New Jersey Scuba Diving
Conservation of Bone, Ivory, Teeth, & Antler
Approximately 70 percent of bone and ivory is made up of an inorganic lattice composed of calcium phosphate and various carbonates and fluorides. The organic tissue of both bone and ivory is ossein and it constitutes at least 30 percent of the total weight of the material. It is often difficult to distinguish between bone and ivory unless the material is examined microscopically. Bone is coarse grained with characteristic lacunae or voids; ivory is a hard, dense tissue with lenticular areas. Both bone and ivory are easily warped by heat and moisture and are decomposed by prolonged exposure to water.
In archaeological sites, ossein is decomposed by hydrolysis, and the inorganic framework is disintegrated by acids. In waterlogged sites, bone and ivory can be reduced to a sponge-like material; in arid sites, they become dry, brittle, and fragmented. In some circumstances, bone and ivory can become fossilized as the ossein is replaced by silica and mineral salts. Archaeological bone and ivory can only be cleaned, strengthened, and stabilized; satisfactory restoration is often impossible.
REMOVAL OF SURFACE DIRT
- Wash with soap and water or alcohol ( the use of alcohol will facilitate drying ). Towel dry.
- When washing with water, limit amount time in water.
- Brush lightly with brushes and/or lightly scrape with wooden, plastic or metal tools. Dental tools are particularly useful for this purpose.
Note: Structurally weak bone or ivory must be cleaned carefully and the cleaning method used should be dictated by the specimen's condition.
REMOVAL OF SOLUBLE SALTS
Bone or ivory from a salty environment will invariably absorb soluble salts which will crystallize out as the object dries. The action of salt crystallization will cause surface flaking and can, in some cases, destroy the specimen. The soluble salts must be removed in order to make the object stable. For faunal bone, it is usually not necessary to remove all the soluble salts. It is most efficient to rinse faunal bone in tap water until the chloride level in the material being treated equalizes that of the tap water. For more important artifacts made of any of these materials it advisable to remove all the soluble salts by rinsing for an appropriate length of time in tap water and then in deionized water.
- If the bone/ivory is structurally sound, the salts can be diffused out by rinsing in successive baths of water. While faunal bone can be put directly into fresh water from seawater ( there is a slight chance of cracking ), the following succession of baths is recommended for important artifacts:
100 percent sea water ? 75 percent sea water/25 percent fresh water ( local tap water ) ? 50 percent sea water/50 percent fresh water ? 25 percent sea water/75 percent fresh water ? straight fresh water.
The object then goes through either running water rinses or numerous changes of the bath water until the soluble salt level reaches that of the tap water or the water supply being used. De-ionized or distilled water is then substituted for the fresh water bath until the soluble salts are removed or reaches an acceptable level.
In order to determine the level of salts in the rinse water, it is necessary to use a conductivity meter. In most cases, one can alternatively use the silver nitrate test to detect the presence of sodium chloride. When sodium chlorides are no longer present, it is reasonable to assume that the bulk of the soluble salts has been removed. The conductivity meter measures the presence of all soluble salts and is thus a much more reliable indicator of the presence and absence of soluble salts in an aqueous solution.
- If the bone/ivory is structurally unsound, it can be consolidated with a 5 percent solution of Acryloid B-72 and then rinsed. The soluble salts will diffuse through the resin, albeit much more slowly, during the rinsing treatment.
- Dry bone/ivory in series of alcohol baths ( 50 percent alcohol/50 percent water, increasing the alcohol content of the baths to 90 percent, 100 percent, and a final bath of 100 percent alcohol ). For teeth and ivory, it is sometimes necessary to go through longer dehydration baths in order to ensure that the surface of the material being treated does not delaminate or crack. In such cases, a recommended series of dehydration baths should begin with straight water, followed by 95 percent water/5 percent ethanol ( only water-miscible solvents should be used ); an additional 5 percent ethanol should be then added to the bath until the artifact is in straight ethanol. To further ensure the integrity of the surface, the artifact should be placed in a second and even a third bath. The object can then be taken through two baths of acetone. In a few exceptionally critical cases, it may be advisable to take the object through at least two baths of diethyl ether. In most cases, after the object has been taken through two baths of acetone, it is reasonable to assume that all the water has been removed. The object should be then consolidated with a proper resin in order to strengthen it and to make it less susceptible to fluctuations in atmospheric humidity ( see below ).
