Tanning , or hide tanning , is the process of treating skins and hides of animals to produce leather . A tannery is the place where the skins are processed.
62-439: Tanyard may refer to: The yard of a tannery, see Tanning (leather) Tanyard, Maryland , an unincorporated community Tanyard Branch (disambiguation) Tanyard Creek (disambiguation) Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with the title Tanyard . If an internal link led you here, you may wish to change
124-487: A lime kiln above 900 °C (1,650 °F) converts it into the highly caustic material burnt lime , unslaked lime or quicklime ( calcium oxide ) and, through subsequent addition of water, into the less caustic (but still strongly alkaline ) slaked lime or hydrated lime ( calcium hydroxide , Ca(OH) 2 ), the process of which is called slaking of lime . When the term is encountered in an agricultural context, it usually refers to agricultural lime , which today
186-550: A tannery . The English word for tanning is from medieval Latin tannāre , derivative of tannum ( oak bark ), from French tan (tanbark), from old-Cornish tann (oak). These terms are related to the hypothetical Proto-Indo-European * dʰonu meaning ' fir tree'. (The same word is source for Old High German tanna meaning 'fir', related to modern German Tannenbaum ). Ancient civilizations used leather for waterskins , bags, harnesses and tack, boats, armour , quivers , scabbards , boots , and sandals . Tanning
248-441: A bath solution containing vegetable tannins, such as found in gallnuts , the leaves of sumac , the leaves of certain acacia trees, the outer green shells of walnuts , among other plants. The use of vegetable tanning is a process that takes longer than mineral tanning when converting rawhides into leather. Mineral tanned leather is used principally for shoes, car seats, and upholstery in homes (sofas, etc.). Vegetable tanned leather
310-427: A high content of glycine , proline , and hydroxyproline , usually in the repeat -gly-pro-hypro-gly-. These residues give rise to collagen's helical structure. Collagen's high content of hydroxyproline allows cross-linking by hydrogen bonding within the helical structure. Ionized carboxyl groups (RCO 2 ) are formed by the action of hydroxide. This conversion occurs during the liming process, before introduction of
372-480: A large factor in how hazardous wastewater results in contaminating the environment. This is especially prominent in small and medium-sized tanneries in developing countries. The UN Leather Working Group (LWG) "provides an environmental audit protocol, designed to assess the facilities of leather manufacturers," for "traceability, energy conservation, [and] responsible management of waste products." Untanned hides can be dried and made pliable by rubbing and stretching
434-480: A lime made from kankar which is a form of calcium carbonate. Selenitic lime, also known as Scotts' cement after Henry Young Darracott Scott , is a cement of grey chalk or similar lime, such as in the Lias Group , with about 5% added gypsum plaster (calcined gypsum ). Selenite is a type of gypsum, but selenitic cement may be made using any form of sulfate or sulfuric acid . Sulfate arrests slaking, causes
496-468: A limitation on its unhydrated oxide content." The term Type S originated in 1946 in ASTM C 207 Hydrated Lime for Masonry Purposes. Type S lime is almost always dolomitic lime, hydrated under heat and pressure in an autoclave, and used in mortar, render , stucco , and plaster . Type S lime is not considered reliable as a pure binder in mortar due to high burning temperatures during production. Kankar lime,
558-400: A skin at a slaughterhouse, farm, or local fur trader. Before tanning, the skins are often dehaired, then have fat, meat and connective tissue removed. They are then washed and soaked in water with various compounds, and prepared to receive a tanning agent. They are then soaked, stretched, dried, and sometimes smoked. Preparing hides begins by curing them with salt to prevent putrefaction of
620-522: A vat of water and let them deteriorate for months. The mixture would then be placed over a fire to boil off the water to produce glue. A tannery may be associated with a grindery, originally a whetstone facility for sharpening knives and other sharp tools, but later could carry shoemakers ' tools and materials for sale. There are several solid and waste water treatment methodologies currently being researched, such as anaerobic digestion of solid wastes and wastewater sludge. Lime (material) Lime
