Leather Industry Glossary Terms
The underlying layer of a hide or skin, known as the “flesh”. In the preparation of the skin for tanning, the adipose tissue is thoroughly removed by the fleshing operation in the beamhouse.
Air-dried hides or skins
Hides cured by exposure of the flesh side to mild rays of the sun until they are dry: usually the hides are tensioned by lacing into a square wooden frame.
Leather that has been through-dyed and then finished with transparent finishing chemicals so as to retain the natural beauty of the leather. No opaque finishing chemicals are used in the finishing formulation.
The main portion of a raw hide, obtained by first cutting the hide longitudinally along the backbone, then trimming off head and belly, leaving a “bend” and shoulder.
Deteriorative effects on hides, skins or leather caused by bacteria.
A special hydrometer used in tanneries to test the strength of tanning liquids by specific density.
Usually the first finish coat that is applied to the leather surface.
The chemical binding of the tanning chemicals to the skin protein. This is achieved by raising the pH slowly in the tanning liquor.
The softening of skins by treating them with pancreatic enzymes. The enzymes remove unwanted skin components (unwanted nitrogenous constituents) making the final leather soft.
A convex wooden slab sloping downwards from about waist height, over which a hide or skin is placed for trimming off excess flesh or for unhairing by hand.
The area of a tannery where non-leather forming substances are removed from the skin prior to tanning. The beamhouse operations include soaking, fleshing, liming, unhairing, deliming and bating. The name “beamhouse” was originally applied to the building where skilled artisans fleshed hides and scraped away all hair and epidermis prior to tanning. The hide was spread over a broad oval wooden beam, and hence the name.
The underside of a hide between the fore and the hind legs.
The portion of a cattle hide remaining after the hide has been cut in half and the shoulder and belly portions have been trimmed off. The bend is usually the best part of the hide and is used for making soles of boots and shoes, saddles etc. The term bend is only used inrefeering to tanned leather. For untanned hides, the term croupon is used.
A test applied to chrome-tanned leather during the tannage to ascertain whether or not it is fully tanned. A 10cm x 10cm piece of wet blue is placed in boiling water for 2 – 3 minutes. If the wet blue curls or shrinks, it is considered not fully tanned or properly basified.
Animal of the ox or cow family
Marking or printing with a hot iron, freeze process, or punch. Cattle are branded with markings that identify ownership but also damages the hide.
The break of leather refers to the pattern of parallel folds or tiny wrinkles formed on the grain side when it is bent inwards. Leather buyers often flex shoe upper leather in order to get an indication of the way in which the appearance of the leather will be preserved in a shoe during wear.
A saturated solution of common salt and water used for preserving raw stock to be later used for making leather.
Leather from which the top surface of the grain has been removed by an abrasive cylinder of sandpaper.
A solution of a weak acid or alkali and the corresponding salt used to minimize changes in pH values.
The part of the hide left after the bellies and shoulders have been removed.
Leather made from the skins of young cattle from a few days to a few weeks old. It is soft, fine-grained and supple and possesses considerable strength in relation to its weight and substance. It is lighter weight than cowhide leathers and more supple; also lighter and finer grained than side, kip or split leathers, which are used in place of calf leather for many purposes. Calf leather may be either chrome or vegetable tanned, chrome leather being the most common.
A protein substance prepared by precipitation of skim milk. Large quantities of casein are used by the tanning industry in making leather finishes. It is never applied alone, but always mixed with solutions of other materials such as shellac or Irish moss or with emulsions of wax, etc.
The skin of a fully grown bovine animal.
A soft pliable absorbent oil tanned leather which is recognized in this country and abroad as being made from sheepskin, from which the outer or grain side has been split prior to tanning, known technically as a flesher.
A blue colored leather that has been chrome tanned. It does not wet black readily and is heat stable in boiling water. It is stronger than vegetable-tanned leather and is usually dyed and finished.
Solution of basic chrome salt, usually basic chromium sulphate, used in chrome tanning.
Leather which has been first chrome tanned throughout its thickness and subsequently further treated or tanned with vegetable or synthetic tanning agents, or resin filling materials; these may be partially or fully penetrated.
