I have posted this before, but here goes again, as I feel it bears repeating, from an in depth study
"A comparative study on surface treatments in conservation of dry leather, with focus on silicone oil" by Lena Ludwick, Institution for Culture Göteborgs University 2012:28
3.3 Dressings
Dressings, or finishes, are usually oil or wax based and surface applied with the intent to restore flexibility, protect from deterioration and enhance appearance. For a long time, dressings used to be the standard treatment used in conservation of leather. This has since proved to be the cause of many problems, as there are a myriad of drawbacks with dressings as a conservation method. Since the base components are fatty substances, overuse can cause oxidization and stiffening, discoloration and staining, a tacky surface that attracts dust and dirt, encouraging of micro organism-growth, and hampering of future conservation efforts. Overapplying can also result in the depositing of spew on the surface, a white substance of free fatty acids, sometimes looking like mold. As well as oils and waxes, dressings often include some type of solvent. These bring with them potential problems of their own, such as dissolving of original surface treatments, adhesives or paint and wetting, swelling and deforming. (Kite et al., 2006, pg. 128) Despite these drawbacks, dressings are still commonly used,(Sturge et al., 2006, pg. 268, 273, 274, 278 & 286), mainly due to aesthetic reasons, giving the object a finished look.(Angus et al., 2006, pg. 115) Two of the dressings most often mentioned in literature are.... presented below.
Pliantine (British Museum Leather Dressing, BML) Microcrystalline wax, such as Renaissance wax polish.
From the National Park Service 1996 Museum handbook Part 1
Appendix S: Curatorial Care of Objects Made From Leather and Skin Products
3. How do I clean objects? The degree to which each soiled object can be cleaned is a function of the nature of the soil and the sensitivity of the object. Clean an object only as necessary to remove airborne soil accumulation.
Don't directly apply chemical reagents such as cleaners, dressings, waxes, and coatings: they are not beneficial and will complicate future conservation treatment.
You can't remove some surface soils by simple cleaning methods, and other soils are not removable at all. Highly deteriorated objects cannot be cleaned by routine procedures so degraded surfaces should be noted and protected so that cleaning will be avoided. S:14 NPS Museum Handbook, Part I (1996) When decorative elements on an object are extensive and very delicate, refer cleaning to a professional conservator. Surfaces that have specialized finishes also may require exemption from cleaning. Figure S.5 describes cleaning techniques that can be considered for objects in good condition. 4. How do I handle skin and hide materials? Much of the damage caused to leather and skin products is due to improper handling. Therefore, you need to train staff in proper handling techniques. See MH-I, Chapter 6, Handling, Packing, and Shipping Museum Objects, for general handling rules. In addition to the general rules there are a few essential rules for the safe handling of these objects: • Be prepared before handling these objects by having a clean area ready to receive the object. Arrange for assistance from others when necessary. • Consider the weight of the entire object before lifting; aged and deteriorated fibers cannot tolerate much physical stress. Avoid suspending, creasing, and folding items. • Move leather and skin artifacts on a tray support, in a drawer, or in a box; if direct handling is necessary, use both hands and support the object from underneath, not from original handles and straps. • Accommodate the special handling requirements of appendages and decorative elements such as beadwork and dangles. • Handle skin and hide materials only while wearing clean, cotton gloves; if hand contact is required, wash hands just before handling.
I will post the current approved method of treating antique leather when I get back to my home computer.
From Texas A&M Department of Anthropology's Conservation Manual:
TREATMENT OF BRITTLE and/or DESICCATED LEATHER
The following treatments that involve the addition of lubricants have been used successfully on brittle and/or desiccated leather.
Glycerol, which is soluble in water and alcohol, acts as a humectant for the leather.
SMITHSONIAN GLYCERIN TREATMENT
59 percent glycerin (glycerol)
39 percent water
1 percent formaldehyde or 1% Dowicide (TM) 1
OR
25 percent glycerin
75 percent alcohol
Immerse the artifact in the solution until the leather is pliable. (When an alcohol solution is used, it is difficult to determine when
the leather is pliable because the alcohol makes the leather stiff.) Treatment may require several weeks. The treatment restores
flexibility, but glycerin is hygroscopic and can support mold growth. In spite of this fact, the Smithsonian Glycerin Treatment has been
used successfully.
Waterlogged leather recovered from excavations by The Museum of London is conserved in a solution of 30 percent glycerin and
70 percent alcohol (ethanol) for two weeks. The leather is then dried in three successive baths of acetone, each three hours long
(glycerin is not soluble in acetone). Similar results can be achieved by using 10-40 percent glycerin mixed in 90-60 percent alcohol or
water. Avoid using concentrated glycerin. While the solutions in alcohol can remove tanning agents, alcohol speeds up the
conservation process and confers greater mechanical strength to the leather than will a water solution.