682-471: Is also known as rich, common, air, slaked, slack, pickling, hydrated, and high calcium lime. It consists primarily of calcium hydroxide which is derived by slaking quicklime (calcium oxide), and may contain up to 5% of other ingredients. Pure lime sets very slowly through contact with carbon dioxide in the air and moisture; it is not a hydraulic lime so it will not set under water. Pure lime is pure white and can be used for whitewash, plaster, and mortar. Pure lime
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#1732771875280744-414: Is an inorganic material composed primarily of calcium oxides and hydroxides . It is also the name for calcium oxide which occurs as a product of coal-seam fires and in altered limestone xenoliths in volcanic ejecta. The International Mineralogical Association recognizes lime as a mineral with the chemical formula of CaO. The word lime originates with its earliest use as building mortar and has
806-400: Is called the lime cycle . The conditions and compounds present during each step of the lime cycle have a strong influence of the end product, thus the complex and varied physical nature of lime products. An example is when slaked lime (calcium hydroxide) is mixed into a thick slurry with sand and water to form mortar for building purposes. When the masonry has been laid, the slaked lime in
868-419: Is considered one of the most effective tanning compounds. Chromium-tanned leather can contain between 4 and 5% of chromium. This efficiency is characterized by its increased hydrothermal stability of the skin, and its resistance to shrinkage in heated water. Vegetable tanning uses tannins (a class of polyphenol astringent chemicals), which occur naturally in the bark and leaves of many plants. Tannins bind to
930-403: Is consistent with cross-linking by polychromium species, of the sort arising from olation and oxolation. Before the introduction of the basic chromium species in tanning, several steps are required to produce a tannable hide. The pH must be very acidic when the chromium is introduced to ensure that the chromium complexes are small enough to fit between the fibers and residues of the collagen. Once
992-479: Is done by composition as high calcium, argillaceous (clayey), silicious , conglomerate , magnesian , dolomite , and other limestones . Uncommon sources of lime include coral, sea shells, calcite and ankerite . Limestone is extracted from quarries or mines . Part of the extracted stone, selected according to its chemical composition and optical granulometry , is calcinated at about 900 °C (1,650 °F) in lime kilns to produce quicklime according to
1054-416: Is excellent for use in handbags and garments. After application of the chromium agent, the bath is treated with sodium bicarbonate in the basification process to increase the pH to 3.8–4.0, inducing cross-linking between the chromium and the collagen. The pH increase is normally accompanied by a gradual temperature increase up to 40 °C. Chromium's ability to form such stable bridged bonds explains why it
1116-501: Is made by adding forms of silica or alumina such as clay to the limestone during firing, or by adding a pozzolana to pure lime. Hydraulic limes are classified by their strength: feebly , moderately and eminently hydraulic lime. Feebly hydraulic lime contains 5-10% clay, slakes in minutes, and sets in about three weeks. It is used for less expensive work and in mild climates. Moderately hydraulic lime contains 11-20% clay, slakes in one to two hours, and sets in approximately one week. It
1178-690: Is named for the Dolomite Mountains in the Italian and Austrian Alps. In the United States the most commonly used masonry lime is Type S hydrated lime which is intended to be added to Portland cement to improve plasticity , water retention and other qualities. The S in type S stands for special which distinguishes it from Type N hydrated lime where the N stands for normal. The special attributes of Type S are its "...ability to develop high, early plasticity and higher water retentivity and by
1240-419: Is not very flexible. It is used for luggage, furniture, footwear, belts, and other clothing accessories. Wet white is a term used for leathers produced using alternative tanning methods that produce an off-white colored leather. Like wet blue, wet white is also a semifinished stage. Wet white can be produced using aldehydes , aluminum, zirconium, titanium, or iron salts, or a combination thereof. Concerns with
1302-428: Is preferred. Once bating is complete, the hides and skins are treated by first soaking them in a bath containing common salt (sodium chloride), usually 1 quart of salt to 1 gallon of hot water. When the water cools, one fluid ounce of sulfuric acid is added. Small skins are left in this liquor for 2 days, while larger skins between 1 week and as much as 2 months. In vegetable tanning, the hides are made to soak in
