Section II
Agents for Cleaning and Preserving Leather
4. GENERAL-There are so many agents used for cleaning and preserving leather, both raw chemicals and mixtures of them sold under trade names, that it would be impracticable to list all of them here. In an effort to give some idea, however, of the composition and properties of a few of the better known and more generally used ones, the tabulation indicated in succeeding paragraphs has been made.
5. CLEANING AGENTS.-Cleaning agents are as follows:
a. Soap -The purpose of all soaps is to clean, which they do by exhibiting, in their lathered state, an attraction for the dirt particles exceeding the attraction of the leather for them. Formed generally by the union of a fatty acid with a base (compound of a fat with an alkali), soaps should not be caustic if they are to be used on leather; they should also, to be classed as "saddle soaps", possess some fixed oils that assist in preserving the leather after the lather itself has cleaned it. If properly used, the saddle soaps will clean the leather and at the same time, at least to an extent, oil it. A proper method for day-to-day cleaning and preserving is to work up a light lather with saddle soap and sponge, going lightly over both the inside and outside surfaces of the leather and working the lather into it, after which any excess of the lather may be removed with either an almost dry sponge or with a light flannel cloth. It must be emphasized that in day-to-day cleaning and preserving with soap as little water as possible should be used in working up the lather, so that the lather itself will be "light and dry". If it is desired periodically, to thoroughly clean with soap, as prior to oiling, the lather should be heavy and wet, which will require the use, in contrast to daily care, of copious amounts of water. A proper method of thoroughly cleaning with soap will be outlined in a succeeding paragraph, "Preparing Leather for Storage". Satisfactory soaps are considered to be:
- Glycerin soap which is considered to be a superior cleaner and preservative, but relatively expensive. The imported item is usually better, although more expensive than the domestic, with the domestic constantly improving in quality.
- Castile soap, which is an excellent cleaner, and the oils of which are excellent preservatives for long periods if the leather is given only normal usage.
- Saddle soaps, which are made especially for the purpose of cleaning and preserving leather, many brands of which are satisfactory. Some imported saddle soaps are considered excellent but are expensive, many domestic saddle soaps being as satisfactory when the item of cost is considered. The saddle soaps to avoid are the cheap ones, which are apt to contain burnt fats, and which are likely to decompose into the soap's original components. If decomposition has begun (as is the case with some issue tins which have been in storage for long periods), leather cleaned with it will have a greasy feeling and will collect dust and dirt rapidly. The dust and dirt will not only be ground into the surface of the leather, causing it to deteriorate and discolor more rapidly than normal, but will also cause boots, breeches, and other items of equipment to become soiled quickly.
b. Chemicals.-The purpose of all chemical cleaning agents is to dissolve the undesirable fats or fatty acid compounds that might be present in leather, to chemically reduce organic matter, to loosen coloring matter, or to bleach. Great care must be taken in their selection to insure using no agent that will have a deleterious effect upon either the surface or body of the leather. Among such undesirable agents would be strong acids or caustic alkalis; while among the agents considered suitable, in proper solution, are the following:
(1) Ammonia water, which is a solution in water of ammonia (a gas composed of nitrogen and hydrogen). It is highly volatile, and has a very characteristic penetrating odor. It combines with acids to from ammonium compounds, and with fatty acids to form ammonium soap, the most soluble soap and one of the best leather cleaners known. It also assists in loosening corrosion and verdigris from metal, and from leather stained by metal fittings, after which it may be more easily removed by soap or mechanical means.
- Oxalic acid, which is a mild vegetable acid, formed generally by the decomposition of sugar by nitric acid. In proper solution, it is perhaps the best known and most generally used bleaching agent for leather, being used almost universally during the tanning process for the production of all so-called "blond" leather, and leather which, after bleaching, is to be dyed bright colors. The fact that it is a poison should be impressed on all using personnel, and its use supervised accordingly.