REMOVAL OF INSOLUBLE SALTS AND STAINS
If it is necessary to remove insoluble salts or stains from bone/ivory, some means of mechanical removal using picks or other tools is always recommended over any chemical treatment. Inevitably, some damage is done to bone and related material when stains and insoluble salts are removed by chemical means. When chemical agents are used, always make sure that the material is thoroughly wetted with water before any chemical is applied. This ensures that the treating chemical remains on the surface of the artifact and is not absorbed.
- Calcium carbonate stains: Structurally sound bone can be immersed in 5 - 10 percent solutions of hydrochloric acid or formic acid. Monitor process closely.
- Iron stains: 5-10 percent oxalic acid has been used to remove iron stain stains from bone. For stubborn stains, 5 percent ammonium citrate used alone or 5 percent ammonium citrate followed by 5 percent oxalic acid are effective treatments.
- Sulfide stains: 5-10 percent hydrogen peroxide is used to remove sulfide stains. Stained bone may be placed in a hydrosulfite solution followed by dilute hydrogen peroxide to remove any remaining stain.
Unsound bone should be treated with localized applications of the solution with a brush or swab. If unsound bone is submerged, the evolution of carbon dioxide from the decomposition of the CaCO3 will break up the specimen. Very fragile bone may require that the acid be applied locally to stubborn spots, scraped, and blotted; repeat all steps until the area is cleaned.
Following stain removal, it is necessary to rinse the artifact in water to remove all residue of the treating chemical, dry in alcohol baths, and then consolidate with a resin as described below.
Any resin solution must be diluted to decrease the viscosity and increase its ability to penetrate the material being treated. A 5-10 percent solution of a suitable transparent synthetic resin may be used. When large amounts of faunal bone need to be consolidated, satisfactory results are achieved with water soluble Elmer's Glue All. When bone, ivory, or teeth are treated, slowly dehydrate them in organic solvents as described above then consolidate them with PVA ( V7 ) or Acryloid B-72. The use of PVA V7 is encouraged because while the molecules are smaller and are able to penetrate denser material, the resin has enough resilience to mechanically strengthen any object treated with it. For less dense material and large amounts of faunal bone, PVA with a viscosity of V15 is recommended, since it is a stronger, general-purpose resin.
For surface consolidation, apply resin by brush. Good results can be obtained by applying a light coat of resin, allowing it to dry, and then applying a second coat. This procedure should be repeated several times in order to allow for sufficient resin to be absorbed by the material. Complete immersion of the artifact in the consolidating resin gives excellent results, while complete immersion of the artifact in the resin under a vacuum is considered the best method for consolidating most bone or ivory artifacts.
The type of glue used to glue bone, ivory, or teeth together is to some degree dependent upon how the object was treated. If the bone or related material has been consolidated with a resin, a thick viscous mixture of the same resin should be used. PVA with a viscosity of V25, Acryloid B-72, PVA emulsions such as Bull Dog, and in some cases, Elmer's Glue All, are also serviceable glues.
SEEDS AND PLANT MATERIAL
Miscellaneous seeds and plant material are, for all intents and purposes, treated in much the same way, if not exactly the same way, as described above for bone and related material. Once recovered, it necessary to rinse the material to remove any soluble salts that may be present, mechanically clean any material requiring it, chemically treat the material, and rinse out the treating chemical. The material should be dried in a series of water/water-miscible alcohol baths and then consolidated.
The conservation of waterlogged bone and ivory, as well as most plant material, is a straight-forward process. Complex problems seldom arise, except in cases where bone is so badly deteriorated that it is cannot be treated. In general, intensive rinsing in water to remove the soluble salts followed by complete dehydration through a graded series of water-miscible solvents, and consolidation with an appropriate resin is all that is required. Stains can be removed, but the process may damage bone if care is not taken. The only equipment required is appropriately sized containers, a selection of resins, and a variety of solvents.