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#17327718752801364-425: Is similar to hydraulic lime but has less soluble silica (usually minimum 6%) and aluminates , and will set under water but will never harden. Hydraulic lime is also called water lime . Hydraulic lime contains lime with silica or alumina and sets with exposure to water and can set under water. Natural hydraulic lime (NHL) is made from a limestone which naturally contains some clay . Artificial hydraulic lime
1426-492: Is soluble in water containing carbonic acid , a natural, weak acid which is a solution of carbon dioxide in water and acid rain so it will slowly wash away, but this characteristic also produces autogenous or self-healing process where the dissolved lime can flow into cracks in the material and be redeposited, automatically repairing the crack. Semi-hydraulic lime, also called partially hydraulic and grey lime, sets initially with water and then continues to set with air. This lime
1488-421: Is tawed by soaking in a warm potash alum and salts solution, between 20 and 30 °C (68 and 86 °F). The process increases the hide's pliability, stretchability, softness, and quality. Then, the hide is air dried (crusted) for several weeks, which allows it to stabilize. The use of alum alone for tanning rawhides is not recommended, as it shrinks the surface area of the skin, making it thicker and hard to
1550-420: Is the characteristic of the keratin class of proteins that gives strength to hair and wools (keratin typically makes up 90% of the dry weight of hair). The hydrogen atoms supplied by the sharpening agent weaken the cystine molecular link whereby the covalent disulfide bond links are ultimately ruptured, weakening the keratin. To some extent, sharpening also contributes to unhairing, as it tends to break down
1612-439: Is used as a leather tanning agent, can cause problems in the kidneys and liver and is also considered a carcinogen . Formaldehyde and arsenic, which are used for leather finishing, cause health problems in the eyes, lungs, liver, kidneys, skin, and lymphatic system and are also considered carcinogens. The waste from leather tanneries is detrimental to the environment and the people who live in it. The use of old technologies plays
1674-632: Is used for better quality work and exterior walls in freezing climates. Eminently hydraulic lime contains 21-30% clay, slakes very slowly, and sets in approximately a day. It is used in harsh environments such as damp locations and near saltwater. Hydraulic lime is off-white in color. "The degree of hydraulicity of mortars will affect many characteristics. By selecting an appropriate ratio of clay to limestone mortars that carbonate or set hydraulically to varying extents can be designed for particular application requirements such as setting time, strength, colour, durability, frost resistance, workability, speed of set in
1736-461: Is used in leather crafting and in making small leather items, such as wallets, handbags and clothes. Chromium(III) sulfate ( [Cr(H 2 O) 6 ] 2 (SO 4 ) 3 ) has long been regarded as the most efficient and effective tanning agent. Chromium(III) compounds of the sort used in tanning are significantly less toxic than hexavalent chromium , although the latter arises in inadequate waste treatment. Chromium(III) sulfate dissolves to give
1798-407: Is usually crushed limestone, not a product of a lime kiln. Otherwise it most commonly means slaked lime , as the more dangerous form is usually described more specifically as quicklime or burnt lime . In the lime industry, limestone is a general term for rocks that contain 80% or more of calcium or magnesium carbonate , including marble , chalk , oolite , and marl . Further classification
1860-411: The adoption in medicine of soaking gut sutures in a chromium (III) solution after 1840, it was discovered that this method could also be used with leather and thus was adopted by tanners. The tanning process begins with obtaining an animal skin. When an animal skin is to be tanned, the animal is killed and skinned before the body heat leaves the tissues. This can be done by the tanner, or by obtaining
1922-408: The bark of certain trees, in the production of leather. An alternative method, developed in the 1800s, is chrome tanning, where chromium salts are used instead of natural tannins. Tanning hide into leather involves a process which permanently alters the protein structure of skin, making it more durable and less susceptible to decomposition and coloring. The place where hides are processed is known as
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1984-491: The case of Bangladesh, chickens (the nation's most common source of protein). Up to 25% of the chickens in Bangladesh contained harmful levels of hexavalent chromium, adding to the national health problem load. Chromium is not solely responsible for these diseases. Methylisothiazolinone , which is used for microbiological protection (fungal or bacterial growth), causes problems with the eyes and skin. Anthracene , which
