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This letter was sent to a collector by the United States Air Force Musuem. This was in response to a question on how they preserve their artifacts. This is a technical guidance paper that dealt with the preservation of leather objects in the museum's collection written by the staff conservator. A source guide for the products recommended is listed at the bottom of the page.

USAFMP, TECHNICAL GUIDANCE

THE PRESERVATION OF LEATHER OBJECTS

This paper deals with some of the aspects of protecting and preserving the leather objects in your collections. Leather objects make up a great deal of most collections and pose special problems and considerations to personnel tasked with their care and preservation

Leather or the tanned, dressed skin or hide of animals is one of the oldest materials used by mankind. It has been used since prehistoric times for such items as clothing, bags, shelter, tying, attaching, harnessing, footwear, and backing. It is an organic material and is susceptible to the deterioration that all such materials suffer. Leather can be made supple or stiff, porous or water repellent, decorative or plain. Whether derived from the skin/hides of cattle, oxen, buffalo, horse, pigs or sheep, it is still broadly referred to as 'leather'.

Basically speaking, leather is an animal skin consisting of protein matter that will putrify or deteriorate rather quickly if not treated. The immediate treatment is to salt the hide to stop putrification, but the most important long term treatment is called tanning. Taning makes leather resistant to putrification and pliable even when it is dry. There is a chemical change brought on by the 'tanning' which are used in the process. The tanning react with the proteins of the skin and thus produce the desired effects of stabilization and pliability. In military museums, most if not all of the 'service' leathers are vegetable tanned or vegetable/chrome tanned cowhide, horsehide of sheep skin. So, the treatments and procedures discussed will deal with these service leathers.

Service leathers are found in footwear, purses, jackets, instrument cases, hats, helmets, gloves, straps for various clothing accoutrements, and in various military vehicles such as jeeps, trucks, tanks and aircraft. There are various examples of sheepskin or 'shearling' leather as well as horsehide to be found in U.S. cold weather/high altitude uniforms (shearling), and in the U.S. A-2 jacket (Some A-2's were modified with or made entirely from horse hide). All of these examples and others are found in the USAF museum Program collection and all of them need special attention to preserve them for future musuem study and exhibition.

The care of a leather object begins as soon as it arrives in your collection and you should be aware of the various conditions in which it may arrive. Developing an eye for those conditions is assential in determining the action which should be taken to preserve the object. Is the leather dry to the touch? Is it cracking? Does reddish-brown powder or dust drop off of the object when it is handled? Is the leather soiled? Does it show signs of mold, mildew, fungus or insect infestation? Are there holes or tears or overstressed areas? Is there verdigris (waxy green deposit) around brass, bronze, or copper fixtures? Is there rust around steel fixtures? Has the leather been over-treated with heavy oils? Does the object have 'War Art' painting? What is the condition of the art? Only after answering these questions can further attention and proper care be given to the object.

Cleaning:

There was a time in the not so distant past that all leather objects in museums were routinely subjected to a saddle soaping for preservation. I have found that unnecessary washing of leather is unwarranted and may actually be detrimental to the leather. First, it removes along with dirt, some of the natural moisture of the leather. Secondly, it is much harder to remove excess saddle soap residue from the leather than may be supposed. I have seen U.S. A-2 jackets with a visible saddle soap residue not evident 10 years ago when they were initially treated. You must be well versed in the use of saddle soap and water as it is possible to use too much of either and the results are not always beneficial.

With this in mind, the general rule of thumb is that the use of saddle soap to clean leather should be limited to objects with light oily/dirt soiling (the type found in the collar area of a jacket). The cleaning should be judicious and limited to those soilied areas of the object and not the entire object! Do not use saddle soap on suede or 'rough out' leather. Suede must be cleaned with dry cleaning methods as should the heavily oil/soiled areas of leather. Dry cleaning should be attempted only by a trained conservator or professional dry cleaner who specializes in leather and furs.