Conservation of Leather
As with all porous material, it is necessary to remove the bulk of the soluble salts present in leather recovered from marine environments. The procedure is the same as that described earlier for bone and ceramics. Prior to conservation, archaeological leather must be washed in order to remove any ingrained dirt. Ideally, leather should be washed in water alone. A variety of mechanical cleaning techniques may be required, depending upon the condition of the leather and the particular cleaning problem. Soft brushes, water jets, ultrasonic cleaners, and ultrasonic dental tools are effective mechanical cleaning tools for leather. If chemical cleaning is necessary to remove ingrained dirt, a small amount of non-ionic detergent ( about a 1 percent solution ) or sodium hexametaphosphate may be used. If Calgon ( a commercial water softener ) is used, first ensure that the pH is between 3 and 5; the addition of additives may make it unsafe to use on leather. Rinse the leather well after washing. Do not use any chemicals that will damage the leather's collagen fibers.
A safe storage solution for waterlogged leather, or any organic material for that matter, can be made by preparing a stock solution of 50 percent water / 50 percent ethanol. To the solution, add 10 percent glycerin by volume and two to three drops of formaldehyde.
The conservator should always keep in mind that it is often better to leave stable stains on the leather than to damage the leather by trying to remove them. For stain removal, particularly iron staining, 3-5 percent ammonium citrate or ethylene-diamine-tetraacetic acid ( disodium EDTA ) is used. Commercial trades names for EDTA are Titriplex III and Disodium Deterate. Soak for two to three hours while monitoring closely, then rinse the piece in running water or standing tap water until all chemical residues are removed. Check the pH of a standing bath of water containing the leather to determine if the chemical removal is complete. Always keep in mind that chemicals used to clean rusts and mineral concretions ( e.g., oxalic acid, EDTA ) may produce further hydrolysis of the proteinaceous collagen fibers in the leather. Furthermore, they may remove tanning and/or coloring agents, painted decorations, and other attributes that are part of the diagnostic attributes of the leather object. Caution should be exercised when using any of these chemicals on leather, as diagnostic attributes should never be removed.
Freeze drying and solvent dehydration are the most common conservation treatments for waterlogged leather. The drying behavior of any piece of leather, however, is dependent upon its condition at deposition, the burial environment, the genus, species, health, and sex of the individual ( man or beast ), the location of the skin on the body, the production or tanning method used, and finally, the leather object's history. Very good results have been achieved in the conservation of bog bodies through freeze drying using 15 percent PEG 400. The PEG acts as a lubricant to minimize skin and bone shrinkage during drying.
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
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 ( ? 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 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.
- 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.
- 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.
- If calcareous material is present, place the leather in a 2 percent hydrochloric acid solution for up to one hour.
- 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.
- Dehydrate the object in acetone. Use two or more successive hour-long baths.
- Air dry until the leather is supple, then place between absorbent tissue and glass to dry for 24 hours.
- 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
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 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.
- Remove iron stains with 5-10 percent disodium EDTA ( pH 4 ).
- Rinse the leather in clean water, brush lightly.
- Remove excess water by soaking the object in methyl ethyl ketone or acetone.
- Immerse the object in carbon tetra-chloride with a fungicide, such as oxide of naphthenate.
- Dry between blotting paper and glass plates.
- 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.
The process of treating waterlogged leather with silicone oil is very similar to the treatment outlined for waterlogged wood. In the treatment of waterlogged leather, however, best results are obtained when the catalyst is painted onto the surface of the leather after it has been saturated with silicone oil and a crosslinker.
Conservation of Textiles
The term 'textile' is applied to woven objects and also to fabrics which are the products of other kinds of interlacing of yarns, such as braiding, looping, knitting, lace making, and netting. The textile category also includes materials such as felts and non-woven materials in which the fibers gain coherence by a process other than spinning.
This brief discussion of textile conservation is limited to the natural fibers of animal and plant origin: wool, hair, silk, cotton, flax, jute, hemp, nettle, grass, etc. The animal fibers consist primarily of protein and are more resistant to decay than vegetable fibers, which are composed primarily of cellulose. Flax and cotton, for example, are very susceptible to attack by bacteria under humid conditions and seldom survive in archaeological environments. All textiles are deteriorated by light, insects, microorganisms, and air pollution which, alone or together, cause considerable loss of tensile strength and pliability. The oxygen in the atmosphere affects all organic substances to varying degrees. Prolonged exposure to normal atmospheric conditions will cause textiles to weaken and disintegrate. The speed of the deterioration varies according to environment and the nature of the fibers. The main factors that promote the decay of textiles can be categorized into three groups:
- Organic: Because textiles are organic, they are subject to attack by molds and bacteria. Decomposition is greatest in situations that favor the growth of these organisms, such as damp heat, stagnant air, and contact of the material with vegetable matter. Attack by destructive insects may also be encountered.