- Alcohol (Wood or Methyl), which is a colorless liquid obtained by a process of distilled organic matter. It is an excellent cleaning agent or solvent, especially for "wet" or "dry" dyes, and, in addition, acts well as a "carrier" for bleaching agents. The fact that it is a dangerous poison if taken internally should be impressed on all personnel using it.
- Acetic acid, which is a mild, colorless acid (C2H4O2) produced by the oxidation of common alcohol and many other organic substances. It is often useful in a weak solution for neutralizing the basic (alkaline) dye reactions in leather. Commercial vinegar is a dilute and impure acetic acid produced by acetic fermentation of dilute alcoholic liquids, such as cider or malt.
The above chemicals may be purchased for the following approximate prices:
Oxalic acid crystals…………………15½ cents per gallon
Wood alcohol……………………….40½ cents per gallon
26° Ammonia water…………………60 cents per gallon
Preserving Agents - The most common preserving agents are enumerated below:
a. Dubbins are compounds usually of a rendered, unsalted animal fat, such as beef or mutton tallow, mixed with other preservative substances. When properly applied to the previously cleaned leather, they are considered excellent preservative agents, either in preparing leather for storage or, in some cases, for leather in daily use. Compositions of the more generally used dubbins are as follows:
(1) 20 lbs. beef tallow, ½ lb. rosin, 5 gals. inedible cod-liver oil, ½ lb. melted bees wax
Excellent for preparing leather for storage.(2) 50% beef tallow, 50% glycerin. Excellent preservative for leather in use.
(3) 40% mutton tallow, 60% prime neat's-foot oil. Excellent preservative for leather in use.
(4) 50% beef tallow, 50% prime neat's-foot oil. Excellent preservative for leather in use.
(5) 50% mutton tallow, 50% neat's-foot oil, small amount melted bees wax. Excellent preservative for preparing leather for storage.
In the preparation of all dubbins, great care must be exercised in rendering the unsalted tallow to prevent the burning of the fats, which would make the resultant tallow, and therefore a dubbin made from it, unsuitable. In order to remove as many impurities as possible, the suet should be cut into small pieces and put into a suitable utensil, with sufficient water added to prevent burning, and rendered out slowly, all cracklings (pieces of flesh, etc.) being removed as they appear on the surface. After rendering, the melted tallow should be strained first through a coarse colander and finally through a very fine colander, then allowed to cool and solidify. After solidifying, the tallow should appear white and clean. The water which will be at the bottom of the container should be removed by piercing the layer of solidified tallow with an ice-pick or other implement, and turning the container upside down to allow it to drain off.
In order to prepare all dubbins, the ingredients are heated together until melted sufficiently to mix well, preferably in a double boiler, to avoid burning the fats. It is best after they are prepared to place all dubbins in small containers, such as olive or pickle jars, so that during the process of their use the contents can be shaken to insure their being properly mixed when applied.
Before applying the dubbin it should be melted by heating in a double boiler and then it should be allowed to cool until lukewarm (never above a temperature than can be borne by the hand) and applied to the leather with a small sponge, piece of sheepskin, or other suitable agent. The applicator should be saturated with the warm, thoroughly mixed dubbin, and the dubbin applied to the article, first spreading it quickly over the entire surface of the still slightly damp (previously cleaned) leather, then rubbed in well by band. Any excess that remains after a short time has been allowed for the dub-bin to penetrate the leather should be wiped off with a clean, dry cloth. The leather is then ready for storage, or if to be used currently, the oil should be allowed to penetrate for a period of about twenty-four hours, after which the excess surface oil should be removed by a cleaning with soap before the leather is dressed and put into service.
b. Glycerin is a clear, colorless liquid of thick syrupy consistency, made by the hydrolysis of animal fats or fixed oils, purified by distillation (as by action of super-heated steam on palm oil). It is slightly antiseptic, and is a solvent for fixed alkalies or alkaloids. It is an emollient, hygroscopic (absorbs moisture from the atmosphere), does not evaporate or become rancid, and is much used as an ingredient of lotions and ointments. Mixed in proper proportion with other substances, it is considered an excellent leather preservative and softener.