The glycerin treatment has also been applied to basketry, matting, sandals, etc. to restore pliability, quite often with disastrous
results. It should be kept in mind that there is no reason to make something flexible or pliable if it was not particularly pliable in the
first place. The glycerin treatment can be used in combination with PEG. To retreat any object that was conserved with glycerin, such
as basketry, remove the glycerin with successive changes of alcohol baths.
BRITISH MUSEUM LEATHER DRESSING TREATMENT (BML)
200 gm (7 oz) anhydrous lanolin
30 ml (1 oz) cedarwood oil (acts as a fungicide)
15 gm (½ oz) beeswax (optional)
350 ml diethyl ether (B.P. 15-25°C) or 330 ml of hexane
Heat the first three items together (beeswax can be omitted, its function is to act as a polish) and then pour the molten liquid into
the ether or hexane. Allow to cool while constantly stirring. Exercise extreme caution, as ether and hexane have low boiling points and
are very flammable. Apply sparingly to the leather and rub well. Wait two days, then polish the treated leather with a soft cloth. Very
hard leather can be soaked in a solution of one part BML: three parts Stoddards Solvent. BML darkens the leather, but it is a
treatment with a good success record.
POLYETHYLENE GLYCOL (PEG) TREATMENTS
Dry leather can be saturated with water or alcohol and treated with PEG 1450, PEG 540 Blend, PEG 600, or PEG 400. In the past,
leather was treated in PEG which was heated to a temperature of 40-50°C. Presently, most leather treatments are carried out at room
temperature because heat is generally detrimental to leather.
The PEG treatment consists of immersing leather in a dilute solution of PEG ( i.e., 10 percent) in water or alcohol and increasing
the PEG concentration in 10 percent increments as it is absorbed by the leather. A final PEG concentration of 30 percent in solution is
adequate for most archaeological leather. Keep the artifact immersed in the 30 percent PEG solution for several days until the leather
is flexible. Once pliable, remove from the solution and clean off excess PEG from the leather with toluene or water. Allow treated
leather to dry slowly under controlled conditions.
As mentioned in previous chapters, there are several types of PEG, and each has its own characteristics. PEG 540 Blend (equal
parts of PEGs 1450 and 300) is slightly hygroscopic and becomes moist at high humidity; for this reason, the surface of the leather
treated with PEG 540 Blend is sometimes sealed with a hard wax, i.e., a mixture of 100 gm microcrystalline wax and 25 gm
polyethylene wax. PEG 3250 is very hard and is not very hygroscopic. Its main disadvantage (in some cases advantage) is that the
treated leather is rigid. When using PEG 3250, form the treated specimen to its final shape while the wax is still warm and then allow
the artifact to cool. PEG 1450 gives consistently good results. The various PEG treatments are more commonly used for the
conservation of dry leather. A 15 percent PEG 400 solution is commonly used as a pre-treatment when the leather is to be freeze
dried.
PEG-treated leather can be hygroscopic, greasy, and dark in color. There is the additional possibility that the PEG may eventually
migrate out of the leather.
BAVON TREATMENT
Bavon ASAK 5205 is a water-soluble emulsion, while Bavon ASAK ABP is solvent-soluble emulsion. The exact chemistry of Bavon is
unknown. In some sources, it is described as being an alkylated succinic acid-mineral oil blend. Bavon ASAK-ABP is described as
being a copolymer of polyhydric alcohol and a partial ester of an unsaturated hydrocarbon. In archaeological conservation, Bavon
works as a lubricant that makes leather pliable and gives it a natural brown appearance.
Very hard, desiccated leather has been successfully softened by soaking it in a concentrated Bavon leather dressing consisting of
six parts Bavon ASAK ABP to four parts 1:1:1 trichloroethane. Soak until satisfactory pliability is reached, then place the leather
between blotters and glass and allow it to dry.
TREATMENT OF WET OR WATERLOGGED LEATHER
Leather, like a lot of organic material from a marine environment, undergoes some complex changes in a marine environment
(Florian 1987). The difficulties in achieving natural looking, chemically stable results have long been known by conservators (Jenssen
1983). The best review of the most common treatment currently in use is presented by Jenssen (1987). The most relevant treatments
are discussed. below.
Waterlogged leather should be stored in water with 0.1 percent Dowicide 1 prior to treatment. If the leather is to be treated in an
organic solvent, the leather can be stored in 50 percent water/50 percent ethanol or straight ethanol; a fungicide is not required.
Treated leather should not be stored in an environment with a relative humidity higher than 63 percent.