2046-436: The collagen from bacterial growth during the time lag from procuring the hide to when it is processed. Curing removes water from the hides and skins using a difference in osmotic pressure. The moisture content of hides and skins is greatly reduced, and osmotic pressure increased, to the point that bacteria are unable to grow. In wet-salting, the hides are heavily salted, then pressed into packs for about 30 days. In brine -curing,
2108-459: The collagen proteins in the hide and coat them, causing them to become less water-soluble and more resistant to bacterial attack. The process also causes the hide to become more flexible. The primary barks processed in bark mills and used in modern times are chestnut , oak , redoul , tanoak , hemlock , quebracho , mangrove , wattle (acacia; see catechol ), and myrobalans from Terminalia spp., such as Terminalia chebula . In Ethiopia ,
2170-416: The collagen's carboxyl groups, amine groups from the side chains of the amino acids , and masking agents. Masking agents are carboxylic acids , such as acetic acid , used to suppress formation of polychromium(III) chains. Masking agents allow the tanner to further increase the pH to increase collagen's reactivity without inhibiting the penetration of the chromium(III) complexes. Collagen is characterized by
2232-544: The combined vegetable oils of Niger seed ( Guizotia abyssinica ) and flaxseeds were used in treating the flesh side of the leather, as a means of tawing, rather than of tanning. In Yemen and Egypt , hides were tanned by soaking them in a bath containing the crushed leaves and bark of the Salam acacia (Acacia etbaica; A. nilotica kraussiana). Hides that have been stretched on frames are immersed for several weeks in vats of increasing concentrations of tannin. Vegetable-tanned hide
2294-409: The desired level of penetration of chrome into the substance is achieved, the pH of the material is raised again to facilitate the process. This step is known as basification. In the raw state, chrome-tanned skins are greyish-blue, so are referred to as wet blue . Chrome tanning is faster than vegetable tanning (taking less than a day for this part of the process) and produces a stretchable leather which
2356-425: The end use of the leather, hides may be treated with enzymes to soften them, a process called bating . In modern tanning, these enzymes are purified agents, and the process no longer requires bacterial fermentation (as from dung-water soaking) to produce them. Pickling is another term for tanning, or what is the modern equivalent of turning rawhide into leather by the use of modern chemical agents, if mineral tanning
2418-562: The fibers with a hide stretcher, and fatting. However the hide will revert to rawhide if not periodically replenished with fat or oil, especially if it gets wet. Many Native Americans of the arid western regions wore clothing made by this process. Smoke tanning is listed among the conventional methods like chrome tanning and vegetable tanning. Impregnation of the hide's cells with formaldehyde (from smoke) offers some microbial and water resistance. Leftover leather would historically be turned into glue . Tanners would place scraps of hides in
2480-633: The formation of magnesium sulfate salts." Magnesium sulfate salts may damage the mortar when they dry and recrystallize due to expansion of the crystals as they form, which is known as sulfate attack . Lime used in building materials is broadly classified as "pure", "hydraulic", and "poor" lime; can be natural or artificial ; and may be further identified by its magnesium content such as dolomitic or magnesium lime. Uses include lime mortar , lime plaster , lime render , lime-ash floors , tabby concrete , whitewash , silicate mineral paint , and limestone blocks which may be of many types . The qualities of
2542-418: The hair proteins. The isoelectric point of the collagen (a tissue-strengthening protein unrelated to keratin) in the hide is also shifted to around pH 4.7 due to liming. Any hairs remaining after liming are removed mechanically by scraping the skin with a dull knife, a process known as scudding. The pH of the collagen is then reduced so the enzymes may act on it in a process known as deliming. Depending on
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2604-406: The hexaaquachromium(III) cation, [Cr(H 2 O) 6 ] , which at higher pH undergoes processes called olation to give polychromium(III) compounds that are active in tanning, being the cross-linking of the collagen subunits. The chemistry of [Cr(H 2 O) 6 ] is more complex in the tanning bath rather than in water due to the presence of a variety of ligands. Some ligands include the sulfate anion,