The saddle soap should be of a top quality such as Propert's or Kiwi. Do not use the G.I. saddle soap; the quality is very inconsistent. Proper applications begins by brushing the leather with a soft brush to remove all surface dust, etc. Then, saddle soap is worked into a lather with a soft, damp sponge (not wet). The lather and only the lather should be applied to the object and rubbed in a circular motion with a nearly dry sponge. The sponge should be rinsed and squeezed out to remove all dirt and water before it is re-applied to the leather. This step is repeated 5-6 times to assure that all soap residue is removed. Directly applying saddle soap without water is detrimental to leather. It is very hard to remove residue effectively without using large amounts of water, that, in turn leads to damage. Apply the lather and work in in with a short swirling motion. The object should be left to air dry (not force dried) in its normal shape.

Preservation Treatment:

The most common forms of deterioration in leather are due to prolonged dryness, mold, mildew and fungus, U/V light, insects and vermin, and last but not least, the reaction of the 'tanning' with atmospheric pollutants such as sulphur dioxide (acid rain). Thus, leather needs to be protected from these agents of deterioration. Mold, mildew, fungus and chemical attach can be detetted through the application of a solution of 7% Potassium Lactate and 1/4% Paranitrophenol to the object. If the object shows signs of mold spores, it shold be brushed with a medium nylon bristle tooth brush to remove the spores before application of the protective solution. This solution is available in a liquid pre-mixed product marketed by Talas, Division of Technical Library Services, 213 W. 35th, New York, NY 10001. It is called Talas Leather Protector and comes in gallons. It is a deacidifier, cleaner, buffering salt and fungistat which will also prevent the occurance of 'red rot' which so often attacks vegetable tanned leather. It is basically non-toxic to humans, but rubber gloves should be worn when applying any solvents, liquids, etc. The protector should be applied sparingly but thoroughly, using a soft cloth or sponge. It should be allowed to soak into the leather and air dry. This product is very valuable in conserving your leather objects.

Any application of the protector or dressings to areas where there is 'War Art' involved should be done slowly using Q-tips to work the solution/dressing into leather around the art and light pressure so as to not disturb the painted surfaces.

'Feeding' the Leather:

Dry, rigid or brittle leather may be made flexible again by proper lubrication or replacement of natural moisture with emollients such as neat's foot oil, cedarwood oil, lanolin or a combination of these. The proper ratio of neat's foot oil to lanolin is 60% neat's foot oil to 40% lanolin. SInce lanolin generally is found in a semi-solid form, it has to be heated to reduce it to a liquid before mixing with the neat's foot oil. This is a purist, traditional method of making leather dressing which is unnecessary in today's applications. Talas markets a pre-mixed leather dressing combining these two oils. It is marketed as Talas Leather Dressing. My experience has shown me that the best all around leather dressing is British Museum Leather Dressing or BMLD. It was develped by the British Museum and consists of lanolin, beeswax, cedarwood oil and hexane. The lanolin and cedarwood oil lubricate the leather fibers while th beeswax acts as a sealer and imparts a nice sheen to the leather when buffed. In the past, there has been some argument as to the merits of beeswax as it can leave the object slightly tacky in warmer climates. If this is a problem there is a ceresin formula which is basically the same but substitutes ceresin for the beeswax to eliminate tackiness. I have found that if the BMLD is applied properly and the object stored in a proper environment, tackiness is not a problem.

The BMLD should be applied with a soft lint free cloth such as cheese cloth etc., and should be applied sparingly in two coats seperated by 2 days absorption time. After the second coat and absorption time (2 days), the object should be wiped with soft, lint free cloth to remove any excess dressing and then buffed. I find that the beeswax or ceresin seals the leather grain when it is buffed and is an added ounce of prevention. It should be noted that all leather dressings will darken leather to some degree. This is generally acceptable and does not effect the items exhibit worthiness. This darkening actually helps to hide darkened oily stains in the leather. Remember: Avoid applying anything directly over painted areas of the leather.