c. Oils suitable for preserving leather may be animal, vegetable, or mineral derivatives, but generally the animal oils are considered superior, with few exceptions, for this purpose. Among the more generally used oils are the following
(1) Neat's-foot oil, which has long been recognized as the best of all oils for leather. It is a pale yellow, fixed oil, made by boiling the feet, less hoofs, and skin bones of "neat" cattle (cattle of the ox type as distinguished from horses, sheep and goats). It is the preservative base of many saddle soaps and an ingredient of many oil polishes. Due to the fact that it is difficult and expensive to obtain in its purest or "prime" state, many commercial products termed "neat's-foot" are likely to have been "cut" with some mineral oil.
(2) Petroleum jelly, which is obtained from refining mineral crudes, applied very lightly to leather surfaces is believed by some to protect leather equipment from the harmful effects of sea air during overseas shipment. Useful for this purpose also would be any of the more generally used dubbins, to which a small amount of paraffin has been added.
(3) Castor oil, which is generally obtained from the castor bean, but may be derived chemically from other sources. Chemically, it is a combination of glycerin, fatty acids, and ricinoleic acid. The acids in castor oil are undesirable constituents of an oil to be used in preserving leather, but many officers have used castor oil with great success in dubbins, and in combination with saddle soaps. In these cases, the undesirable acid effects of the oil are apparently neutralized, at least to a large extent, by the combination of the acids with the fats in the dubbin or with the alkalis in the soap. If used with the soap, caution is recommended in the amount applied, for if too large an amount is applied, or if allowed to penetrate too long before soaped, the leather is likely to be so softened, as for example in the case of saddle skirts, that the "body" of the leather is lost, and its strength undesirably reduced. Like glycerin, however, if used properly, castor oil has the advantage that it will not appreciably darken the leather on which it is used.
(4) Other oils known to be good leather preserving agents, but which either are likely to excessively darken leather, to turn rancid, or to be too expensive, are olive oil, unsalted butter, and palm oil.
It must be realized that the application of any oil will darken, to an extent, any previously bleached leather, and that too much of any oil is deleterious to leather and will greatly lessen its tensile strength. In this last connection, it might be said that more leather equipment has been ruined, or its serviceability impaired, by the application of too much or too hot oil than ever by the application of an insufficient amount. In order to properly apply any oil, a piece of woolen cloth, such as a small square of salvaged blanket, should be dipped into the preferably warm but never hot oil, squeezed out, then passed lightly over the whole surface of the almost, but not quite dry, previously cleaned leather, and finally the surface oil rubbed in by hand. After oiling, the oil should be allowed to penetrate, and the leather "dry out", which may take twenty-four or more hours. Thereafter, especially while in storage, any excess oil appearing on the surface of the leather or exuding from its pores, should be removed with a clean, dry cloth. Before being "dressed", any excess oil remaining on the surface of the leather should be removed by cleaning with soap.
d. Dressings or polishes are used not only to assist in preserving the leather but to give it a luster. Any of the better grades, applied according to directions, should be satisfactory. If it is desired to make a polish, the following formula would probably prove satisfactory:
Melt together 55 parts of carnuba wax and 55 parts of crude montan wax (221° F.) ; add 10 parts nigrosine base (for black leather), or 10 parts other color dye-stuff soluble in oil (for other than black leather), dissolved in 20 parts stearic acid; then add 150 parts ceresine (a form of wax) and finally 900 parts oil of turpentine.
e. Waxes have for their object the imparting of a luster to the leather, as for inspection, etc. Any standard grade of wax, or wax polish, should prove suitable, provided no "wax cleaner", which might contain ingredients injurious to leather, is used. The wax should generally be applied with a very slightly dampened soft cotton cloth that has been impregnated with wax, the leather being given a very light coat. Then, before the wax is dry, it should be spread with a soft brush, and the final polishing given with a soft woolen cloth.