2666-459: The hides are agitated in a saltwater bath for about 16 hours. Curing can also be accomplished by preserving the hides and skins at very low temperatures. The steps in the production of leather between curing and tanning are collectively referred to as beamhouse operations. They include, in order, soaking, liming , removal of extraneous tissues (unhairing, scudding and fleshing), deliming , bating or puering, drenching, and pickling. In soaking,
2728-406: The hides are soaked in clean water to remove the salt left over from curing and increase the moisture so that the hide or skin can be further treated. To prevent damage of the skin by bacterial growth during the soaking period, biocides , typically dithiocarbamates , may be used. Fungicides such as TCMTB may also be added later in the process, to protect wet leathers from mold growth. After 1980,
2790-502: The link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Tanyard&oldid=905953322 " Categories : Disambiguation pages Place name disambiguation pages Hidden categories: Short description is different from Wikidata All article disambiguation pages All disambiguation pages Tanning (leather) Historically, vegetable based tanning used tannin , an acidic chemical compound derived from
2852-437: The magnesium compounds also slake to periclase which slake more slowly than calcium oxide and when hydrated produce several other compounds. Thus, these limes contain inclusions of portlandite , brucite , magnesite , and other magnesium hydroxycarbonate compounds. These magnesium compounds have very limited, contradictory research which questions whether they "...may be significantly reactive with acid rain, which could lead to
2914-752: The many types of processed lime affect how they are used. The Romans used two types of lime mortar to make Roman concrete , which allowed them to revolutionize architecture, sometimes called the Concrete revolution . Lime has many complex qualities as a building product including workability which includes cohesion, adhesion, air content, water content, crystal shape, board-life, spreadability, and flowability; bond strength; comprehensive strength; setting time; sand-carrying capacity; hydraulicity; free lime content; vapor permeability; flexibility; and resistance to sulfates. These qualities are affected by many factors during each step of manufacturing and installation, including
2976-420: The mortar slowly begins to react with carbon dioxide to form calcium carbonate (limestone) according to the reaction: The carbon dioxide that takes part in this reaction is principally available in the air or dissolved in rainwater so pure lime mortar will not recarbonate under water or inside a thick masonry wall. The lime cycle for dolomitic and magnesium lime is not well understood but more complex because
3038-476: The original ingredients of the source of lime; added ingredients before and during firing including inclusion of compounds from the fuel exhaust; firing temperature and duration; method of slaking including a hot mix (quicklime added to sand and water to make mortar), dry slaking and wet slaking; ratio of the mixture with aggregates and water; the sizes and types of aggregate; contaminants in the mixing water; workmanship; and rate of drying during curing. Pure lime
3100-427: The outskirts of town, among the poor. Tanning by ancient methods is so foul-smelling that tanneries are still isolated from those towns today where the old methods are used. Skins typically arrived at the tannery dried stiff and dirty with soil and gore. First, the ancient tanners would soak the skins in water to clean and soften them. Then they would pound and scour the skin to remove any remaining flesh and fat . Hair
3162-405: The presence of water, vapour permeability etc." Poor lime is also known as lean or meager lime. Poor lime sets and cures very slowly and has weak bonding. Poor lime is grey in color. Magnesium lime contains more than 5% magnesium oxide (BS 6100) or 5-35% magnesium carbonate (ASTM C 59-91). Dolomitic lime has a high magnesium content of 35-46% magnesium carbonate (ASTM C 59-91). Dolomitic lime
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#17327718752803224-508: The process. Chemicals used in tanned leather production increase the levels of chemical oxygen demand and total dissolved solids in water when not disposed of responsibly. These processes also use large quantities of water and produce large amounts of pollutants. Boiling and sun drying can oxidize and convert the various chromium(III) compounds used in tanning into carcinogenic hexavalent chromium , or chromium(VI). This hexavalent chromium runoff and scraps are then consumed by animals, in