- Physical: Excessive heat causes desiccation and embrittlement; exposure to ultra-violet light causes a type of deterioration known as 'tendering, ' as well as the photochemical degradation of susceptible dyes.
- Chemical: Exposure to noxious gases can also cause tendering. In some cases, these gases are converted to acids, which are the main cause for the deterioration of some textiles.
In general, textile conservation should be left to specialists; however, many archaeological specimens can be treated even by novice conservators. Fibers that compose a fabric should be identified before any treatment is undertaken, particularly if stain removal is required. Physical tests, such as burning, quickly identify the presence of animal fibers, which do not burn readily and shrivel into a residue of carbon. These fibers usually emit the distinct odor of singed hair. Vegetal fibers burn easily to a fine ash. Many fibers and hairs can also be readily identified by microscopic examination. Animal hairs, for example, can be identified by their characteristic cuticle patterns and medullar cross sections. Simple staining tests enable the conservator to distinguish between the different kinds of fibers.
The textile materials encountered most often in archaeological sites are linen, cotton, wool, and silk. Linen is a spun and woven vegetable-based fiber derived from flax stalks and branches. Linen fibers lie close together and are durable. They withstand moderate alkaline conditions because of their cellulose content, but are readily affected by acids. Moisture easily passes through the fibers of linen, causing the material to undergo dimensional and weight changes as well as changes in the overall strength. Linen does not take dye well and is usually left in a bleached or unbleached white state.
Schematic drawing of flax.
Cotton is a vegetable fiber derived from lint on the cotton seed. It can survive in moderate alkaline conditions but is adversely affected by acids. Cotton does not transmit moisture like linen and is very absorbent in its processed state. It is this characteristic which allows cotton to take dyes well. Cotton has a very characteristic clockwise twist; for this reason, it is commonly spun in a 'Z' twist.
Schematic drawing of cotton.
Wool consists of protein fibers. The majority of the amino acids in the protein of the wool are keratin, which contains insect-attracting sulfur. Wool fibers absorb more moisture and accept dyes better than vegetable fibers. Wool is not a strong fiber and weakens considerably when wet.
Schematic drawing of wool.
Silk is an animal ( insect ) fiber that is derived from the cocoon filament of the silkworm. Because it is basically protein, silk is easily affected by alkalies and various inorganic acids. Like wool, it easily absorbs moisture and will take dyes readily. These dyes, however, are not as light-fast as those on wool. Silk is as strong as a steel wire of the same diameter but is very light sensitive. Therefore, it will break down faster than wool when exposed to ultra-violet rays.
Schematic drawing of silk.
The proper treatment of textiles usually requires the use of flat, shallow pans, hot plates, and racks, or other devices that can support fragile textiles during rinsing, treatment, and drying. Treatment involves documentation, cleaning, reinforcing, sterilization, and proper storage and protection from environmental dangers.
A thorough documentation, both photographic and written, should record all pertinent information about the textile to be treated. The various features and properties that the conservator should look for are:
- The nature of the fibers
- The spin of the yarn ( i.e., 'Z' or 'S' twist )
- The number of wefts and warps per inch ( or centimeter )
- The type of weaving and of dye ( water-fast or soluble )
- metal threads, and any other features that may be diagnostic or of interest.
CLEANING TO REMOVE SOIL, DISCOLORATION AND STAINS
A great number of substances can be removed from textiles by simply washing the artifact in water. De-ionized water is always preferred. Add 0.4 to 1 percent ammonium hydroxide ( 0.4 percent for animal fiber, 1 percent for vegetable fibers ) to the water for greater cleansing power. If necessary, add 1 percent neutral non-ionic detergent ( such as Lissapol N ) to remove more stubborn soil. During the washing and cleaning process, the fabric can be bleached in a 4 percent hydrogen peroxide solution. For more stubborn stains ( including mildew, mold, black sulfide stains, and organic stains ), soak the artifact in one of the following solutions:
Stain Solution 1
- 1 liter de-ionized water
- 60 ml 30 percent hydrogen peroxide
- 2.5 g sodium silicate dissolved in 100 ml hot de-ionized water
Stain Solution 2 ( for more stubborn stains )
- 1 liter de-ionized water
- 300 ml 30 percent hydrogen peroxide
- 20 g sodium silicate
- 5 g sodium carbonate
- 5 g sodium hydroxide
Soak for ? to 1 hour or until the stain is removed then place the artifact in a closed bag to oxidize.