Chrome tanning extract
Green crystals of chrome salt, prepared by the reduction of sodium dichromat and sulfuric acid with a reducing agent; supplied for tanning pelts by the one-bath chrome-tanning process.
The main skin protein that is tanned and which becomes leather. Most other skin components are removed during the beamhouse processes.
A process of tanning leather by a combination of tanning agents. This combination may consist of several vegetable-tanning materials, or of vegetable – and mineral-tanning agents.
The addition of a small amount of moisture into the crust leather for lubrication and to render them supple prior to some of the harsh softening processes that follow (staking, milling). Conditioning may be done by cooling, sawdusting, or by damping with water in pile.
The second layer of a hide or skin, containing the fiber mass that is the real leather-making part of the skin. The corium also known as the derma, or true skin, is made up of fibers, which are long strands of fine threadlike units, or fibrils (little fibers). The fibers are arranged into little groups, or fiber bundles and theses bundles are the architectural units of the skin.
Term used to describe leathers which have been buffed to remove grain blemishes and scars before final finishing. The grain correction improves the appearance of the leather without necessarily detracting from its strength and quality.
Hides from country areas removed by relatively unskilled labor, e.g. by country butchers or smaller packing plants where they are more likely to be damaged and/or less uniform in shape and therefore command lower prices than big-packer hides.
Chemicals which are used to toughen the finish film and which are also used to improve the water resistance of polyurethane resins and lacquers.
Leather that has been through the dyehouse processes and has been dried, but not yet finished.
The treatment of raw hides and skins after flaying to retard bacterial action and putrefaction. When thoroughly cured by any one of several common methods, the hides and skins are stored until they are taken by the tanner, whose first operations are to soak the hides and skins for softening and submit them to further preparatory treatment before they can be tanned into leathers.
Removal of salt and excess grease from pigskins, sheepskins, etc by drumming stock in a liquor containing kerosene and slat, gasoline, or similar hydrocarbons, before tanning. Patent leather is frequently degreased by drumming the dry leather in naphtha after tanning and before applying the finishing coats. The residual grease recovered through degreasing operation is often refined and used as a tanning oil.
The removal of lime from the skin usually achieved by ammonium sulphate or ammonium chloride. The skin swelling is reduced as the pH is reduced. After the deliming process, the hides and skins are then in a condition for bating.
The process of loosening the hair on hides and skins to permit its removal without damage to the stock.
Surface-active compounds or formulation added to the water that serve to cleanse skin, such as soap for instance.
The wrinkling of the grain layer due to uneven swelling or excess mechanical action during the liming process. The main leather substance has contracted relative to the grain layer leaving a puckered grain effect which may appear as parallel ridges if the contractions occur in one direction only, or may appear as an overall pebbled effect if the contractions form uniformly in all directions.
The most commonly employed method of applying dyestuffs to leathers. In drum dyeing, the leather stock is placed in a drum, neutralized and then washed with warm water to remove soluble salts. The coloring matter is added to the revolving drum, and the dyeing procedure is generally carried out at 60°C for 1 to 3 hours.
Hides which have been salted in the same manner as green salted hides, i.e. by covering them with salt on the flesh side and piling (see Curing), but are later spread out and allowed to dry in the shade or sun. It is used as a curing method instead of flint drying because the hides do not shrink during drying and are much more readily softened in soaking prior to tanning.
One of the simplest forms of curing hides and skins; now chiefly use for goatskins coming from areas where other forms of cure would be difficult, or where salt is not available. The skins are dried spread out in the sunshine or in the shade with good ventilation and are called flint-dried when completely cured because of their hardness.
A dye (or dyestuff) is usually an organic compound used to impart color to a substance. It may be used for the coloring of animal, vegetable, or synthetic fibers (e.g. wool, leather, fur or cotton). Insoluble coloring matters are called “pigments”. Dyes may be classified in accordance with their chemical characteristics.
The dyeing of the wet blue or wet white to the color required by the customer.
A process similar to plating but instead of a smooth plate being used, an engraved plate is used, which presses a pattern into the leather surface. This is produced by pressure upon the grain surface of leather. The pattern may be transferred from a plate or roller according to the type of embossing machine. The engraved embossing plate or roller is heated which assists in transferring the pattern to the leather surface.