3286-444: The quicklime to a form referred to as lime putty. Because lime has an adhesive property with bricks and stones, it is often used as a binding mortar in masonry works. It is also used in whitewashing as a wall-coat to allow the whitewash to adhere the wall. The process by which limestone (calcium carbonate) is converted to quicklime by heating, then to slaked lime by hydration, and naturally reverts to calcium carbonate by carbonation
3348-409: The reaction: Before use, quicklime is hydrated , that is combined with water, called slaking, so hydrated lime is also known as slaked lime, and is produced according to the reaction: Dry slaking is slaking quicklime with just enough water to hydrate the quicklime, but to keep it as a powder; it is referred to as hydrated lime. In wet slaking , a slight excess of water is added to hydrate
3410-838: The sense of sticking or adhering . These materials are still used in large quantities as building and engineering materials (including limestone products, cement , concrete , and mortar ), as chemical feedstocks, for sugar refining , and other uses. Lime industries and the use of many of the resulting products date from prehistoric times in both the Old World and the New World. Lime is used extensively for wastewater treatment with ferrous sulfate . The rocks and minerals from which these materials are derived, typically limestone or chalk , are composed primarily of calcium carbonate . They may be cut, crushed, or pulverized and chemically altered. Burning ( calcination ) of calcium carbonate in
3472-403: The tanning agent (chromium salts). Later during pickling, collagen carboxyl groups are temporarily protonated for ready transport of chromium ions. During basification step of tanning, the carboxyl groups are ionized and coordinate as ligands to the chromium(III) centers of the oxo-hydroxide clusters. Tanning increases the spacing between protein chains in collagen from 10 to 17 Å. The difference
3534-407: The touch. If alum is applied to the fur, it makes the fur dull and harsh. Depending on the finish desired, the leather may be waxed, rolled, lubricated, injected with oil, split, shaved, or dyed. The tanning process involves chemical and organic compounds that can have a detrimental effect on the environment. Agents such as chromium, vegetable tannins, and aldehydes are used in the tanning step of
3596-492: The toxicity and environmental impact of any chromium (VI) that may form during the tanning process have led to increased research into more efficient wet white methods. The conditions present in bogs, including highly acidic water, low temperature, and a lack of oxygen, combine to preserve but severely tan the skin of bog bodies . Tawing is a method that uses alum and other aluminium salts , generally in conjunction with binders such as egg yolk, flour, or other salts. The hide
3658-418: The use of pentachlorophenol and mercury -based biocides and their derivatives was forbidden. After soaking, the hides are treated with milk of lime (a basic agent) typically supplemented by "sharpening agents" (disulfide reducing agents) such as sodium sulfide , cyanides , amines , etc. This: The weakening of hair is dependent on the breakdown of the disulfide link of the amino acid cystine , which
3720-419: Was a fermentative process that relied on enzymes produced by bacteria found in the dung. Among the kinds of dung commonly used were those of dogs or pigeons. Historically the actual tanning process used vegetable tanning. In some variations of the process, cedar oil , alum , or tannin was applied to the skin as a tanning agent. As the skin was stretched, it would lose moisture and absorb the agent. Following
3782-533: Was being carried out by the inhabitants of Mehrgarh in Pakistan between 7000 and 3300 BCE. Around 2500 BCE , the Sumerians began using leather, affixed by copper studs , on chariot wheels . The process of tanning was also used for boats and fishing vessels: ropes, nets, and sails were tanned using tree bark. Formerly, tanning was considered a noxious or "odoriferous trade" and relegated to
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#17327718752803844-424: Was removed by soaking the skin in urine , painting it with an alkaline lime mixture, or simply allowing the skin to putrefy for several months then dipping it in a salt solution. After the hair was loosened, the tanners scraped it off with a knife. Once the hair was removed, the tanners would " bate " (soften) the material by pounding dung into the skin, or soaking the skin in a solution of animal brains. Bating
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