Damp leather

Leather with approximately 50% to 60% moisture content.

Damp stuffing

Introduction of more or less liquid grease into damp leather by hand and/or drumming.

Damping plant

See: Conditioning plant.

Daphnia

Micro shellfish used to determine the toxicity of water.

Dappling

Patchy appearance to surface pigment finish due to uneven penetration in certain areas of the grain. Often caused by damaged enamel.

Deacidify

Removal of acid or a process of reducing acidity.

Deamidation

Removal from a molecule of the amido group by splitting it into a free carboxyl group and ammonia (as glutamyl and asparagyl groups in the collagen during liming).

Decantation

Draining off the supernatant liquor after settling of suspended solids.

Decarboxylase

Enzyme capable of removing the carboxyl group from a carboxylic acid or an amino acid.

Dechroming

Treatment of the floats containing chromium (pretanning floats, tanning floats) consisting of a precipitation with different type of coagulants including sodium hydroxide, sodium carbonate, magnesium oxide and lime. A flocculation with polyelectrolyte may follow.

Chromium sludge is then settled and treated in a filter press or vacuum filter. The chromium cake might be reused for tanning or landfilled.

Decolourise (v); decolourising

Deprive, bleach or remove the colour from a material, by chemical treatment or sunlight and weather effect.

Dedust (v); dedusting

Remove dust from the surface of leather which is produced when leather is buffed. See: Air blast; brush (v); brushing

Defoamer

Finishing auxiliary used to avoid foaming of finish preparations. Especially used in finishing applications like curtain coating and roller coating.

Deformability

Ability to allow a permanent change in shape, when subjected to stress, without  suffering damage, as in shoe lasting.

Degrain

Remove the grain of a leather by mechanical processes such as splitting, shaving or buffing.

Degras

A pasty, water-in-oil emulsion of unchanged fish oil

(usually cod oil) and oxidation, and other products obtained by washing crude oil-tanned skins with soda solution and acidifying the wash liquor.

Degrease (v); degreasing

To remove grease by any method.

Degree of brightness

Proportion of the luminous intensity of the incident white light, which is reflected and scattered by coloured material, in any surface in a given direction, per unit of projected area for the surface as viewed in that direction.

Degree of dispersion

Proportion of the material particle sizes in a colloidal solution, which exist in the form of smaller, rather than larger.

Degree of dullness

Proportion of the incident white light which is absorbed by a coloured material.

Degree of penetration

Depth to which chemicals such as dyestuff, fat, resin, etc. penetrate into the leather.

Degree of plumping

Extent to which a hide or skin has been rendered resistant to compression through entry of water into its fibres under osmotic forces.

Note: When placed in an acid or alkaline solution.

Degree of saturation

Percentage of the incident light of any wave length which is reflected, emitted, and/or scattered by a coloured material.

Degree of sulphation

Proportion to which –O-SO₃H groups are introduced into the fatty matter by a chemical reaction (sulphation) of an animal or vegetable oil. Measured by the content of organically combined SO₃ .

Degree of swelling

Measure of the degree to which a protein is swollen by the uptake of water, expressed, for example, as percentage increase in weight.

Dehydration

Removal of water.

Delamination

Separation of the grain and corium layers. Can be caused by putrefaction, excessive swelling or any physical degradation of this junction of the two layers.

Note: Staking causing pipiness.

Delayed salting

Salting which has been delayed for so long a period after flaying that damage may have been caused through putrefaction, etc.

Delime (v); deliming

Removal of lime from, or the reduction of pH of, hides and skins by washing or treatment with acid or acidic salts.

Deliming power

Ability of an agent to neutralise the lime of pelts introduced into it.