Combining two liquids that are not mutually soluble, such as oil and water, into a homogeneous emulsion.
A soluble, colloidal protein catalyst produced by a living organism. Trypsin, the most important enzyme in lather manufacturing, comes chiefly from cattle pancreas and certain mold. Trypsin is the active ingredient of tryptic bates which are enzyme bating material and of the enzyme dehairing formulations.
The protective film of keratin cells over the dermis. It is composed of an outermost layer of dead cells mainly and a transitional layer that contains newly formed cells. These layers are removed in the process of liming or unhairing (depilation).
Hides taken from cattle that have died naturally as distinct from those which have been slaughtered. There is a large proportion of fallen hides among Indian hides.
An emulsion of oils and grease with soap or sulphated oils in which hides and skins are worked after tanning to lubricate the fibers, add flexibility to the leather and increase strength. A wide variety of oils, greases and emulsifying agents are used for this purpose and fatliquoring processes vary accordingly. The purpose is the same in each case, to lubricate the fibers and improve the leather flexibility.
The addition of oils or fatliquors to the leather to make the leather soft. The more fatliquor that is added, the softer the leather becomes.
The use of formic acid to lower the pH of the leather resulting in the binding of the dyehouse chemicals to the leather.
Process of removal of the hide or skin from the animal carcass.
Flesh surface of the hide as opposed to the hair-bearing or grain side.
Small bacterially-caused spots or depressions on the flesh surface of leather. They often dye lighter in color in contrast with the surrounding unaffected areas of the flesh surface.
Removal of the fatty layer usually by fleshing machine that helps with the penetration of chemicals into the skin in subsequent process stages. Can be done when the hide is in the green state or fater the liming process.
The pocket or tubular cavity in the skin surface from which the hair or wool grows.
Full chrome (tanned)
The qualification “full” is used with “chrome tanned” to denote that the leather has not been tanned by the semi-chrome or combination chrome processes.
First split taken from the hair or grain side of the hide after removal of the hair and associated epidermis suitable for footwear or upholstery purposes. Scars, scratches or other imperfections may be lightly buffed or corrected but the total area so affected should not exceed 5% of the total surface of the hide. Generally, full grain leather has undergone no buffing, snuffing or splitting.
The operation of producing a bright, glossy or glass-like finish on the grain surface of leather by subjecting it to the action of a machine that rapidly draws, under pressure, a tool of glass across the suitable prepared surface of the leather.
Leather which has the grain layer substantially intact and is finished on the grain side.
Indicates the outer or hairside of a hide or skin.
Superficial pitted effect affecting the grain enamel of the leather caused by the start of bacterial action on the skin.
Quality of the grain surface, its smoothness, fineness and freedom from flaws such as scratches, wrinkles, growth marks. This is one of the most important considerations in appraising the value of leather.
Similar to pin-prick damage, but affecting larger areas where patches of grain enamel are removed due to bacterial action.
Extensive grain enamel loss due to bacterial action that affects a considerable area of the grain surface.
Sun drying of hides and skins for which they are stretched on the ground, flesh side uppermost and either weighted down with stone or pegged to the ground through holes around the edges; frame drying is preferable, however.
A slender threadlike outgrowth of the skin, made of dead keratin cells cemented together. They grow out of tubular cavities in the dermis, the hair follicles. Hair is composed of a cuticle on the outside and a cortex with a central cavity, the medulla. The color of the hair often determines its value. For example, black cow hair is less valuable than white cow hair. Hair taken from skins and hides in depilation is used extensively in the stuffing of furniture, making carpets, plastering, and various other industrial and commercial applications.
A projection from the dermis into the hair root bulb through which nutrients are supplied to the growing hair.
Type of sheep bearing coarse hair instead of fine wool. The resulting leather has a finer and firmer grain than that of a wool sheep.
Slipping or loosening of the hair in hides or skins due to putrefaction. If the slip is not very bad, acceptable leather can be made; if too far advanced, the hide is damaged and can only be made into glue, Slippy hides are, therefore, often called “glue stock”.
Chemicals such as waxes or silicones that are used to change the feel of the surface of the leather.