POLYETHYLENE GLYCOL (PEG) TREATMENTS
Treat with the method described above for desiccated leather, using PEG 400, 540 Blend, 600, 1450, or 3350. Gradually increase the
concentration of PEG in solution up to 30-100 percent. Treatments with aqueous solutions of PEG are slower processes but are less
expensive than treatments involving solvent solutions. Some conservators prefer alcohol treatments, while others think that alcohol
treatments cause the leather to shrink more than comparable aqueous treatments. Solvent solutions, however, produce a lighter
leather with more uniform shrinkage. All the PEG treatments for waterlogged leather are satisfactory by themselves, but treatment is
considerably enhanced if the leather is taken through a final step of freeze drying. The freeze-drying process is identical to that
described earlier for wood. A commercial freeze-drying vacuum chamber works the best; however, very good results have been
obtained using domestic chest freezers. The former takes only a week or so, while the latter may take several weeks. Progress can be
determined by regular weighing of the object to determine weight loss as the leather loses moisture.
BAVON TREATMENT
1. Wash leather in a 1 percent solution of Lissapol, castile soap, soft soap, or saddle soap; never use commercial detergents on
leather as they may extract tanning materials.
2. If iron stains are present, they can be removed by immersing the leather in a solution of tap water and 3-10 percent disodium
EDTA (pH 4) or 3-5 percent ammonium citrate (pH 5) for a maximum of one hour (shorter if possible). EDTA has been
reported to damage fibers of leather but is relatively safe if used selectively and cautiously. Ammonium citrate is recommended
over disodium EDTA by the Canadian Conservation Institute.
3. If calcareous material is present, place the leather in a 2 percent hydrochloric acid solution for up to one hour.
4. Rinse the leather thoroughly in running water for 30 minutes to lower the pH to 3-6 or to the pH of the rinse water.
5. Dehydrate the object in acetone. Use two or more successive hour-long baths.
6. Air dry until the leather is supple, then place between absorbent tissue and glass to dry for 24 hours.
7. Apply Bavon leather dressing (below) with a brush. Flex and manipulate leather during the application of the Bavon.
Bavon Leather Dressing
1 liter of stabilized 1:1:1 trichloroethane
1 gram Dowicide 1
50 grams anhydrous lanolin
20 grams Bavon ASAK-ABP
GLYCERIN TREATMENT
Waterlogged leather recovered from excavations by The Museum of London is conserved by placing it in a solution of 30 percent
glycerin and 70 percent alcohol (ethanol) for two weeks. The leather is then dried in three three-hour long baths of acetone (glycerin is
not miscible in acetone and is, therefore, not removed in the acetone baths). Good results can also be achieved with a solution of 10-
40 percent glycerin mixed in 60-90 percent alcohol or water.
FREEZE DRYING
Freeze drying is the best method for conserving waterlogged leather. The leather is first immersed in a 15 percent solution of PEG 400,
which acts as a humectant and prevents excessive shrinkage (a fungicide, such as 1 percent boric acid should be mixed with the PEG
solution). After immersion, the object is frozen to -20 to -30°C. Like biological specimens, a quick freeze is best. This can be achieved
by immersing the leather in acetone with dry ice (frozen CO2). The piece is then placed in a freeze-drying chamber under vacuum for
a period of two to four weeks. Some acceptable results have also been had using non-vacuum freeze drying in a (preferably frost-free)
freezer chest.
DEHYDRATION USING ORGANIC SOLVENTS
This treatment involves the replacement of water in leather with a water-miscible organic solvent. In most cases, a sequence of
solvents with decreasing polarity is used, e.g., a series of baths of x percent water/x percent of isopropanol, followed by a bath of 100
percent isopropanol, a bath of 100 percent ethanol or methanol, 100 percent methyl ethyl ketone, 100 percent acetone, and finally 100
percent ether. Slow desiccation of glutinous collagen fibers allows their surfaces to become less sticky and less brittle and thus more
flexible. This example is a very conservative method of treatment. In most instances, fewer baths are used and for some leather,
drying only through acetone is necessary. The following solvent dehydration treatment, described by Plenderleith and Werner
(1971:34), allows the leather to dry out in a flexible condition without undue shrinkage.
1. Remove iron stains with 5-10 percent disodium EDTA (pH 4).
2. Rinse the leather in clean water, brush lightly.
3. Remove excess water by soaking the object in methyl ethyl ketone or acetone.
4. Immerse the object in carbon tetra-chloride with a fungicide, such as oxide of naphthenate.
5. Dry between blotting paper and glass plates.
6. Apply leather dressing and work the leather into shape if necessary.
Of the treatments discussed above, solvent-drying treatments followed by the application of a leather dressing are the most
effective. Controlled air drying from an aqueous state never works. The contractile forces of the escaping water draw the protein fibers
together, causing the leather to harden and shrink. Some conservators prefer freeze drying with a pre-treatment of PEG 400. These
are the two most common treatments, and both can give acceptable results, but there is always the problem of the leather feeling
greasy, overly stiff, and/or too dry and brittle when treated by any of the methods now in general use.
SILICONE
Bringing the