Demanure (v); demanuring

To free hides from manure (the excrement of an animal) or dung, some fleshing machines have a demanuring cylinder for mechanical demanuring before pre-fleshing. However, application of strong mechanical forces on manure of flesh flayed, unsoaked  hides will damage the hide structure in the grain; therefore thorough soaking and softening of the ‘manure balls’ before mechanical demanuring is indispensable. Processes for chemical or biotechnological demanuring with the help of nonionic and sulphated anionic detergents or mixtures of enzymes (cellulose, xylanases etc.) have been also developed (dung enzymatic removal). Nevertheless, to this day, many hides coming from ‘modern’ farms using intense farming techniques are a real problem to the tanner, in terms of quality of the finished leather grain surface, processing problems (damage in pre-fleshing) and extra environmental loading.

Demodectic mange

Damage to cattle, calf, goat and hair sheepskins involving loss of hair, numerous pimple-like elevations on the surface and considerable underlying destruction. Due to demodex or follicular mites which enter the skin through the hair follicles and migrate and encyst deeper into the skin.

Denaturation

Modification of the protein’s natural molecular structure produced by heating or treating it with chemicals, thus modifying its original properties.

Denatured protein

Native protein modified especially by heat, shaking, acid, alkali, ultra violet radiation, detergents, etc., leading to an alteration of physical properties such as solubility and specific activity.

Density

The mass of a given volume of the actual leather fibre.

De-olation

Cleavage of  links between two metal ions in a polynuclear complex ion, under the action of acid.

Depickle (v); depickling

Neutralise the acid in pickled pelts (raise the pH towards the isoelectric point of collagen) by treating them with chalk, borax, etc., in a saline bath.

Depilation

Removal of hair or wool from hides or skins by any method.

See: Unhair (v); unhairing

Depilatory

Chemical, or preparation, which destroys hair or wool or loosens its attachment to the skin.

Depth of shade

Degree or intensity of required colour. Achieved by careful control of neutralising, retanning, choice of dyestuff and fixation.

Derma

The protective integument of the living (animal) body organs.

See: Dermis.

Dermatan sulphate (DS)

Extremely acidic (bio-) polymer; side chains with a very high charge density containing both sulphate and carboxyl groups, all fully ionised at physiological pH 7,4.

Dermatan sulphate proteoglycan, attached by electrostatic bonding to the collagen fine fibrils immediately below the epidermis in the grain, is extensively removed from the hide under the alkaline conditions of sulphide unhairing / liming.

The removal of this sheath of high charge density from around each collagen fibril is accompanied by the ‘opening up’ of the fibre structure, a partial decrease in shrinkage temperature of the collagen, removal of the interfibrillary protein, combined with a higher flexibility of the limed tissue fibre network.

These fundamental changes to a large extent determine the behaviour of the pelt during processing, the rheology (plastic flow), softness and ability of leather to bear stress during manufacture and during use (‘stressed-skin function’).

Dermatitis

General term for irritations of the skin which cause the animal to rub or scratch. Can be caused by parasitic infestations (such as mycotic and dermatitis) or chemical sprays.

Dermis

The mesodermic layer of the skin made up of the papillary dermis, or grain layer, and the reticular dermis, or corium layer.

On the living animal: epidermis + dermis + hypodermis = derma.

Desorption

Process of removing a sorbed substance by the reverse of adsorption or absorption.

Deswelling

Reduction of the water content in swollen hides and skins by means of chemicals.

Detan (v); detanning

Removal of more or less of the tanning agent from leather.

Determination of acidity

Determination of the total amount of acids in a solution or a material by titration with alkali.

Dewool (v); dewoolling

Removal of previously loosened wool from woolled sheepskin.

Dewoolling knife

Double-handled, concave, blunt scraper for removing the wool from sweated or painted sheepskins.

Diamond-buffing leather

Stout, vegetable-tanned leather made from the hides of pachedermatous animals (elephants and walruses) used for cutting and polishing diamonds.

Diazo group

Any organic group (–N=N-), pertaining to a very reactive compound in which two nitrogen atoms are joined to a hydrocarbon radical, used in dyestuff manufacture.