A female bovine less than 3 years of age that has not produced a calf.
The skin covering from a large animal such as a cow or ox or bull.
Piling of wet blue or leather on a wooden stand known as “horse”. Also carried out on pallets. Allows excess water to drain off and also gives time for chemical reactions with the hide or skin to occur.
Cattle hide leather including flexible splits, vegetable or combination tanned, in sides, bends, shoulders and bellies suitable for the inner soles of footwear.
Chemicals that are used in the top coats of finishes and which give the properties that the top coat must have.
The application of a protective film onto the leather surface to make it more durable and to try and hide as many defects on the leather surface as possible.
White patches or spots on limed skin caused by calcium carbonate deposits, leading to rough grain.
Saturated solution of lime having excess of undissolved lime that forms a milky liquor on stirring; used in unhairing hides and skins prior to tanning.
Depilatory solution mixed with slaked lime or china clay to form a thin paint, which is applied to the flesh side of sheep, goat or calfskin.
The swelling of the skin using lime. The swelling is important for the proper opening up of the fiber structure that is important in the making of leather.
The number of square feet in a skin of light leather is determined by measuring the area of leather on one of several types of measuring machine. The leather is measured at the tannery and each skin is marked with the square area it contains (in units of square decimeters or feet). Many manufacturers also have measuring machines and check tanners’ measurements against their own, as inaccuracies may be found in the original measurements because of shrinkage of the skin in transit.
The tumbling of crust leather in wooden or stainless steel drums to soften it.
A microscopic growth or discoloration produced on leather surfaces (and on other organic substances), especially when damp. Mold on leather is frequently confused by the layman with bloom and spew, which are also discolorations, but are caused by entirely different conditions and have different effects on leather quality.
Chrome, alum or combination tanned sheepskin glove leather, drum colored.
The removal of acidity from the wet blue or wet white which allows the dyehouse chemicals to penetrate through the cross-section of the wet blue or wet white.
Hide leather, buffed on the grain side to give a velvet surface.
Leather with a glossy impermeable finish produced by successive coats of drying oils, varnish or synthetic resins.
A measure of the relative acidity and alkalinity of a solution; solutions having a pH value of 7.0 are neutral; (neither acidic or alkaline); pH-values 1 to 6 denote acidity; pH values of 8 to 14 denote alkalinity.
A hide or skin, usually in the raw state with the hair or wool left on. Most frequently used to designate the skins of fur bearing animals.
The lowering of the pH of the skins using sulfuric acid or formic acid preparing the skin for the tanning chemicals. The tanning chemicals penetrate easily into the skin at low pH. Is also a method of preserving stock with brine for storage or shipment. It is used chiefly for sheep, lamb and goatskins that are frequently placed in brine in barrels and shipped in this way.
Denotes leather surface coating with a material containing pigment or other opaque material.
Colored chemicals that give the color to the leather finish but which also help to hide defects on the leather.
Characteristic of loose grain leather, which forms coarse wrinkles on bending with the grain inward.
A process whereby leather is put in a press under high temperature and pressure. Plating makes the leather finish very smooth and helps it stick to the leather surface.
An additive used to prevent decay or decomposition. The traditional preservative used in the making of leather is common salt, which is also important at several stages of the process of converting hides into leather. It is used in excess to saturate and preserve hides before they are taken through the leather making stages.
Complex organic substances present in all living cells, both animal and plant. They all contain nitrogen, carbon, hydrogen and oxygen and frequently some sulphur. With the exception of small quantities of inorganic matter, fats and pigment, the chemical constituents of hides and skins are proteins. Leather is formed by the interaction of vegetable tanning or mineral tanning salts with the hide protein.
The hides and skins in the untanned state used for making leather.
The usual American name for cattle hide that has been dehaired and limed, often stuffed with oil or grease and sometimes undergone other preparatory processes; usually has not been tanned. Some rawhide is tanned with the hair left on. Used principally for mechanical applications such as belt facings and pins, loom pickers, gaskets, pinions, gears and also for trunk bindings and luggage.
The process whereby chrome is added to the wet blue or wet white. Usually used to level out chrome differences from batch to batch or used when making very soft leather.
