Leather can be thought of as a non-woven mass of fibrous collagen protein that is derived from animal skin and has been rendered biorefractive. The skin of an animal becomes biorefractive and is therefore made into leather through the tanning process. The tanning process permanently incorporates what amounts to a biocide into the collagen protein. Other desirable characteristics are imparted to the leather by oiling, coloring, finishing, waterproofing, shaping, and working.

Greasing is the process of incorporating fats, fats, and oils into the body of the leather. The presence of fats, fats and oils in leather lubricates the fibers and tends to waterproof the leather. Without sufficient internal lubrication, the fibers will wear and break due to friction, and the leather can crack.

Leather is given a color by dyeing or pigmentation. Depending on the media used, the coloration can be incorporated into the entire thickness of the leather, or it can be concentrated on and near the surface.

The finishing is a surface finish that is given to the material. The surface finish is a continuous organic matrix other than protein fibers. That organic matrix can vary from a latex paint to a wax. Clothing always refers to what is the outermost layer of organic matter of the leather. Thus, it is possible to “dress” a bandage, as it is possible to apply a wax polish to a painted leather surface. Before wax polishing, the organic matrix that is the outer paint layer of leather was the “dressing”.

Working the leather refers to the repeated bending of the leather to reduce stiffness. This is an entirely mechanical process.

HOW TO THINK ABOUT CHEMICALS FOR LEATHER CARE

All chemical leather treatments fall into one or more of these categories: fatliquoring substitutes, surface coatings, waterproofing and cleaners.

HOW CLEANERS WORK

Cleaners are chemicals or chemical preparations that are intended to remove foreign matter from leather. The trick with cleaners is that they have to be able to remove foreign matter without permanently changing the appearance of the leather being cleaned. Invariably the material to be removed from the leather is a solid or semi-solid, and the cleaning chemical is almost invariably a liquid. Cleaning is accomplished either by dissolving the solid matter or by lifting the matter from contact with the leather through a preferential wetting process. Preferential wetting means that the leather prefers to be in contact with the cleaning fluid rather than the solid contaminant.

In either case a solid dissolves or a contaminant is lifted, a cloth or sponge is almost always necessary to complete removal of the foreign matter from the leather. Foreign contaminating matter is transferred from the leather to the cleaning cloth.

The cleaning preparation must also be removed from the leather to fully restore the leather to its previous state of cleanliness. Cleaner that is not removed can become a foreign contaminant. Cleaner is removed by rinsing, transfer to a cloth or sponge, evaporation, or a combination of all three.

Rinsing is the process in which excess water is used to dissolve the leather cleaner and remove it. In effect, the rinse water replaces the cleaning chemical in the leather. The water, loosely bound to the mass of fibers, evaporates by itself. This cleaner removal process is effective as long as the leather itself is not adversely affected by getting wet.

If the leather to be cleaned is brushed, ie has a continuous matrix of organic matter on top of the fibers, then other brushing agents can be used to clean the leather product. Indeed, it is the superficial dressing that must be cleaned, not the deep mass of protein fibers. Water and other leather finishing agents are useful in removing contaminants from coated leather. Here also the processes of dissolution and preferential wetting occur, as well as the transfer of solid contaminants from one body to another. Therefore, cleaning, waxing and polishing can occur as part of a single process.

SILCONES AND LEATHER

Silicone is a type of synthetic oil, and the term silicone refers to a homologous series of organic chemicals that are based on a backbone of alternating silicon and oxygen. Organic side chains, most often methyl groups, are attached to the silicon atoms. The chains are terminated with methyl groups, making them unreactive. The chains can also be terminated with hydroxyl groups or with hydrogen, making them reactive.

Silicone oil is a lubricant, and when it is able to penetrate the mass of fibers it acts as a substitute fatliquor. The silicone imparts water repellency as well as shine and a nice “hand” or feel to the leather. Because silicone wets leather fibers so well, a moderate amount of silicone can be substituted for fatliquor without affecting the “breathability” of the leather. “Breathing” means that water vapor can pass through the mass of fibers. Leather can also be “stuffed” with grease or wax that blocks the passage of water vapor through the mass of fibers. The use of silicone allows the leather to become water repellent to a certain degree without the loss of this “breathing” quality. Filling the leather with grease makes it waterproof, but makes the leather unable to “breathe”.

Silicone is often an important component of leather polishes, especially those that require buffing to bring out the shine. The silicone helps smooth the wax crystals into a continuous shiny matrix and also contributes to gloss and water repellency.

Silicone is a very useful product in the care and cleaning of leather. It finds use as a fat liquor, in cleansers, and in dressings. The drawback of using silicone is that silicone has a very low surface tension and the function of other water based leather treatment chemicals may be affected because the silicone prevents the other product from wetting the leather.

HAND FOOT OIL

Ox foot oil is produced by extracting the feet and shins of cattle. It is usually yellow in color and has a low melting point. It is used to keep leather soft and supple, which means it acts as a lubricant for the protein fibers. As such, it acts as a substitute fat liquor.

DRESSINGS AND DYES

A dressing is a coating that is external to, and yet adheres to, the protein fiber mass. Typically, a dressing consists of a continuous organic matrix that may contain other types of materials, such as pigments. Because the coating is external, it is possible to overlay a dressing, such as when a leather object is polished with wax or waterproofed with a silicone-containing product. Dressings are used to provide a decorative and often protective layer over the fibrous mass, and much leather sold commercially is conditioned during the manufacturing process. A topping for a dressing is sometimes referred to as a top dressing.

Aftermarket leather dressings are intended to restore or enhance the dressing that was applied to the leather in the manufacturing process. Waxes, for example, often contain a matrix that matches the color of the coated leather, and the act of buffing leather with colored wax applies a coating that is a colorant, waterproofing agent, and adds a nice shine to the leather.

Dyes are dyes and pigments that give leather its color and are different from dressings. The dyes may be a component of a dressing product. Some leathers, during the manufacturing stage, are treated with coloring solutions that carry the coloring agents deep into the mass of fibers so that the leather retains its color even when scratched. Dyes are added to aftermarket dressings to make leather that has lost some of its color due to wear and weather look refreshed.

WATERPROOFING

Many aftermarket chemical preparations are made to make leather waterproof or water repellent. There is a slight difference in meaning between the two terms. Being waterproof means that water simply won’t get through the leather. The condition is achieved by filling the leather with wax and/or grease. Leather in this state often gets hot because it can’t breathe. It is waterproof because the spaces between the fibers have been largely filled with a waterproofing agent and water vapor is trapped close to the body. But in a torrential storm, waterproofing can be an essential property of leather.

Being water repellent means that water does not soak into the leather, but because leather remains permeable, liquid water can be forced through the leather by pressure. Water repellent leather can breathe because water vapor can escape through the fibers even if liquid water cannot wet them. The water repellency of leather is usually achieved by a silicone treatment. The silicone remains liquid and wets the fibers, forming a film on them that water cannot wet. The film is thin enough that the spaces between the fibers remain empty.

Of the two terms, waterproof is closer to the absolute than water repellent.

A degree of waterproofing or water repellency can be obtained through products that apply a surface finish to leather. It is the surface finish that provides resistance to liquid water penetration, not the mass of fibers.

COMMERCIAL PRODUCTS

The four functions of leather care are: cleaning, re-greasing, surface treatment and waterproofing. Aftermarket commercial leather care products offer one, some or all of these functions.

Waxes, greases, fats, and fatty oils naturally repel water; and most of them are useful lubricants for leather fibers. Therefore, mink oil and “dubbin” products act as waterproofing agents as well as substitute fatliquors, each being better at one function than the other.