Diazotise (v); diazotisation

Convert the amino-groups of an aromatic compound to azo-groups (-N=N-) by treatment with nitrite and acid.

Dichloromethane soluble substances

Substances being extractable by dichloromethane from a leather (mainly fats and oils and also resins and other chemicals used in the finishing process).

Differential Scanning Calorimetry (DSC)

Technique for measurement of, and comparison (differential) of, process heats (reaction, absorption, hydrolysis, etc.) for a specimen and a reference material.

Digestion

Mineralisation of sludge and organic waste by anaerobic fermentation, accompanied by the production of methane gas.

Diluent

Finishing auxiliary such as alcohols or aromatic hydrocarbons used in finishing formulations. Often used as mixture with solvents to adjust the rate of evaporation of solutions and to achieve desired film formation, gloss, adhesion or flow out.

Dilutable

Ability of an agent or a solution to be diluted by other agents or mixtures.

Dip

1. Liquid into which something is dipped for treatment, especially one for killing vermin (ectoparasites) on sheep, horse, etc.; A vat or tank for this purpose.

2. Solution of white arsenic (arsenious oxide) in sodium carbonate, into which dried hides and skins are dipped to protect them against insect attack.

Dip dyeing

Process of dyeing in which the skins, usually paired flesh to flesh, are repeatedly dipped into and removed from the dye liquor, contained in a trough.

Dip dyeing

Dyeing of furskins by dipping in the dye bath.

Dip stuffing

Introduction of grease into thoroughly dried leather by dipping it into a hot, molten, grease mixture for the period necessary to ensure the desired depth of penetration.

Diphenyl-methane dyestuff

Dyestuff based upon (C₆H₅)₂ CH₂. Its origin is diphenylamine, a crystalline aromatic amine obtained by heating aniline hydrochloride with aniline, used as a stabiliser and in the manufacture of dyestuffs.

Direct dyestuff

Anionic dyes substantive to cellulose when applied from an aqueous bath containing an electrolyte; also have extensive use on paper, wool, silk, nylon, and for many miscellaneous purposes such as preparation of heavy-metal salts for use as pigments, indicators, etc. In leather many such dyes give full shades on mineral tanned leather.

Discolour (v); discolouring

Become stained, faded, spoiled, or change colour of a surface.

Disease

Diseases of animals which are characterised by skin conditions that may persist in the finished leather thus lowering its value.

Note: Mange, dermatitis, etc.

Disinfectant

Chemical which, in suitable concentration, will kill micro-organisms.

Disperse dyestuff

Substantially water-insoluble dyes having substantivity for one or more hydrophobic fibres.

Note: Used in furs, mineral-tanned leather, and cellulose acetate and usually applied from fine aqueous dispersion with surfactants.

Dispersing agent

Material which, in solution, has the power to bring a powdered solid into a state of suspension and maintain it in that state.

Dispersion

Heterogeneous mixture of substances in which one phase in the form of particles is dispersed more or less finely in another phase by dispersing agents.

Dissolved organic carbon

Mass concentration of substances remaining after filtration according to clearly defined conditions. Expressed in mg/l or g/m³.

Dissolved oxygen (DO)

Dissolved oxygen is the parameter measuring the quantity of oxygen (O₂) dissolved in water. It is a major parameter for biological treatments.

Dissolved solids

Mass concentration of substances remaining after the filtration of a sample and dry evaporation; it is determined in precisely defined conditions.

DO

See: Dissolved oxygen.

Doeskin

1. Skin of doe (adult female deer) or leather made of it;

2. In the glove trade, a very supple leather, usually white or cream, but sometimes dyed with a fine suede finish, made from lamb or sheepskin flesh splits and tanned by aldehyde-oil, or aldehyde-alum processes.

In Germany, ‘Rehleder’ is made only from deer skins. In Holland, this leather may also be made from calf splits. In Italy, chamois leather (oil-tanned lamb and sheepskin splits) is incorrectly termed deer skin.