Chemicals such as acrylics, butadienes and polyurethanes, which bind the pigments to the leather surface during the finishing of the leather.
The use of various types of chemicals to give the leather the properties that the final customer wants i.e. softness, fullness, etc.
The removal of water from hides or skins after they have been tanned.
Hides which have been damaged by scratches accumulated during the life of the animal. These are caused by contact with barbed wire fences, nails, thorns and other sharp objects. Such hides are often deeply scratched resulting in infection. They lower the quality of the hide or skin and leather.
Small amounts of hair left behind on the surface of the hide or skin after the liming and unhairing process.
Leather that has been aniline dyed or stained, incorporating a small quantity of pigment, not so much as to conceal the natural characteristics of the hide.
A tannery operation employed to reduce the water content of light leathers before they are split or shaved.
A material added to a lime liquor to accelerate the loosening of the hair of hides and skins immersed in it.
The weight of a pack of skins after shaving in which conditions they retain about 50 percents water content.
The accurate reduction of the thickness of the skin. Usually done at the wet blue or wet white stage.
The temperature at which measurable shrinkage occurs when leather is gradually heated in air or in a fluid. Wet shrinkage is also called hydrothermal.
A hide that has been cut down the backbone into two sides.
The skin covering from a small animal such as a sheep or goat or ostrich
Usually the first process in the tannery where any water lost during the preservation process is re-introduced into the skin making is soft and flexible.
Snuffed top grain
Portions of the grain surface lightly abraded with emery wheel or sandpaper, so as to lessen the effect of grain damage.
Any constituents of leather that come to the surface in the form of a white crystallized deposit or dark gummy deposit.
If a hide or skin is split over its whole area into one or more layers, this process is termed “splitting”. The layers are termed: grain split (outer split); flesh split (inner split); in heavy hides there can also be a middle split. Leather made from the flesh split or middle split is called suede leather.
The cutting of hides into two or more layers and thus reducing the thickness of the original skin. Usually done after the liming process or when the skin has been processed into wet blue.
A machine equipped with a gripping cylinder and band knife for splitting hides or skins or leather horizontally into splits or for leveling leather to a consistent thickness.
A vigorous softening process where the leather is stretched and pummeled by machine, which separates the leather fibers that have become stuck together after the drying process.
The hides or skins used by the leather manufacturers. The term “raw stock” is commonly applied to the hides and skins while they are being tanned and before they have been converted into leather.
A finish produce by abrading the surface of leather on a carborundum or emery wheel to separate the fibers and in order to give the leather a nap. The grain side of the leather may be suede finished in this matter, but the process is most often applied to the flesh side.
Sueded grain enamel
Superficial disruption of the grain enamel surface of the leather resulting in general areas of fine nap or suede affecting grain permeability in finish applications; results in dulling or loss of luster in finish application
The oldest known method of unhairing skins by bacterial action before tanning.
A general term covering the group of synthetic tanning materials used in combination with vegetable, mineral or formaldehyde tannage. These materials are also often used for specialized purposes such as bleaching, filling or mordants.
The addition of tanning chemicals to the skin. Once tanned, the hide or skin will not rot.
A tannery operation whereby skins of light leather are stretched smoothly over perforated metal frames, attached by means of toggles (metal clamps). These fasten to the leather and, in turn carry hooks that can be inserted into holes along the edge of the perforated frame.
Usually the final finish coat that is applied to the leather and which must give the scuff resistance and final feel of the finish.
The removal of the hair from the skin. This is usually achieved using sodium sulfide or sodium hydrosulfide.
A leather used for the upper portions of the shoe. Predominantly from cattle hide and calfskins, although a variety of skins are used. Usually combination tanned.
A tannery operation whereby hides and skins are washed in clear water after having been soaked to remove curing agents, dirt, blood and manure.
Hides or skins that have been properly tanned using chromium sulphate as the tanning agent. Wet blue is an internationally traded commodity as it is stable as does not putrify.
A chemical or solution that will reduce the surface tension and allow easier penetration of the water or solution into the material.
Re-introduction of water into wet blue or wet white. Usually the first process in the dyehouse.
Hides or skins that have been tanned using aldehydes as the tanning agent
Courtesy of the International School of Tanning Technology