Sodium silicate and metasilicate are stabilizers, which are added to control the decomposition of hydrogen peroxide ( H202 ) to water ( H20 ). Whenever possible, a simple solution of hydrogen peroxide ( and possibly a stabilizer ) is recommended for stain removal because as the hydrogen peroxide loses oxygen, it bleaches and converts to water. Therefore, there is no danger of continuing chemical action. Hydrogen peroxide can be used on all vegetable fibers and its bleaching effect is permanent. Do not use hydrogen peroxide on hair or any fiber that was not white when originally in use. The addition of different sodium or alkali compounds are used to control the pH and to increase the cleaning power of the solution.
Copper corrosion stains can be treated with 1-5 percent ammonium hydroxide. For silver corrosion stains, first soak the stain with potassium cyanide then apply a few drops of iodine. Remove the resulting silver iodide product with a 5 percent solution of sodium thiosulfate. Textiles with iron rust stains can be treated with any of the following chemical solutions:
- 5 percent hydrochloric acid [muriatic acid ( HCL )]
- 5 percent oxalic acid ( COOH )2
- 10 percent hydrofluoric acid ( HF )
- 5 percent EDTA disodium
- 5 percent acetic acid ( CH3COOH )
- 5 percent formic acid ( HCOOH )
- 2-10 percent ammonium citrate
Oxalic acid and hydrofluoric acid solutions are the most effective for removing iron stains from archaeological textiles. Extreme caution must be taken, however, when handling hydrofluoric acid. EDTA disodium and ammonium citrate solutions are often recommended because their higher pHs ( >2.5 ) potentially do less damage to fibers. These solutions are effective but rather slow. After any chemical treatment, intensive rinsing in de-ionized water will remove all residue from the textile which may adversely affect the fibers over time.
For textiles that cannot be cleaned with water ( such as textiles with water-soluble dyes ), dry cleaning using organic solvents, such as perchlorethylene or trichlorethylene, or petroleum solvents, such as white spirits, is recommended. The advantages of solvent cleaning are:
- Unlike water, solvents do not soften textile fibers, minimizing the risk of shrinkage and loss of shape.
- Dyes not fast in water may be undisturbed in solvent.
- Solvents are more efficient than water for dissolving grease.
- In general, solvents are volatile and dry quickly.
The costs of solvent cleaning are much higher, and the problems of toxicity and inflammability must be taken into consideration.
REINFORCING FRAGILE TEXTILES
Quite often, the only practical method of reinforcing fragile textiles is to fasten them to a synthetic mesh of terylene, light cotton fabric, fiber glass, or other substance. Particularly fragile textiles are sometimes mounted between sheets of plastic or glass. In most cases, a heat-sealable adhesive, such as polyvinyl acetate, polyvinyl alcohol, Acryloid B-72, or their emulsions, are used to coat the backing which is then ironed ( heat-sealed ) onto the textile. Any breaks in the threads either in the warp or weft of the material should be affixed with drops of glue to prevent additional unraveling
The conservator also has the option to consolidate and reinforce fragile textiles with various synthetic resins. Since water softens and makes textile fibers pliable, emulsions and water-soluble resins are preferred for textile consolidation. Water-based adhesives also give the conservator more 'working time' than solvent-based adhesives. The most frequently recommended resins for textile conservation are:
- polyvinyl alcohol ( water-soluble, dries clear with minimum shrinkage )
- polyvinyl acetate ( V7 ) ( note: resin shrinkage during drying may distort fibers )
- ethulose ( ethyl-hydroethyl cellulose ) ( water-soluble, very pliable )
- Acryloid B-72, 5 percent in toluene
A mixture of 0.15 percent ethyl-hydroethyl cellulose, 0.6 percent polyethylene glycol ( PEG ) 400, and 0.2 percent fungicide will consolidate fragile fabrics and restore moisture to dry, brittle fibers. A solution of 20 percent lanolin in toluene can be applied to fibers that have a tendency to shred or lint.
