polypropylene and/or polyurethane, and does not have protein fibers like leather (which require oil to keep the leather supple). Synthetic leather can dry out from UV exposure (sunlight) and dirt over time, and should be protected.

      It is a fairly common practice to use mineral oil on synthetic leather; because it is not absorbed into the material so much as it creates a surface barrier. However, mineral oil can also magnify the UV radiation (like putting baby oil on your skin and lying out in the sun), which is detrimental to the synthetic leather.

      I would probably suggest using Venetian Shoe Cream if you want to shine your synthetic leather boots. Venetian Shoe Cream contains turpentine (which helps in cleaning the surface) and petroleum distillates in the paraffin range (similar to mineral oil, but denser).

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