The applications of any dressing should occur after the application of the Talas leather protector.

There are other worthy dressings which may be substituted. Lexol which contains lanolin, neat's foot oil and a mold, mildew deterrent: Renaissance Leather Reviver (Conservation Materials, Ltd., Sparks, Nevade) which contains lanolin, 1,1,1, trichloroethane,and mystox (mold inhibitor).

Proper Storage and exhibition of Leather Objects:

As stated earlier, the single most important aspect of leather preservation is enviromental control. The ideal enviroment for most leather objects is a relative humidity between 45% and 60% and a constant temperature of between 55 and 68 degrees F. The important aspect of those figures is not whether you acheive 50% RH and 65 degree F temp exactly, but that the temp & RH stay constant ! 'Spiking' temperature/humidity changes are detrimental to leather and most other objects in your collection.

Radiant light and heat should be avoided. This will cause chemical and physical changes in leather. Dyed or painted leathers should be protected from ultraviolet radiation as diligently as you would protect prints, documents, paintings and textiles.

Good house keeping is essential in leather care. Dust settling on leather can be very abrasive but even worse, it brings moisture and pollutants into contact with the leather and accelerates the onset of chemical decay (red rot). Leather may be stored and covered with plastic bags so long as the bottom is left open to facilitate air exchange.

Leather jackets, coats, etc., should be stored flat. Hanging adds a great deal of stress to the garmet. If they must be hung it should be on a well padded hanger. Avoid the use of any wire coat hangers that are not padded! Shoes and leather hats should be stuffed with acid free tissue to retain shape.

Exhibition of leather objects should be in cases designed with U/V filtering plexiglass and ventilated to assure air exchange. Again, temperature, humidity and light control are very important to your leather objects and cases should be designed and located with this in mind.

To avoid stressing leather objects on display, always place them on undersized mannequins.

Remember, leather is an organic, fibrous sunstance like yourself. If you're not comfortable in the enviroment, chances are neither is our leather collection.

Robert B. Adair

USAFMP/DMC
Objects Conservator

LEATHER PRESERVATION PROCEDURES

I. Cleaning of Leather Artifacts:

1. Determine whether the object will be able to tolerate the procedure. Use only quality saddle soap. (A) is it brittle, powdery or torn ? If so, do not further stress by saddle soaping.
2. Identify those areas which need cleaning and clean only those areas.
3. Brush away any loose dust, dirt and debris using soft/medium bristle tooth brush.
4. Make up a lather from the saddle soap and distilled water using small amounts of saddle soap. Use just enough to create a rich lather and apply the lather only to the soiled area using a clean soft sponge and a swirling motion. Rinse the sponge often and wring it out as completely as possible to release the accumulated soap and dirt. Repeat several times until soiling is minimized. Allow object to air dry in its normal shape. Do not force dry with hot air etc.

II. Preservation of Leather Artifacts:

1. Use the protector undiluted and apply with soft, lint free cloth such as cheese cloth. Apply sparingly so as not to soak leather. Apply to entire object and allow to air dry for approximately 2 hours Lay out in natural shape to dry.
2. Repeat this procedure.

III. Feeding Leather Artifacts:

1. Item should be clean and devoid of all loose dirt, dust etc.
2. Use soft, lint free cloth (cheese cloth) and apply sparingly to entire object.
3. Allow object to absorb the dressing for approximately 2 days.
4. Repeat procedure.
5. After absorption and drying of second cloat. Buff the object lightly with a soft lint free cloth to impart sheen and seal leather.
6. Metal fixtures may be sealed with lacquer (Acrylic) if deemed necessary. The metal should be cleaned of all verdigris, rust, etc. by using re-worked dental pick or probes. Any dressing on metal should be removed with Q-tips and Naptha. Lacquer will not stick to oily surfaces. Apply the lacquer with a small artists brush. Be careful to apply only to the fixtures and not the leather.
7. Allow lacquer 1-2 day drying time before storing or exhibition.

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