For wholesale treatment of mold and insect infestation, place the infested objects in a closed container with thymol crystals. The crystal can be vaporized by holding the container over a light bulb. After treatment with thymol crystals, spray the objects with a 0.5-1 percent Lysol solution. This treatment will remedy most problems. Carbon disulfide can also be used as a fumigation agent.
Disinfectant solution can be prepared in the lab by mixing 0.1 percent Dowicide 1 ( ortho-phenylphenol ), 68 percent ethanol, and 30 percent de-ionized water. This solution is lethal to most bacteria, fungal spores, and surface mildews. Dowicide 1 has a maximum solubility of 0.1 percent in water and 46-58 percent in the various alcohols. Alternatively, a solution of 2 percent DowicideA and sodium ortho-phenylphenate can be used. Dowicide A has a maximum solubility of 120 percent in water and approximately 350 percent in alcohol. For the majority of textile disinfectant needs, Lysol disinfectant spray will suffice. Lysol spray consists of 0.1 percent Dowicide1, 79 percent ethanol, 8 percent n-alkyl, and 0.035 percent n-ethyl morpholinium ethylsulfates ( deodorizers and scents ). The conservator should keep in mind that topical treatments are not long lasting.
CONSERVATION OF WATERLOGGED CANVAS AND ROPE
After a series of tests by the Conservation Division of the Western Australia Museum on artifacts recovered from a 19th-century shipwreck, the following sequence of treatment was proposed for the conservation of canvas ( and other similar fabrics ) and rope.
- Immerse artifact in 10 percent hydrochloric acid to remove all adhering encrustation and some iron corrosion and stains.
- Rinse artifact in running water. Watch for any dyes that may be adversely affected.
- Soak artifact in acetone to remove any tar, pitch, tallow, or other acetone-soluble substances. Watch for any dyes that may be removed.
- Soak artifact in 5 percent oxalic acid to remove the bulk, if not all, of the iron stains. Treatment time will vary from a couple of hours to a couple of days.
- Immerse artifact in 5 percent EDTA disodium to remove any remaining iron stains. Soaking time will vary from a couple of hours to up to three days.
Note: Both Steps 4 and 5 may be required for particularly stubborn iron stains. In other instances, either Step 4 or Step 5 may be used.
- Bleach artifact in a 5 percent hydrogen peroxide solution. Particularly stubborn stains may be treated for short periods in a stronger ( 10-20 percent ) solution. Perform this step only on cloth, canvas, and textiles that were originally white. Never use hydrogen peroxide on animal fibers.
- Rinse artifact thoroughly in de-ionized or distilled water.
- Dehydrate artifact in acetone and air dry.
- If necessary, consolidate the material with a suitable synthetic resin. In some cases, the textile may have to be treated with heat-sealable resin and either dry mounted or sealed to a backing of another fabric, such as light cotton or a synthetic mesh.
SILICONE OIL TREATMENT OF WATERLOGGED TEXTILES AND ROPE
Waterlogged textiles and rope are currently being conserved using silicone oil. The results have been quite promising. See the Archaeological Preservation Research Laboratory Reports.
Store textiles in an environment that limits their exposure to atmospheric pollutants and ultra-violet light. Relative humidity should be kept at a maximum of 68 percent. ( Environments with a relative humidity of over 70 percent encourage mold growth. ) Ideally, textiles should be stored in a dark place with a low temperature of 10°C and a relative humidity of 50 percent or less. Moths and other insects should be deterred by keeping moth balls ( paradichlorobenzene ) in the storage area. This is particularly critical when storing wool.
Donny L. Hamilton
1998. Methods of Conserving Underwater Archaeological Material Culture. Conservation Files: ANTH 605, Conservation of Cultural Resources I. Nautical Archaeology Program, Texas A&M University, World Wide Web, http://nautarch.tamu.edu/class/ANTH605/.
Copyright 2000 Donny L. Hamilton, Conservation Research Laboratory, Texas A&M University
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