3. In the shoe trade, a suede leather made from deer skin. The term is almost synonymous with buckskin. 

4. Commercial term for white leather from sheep or lambskins, tanned with alum and/or aldehyde.

Dollar break

Usually following the dry drumming (milling) process, unattractive islands of uncreased grain are left, roughly the size of an American dollar piece. Can be caused by too compact grain, uneven opening of the fibres, uneven fatliquor or constant flexing along lines of weakness such as blood vessels.

Domestic hides

Not wild; kept by or living with humans, tame. 

1. Of or pertaining to one’s own country or nation; not foreign or international; indigenous made in one’s own country, not imported.

2. General term for a raw hide from countries in which animals are kept under domesticated conditions. From European countries and to some extent from North America, Canada and New Zealand; mostly unbranded.

3. In Greece all sheepskins coming from the United Kingdom are called “Domestics”.

Domestic market

The opportunity to buy or sell in one’s own country. Pertaining to one’s own country or nation.

Dongola tannage

Combination tannage with alum, followed by cutch or gambier, or vice-versa.

Double beam spectrophotometer

Instrument that uses a photoelectric circuit to measure the difference in absorption when two closely related wavelengths of light are passed through the same medium.

Double face

A woolled sheepskin, finished on the flesh side (suede or nappalan), used for sheepskin coats, etc.

 See: Shearling; sueded woolled sheepskin.

Double hiding

Separation of the  grain and corium layer. Can be caused by excessive fat cells between the two layers, as in merino sheep. Insufficient pickling can cause a lack of tannage in the centre of the hides which then gelatinise when the heat at the end of the tannage exceeds the shrinkage temperature of the untanned collagen.

Double-folding resistance

Ability to be closely folded in two directions at right angles to each other without cracking at the resulting pointed zone.

Drain (v); draining

Set aside wet hides and skins in process, so that free liquor escapes.

Drawn grain

Wrinkled grain layer caused by the corium contracting during the tannage more than the grain layer, which therefore seems to be “drawn up”. Can be caused by excessive agitation in the process vessel or chemically. See: Pebbled grain.

Dressing

Alum, chrome, oil, vegetable, aldehyde, soap, Leipzig.

Inclusive term for all the various operations carried out on any type of rough-tanned,  tawed leather or furskin to render it fit  for use and saleable; includes currying and finishing .

Dressing hide

Unsplit rough-tanned hide, vegetable tanned in a manner giving good tensile strength and mellow feel; suitable for such purposes as harnesses and straps.

Drum

Rotating cylindrical container (usually made of wood) used in leather production.

Drum (v); drumming

Operation of a drum used in the leather processing industry.

Drum liming

Liming of hides, or skins, in a rotating drum.

Drum stuffing

Process for the introduction of grease in the molten state into damp leather, using a drum, which can be heated by hot air.

Drum tanning

Tanning hides and skins in a rotating drum specially designed for this purpose.

Dry (v); drying

Evaporate water from leather after completing the wet processes in leather manufacturing. Different drying methods are used to prepare the leather for the subsequent finishing processes.

Dry chrome bend

Flexible chrome tanned sole leather bend which has not been impregnated with wax, grease or similar agent.

Note: Mostly used for sports shoes.

Dry feel

Sensation of dryness in handling a leather.

Dry hide

Hide cured by drying from exposure to air.

Dry loading

Loading of vegetable tanned sole leather by drumming it in the washed, sammed and aired-off condition in concentrated tan liquor at c. 45 °C.

Dry salted

Cure by first treating with salt, either by application of solid salt to the flesh side or by steeping in brine and then drying. Hides cured by this method are generally salted in pile to effect an initial cure and then dried out either by spreading on the ground, hanging over a pole, or by suspension, preferably in the shade.

Dry salted weight

Weight of wet salted hides after air drying to 15% to 20% moisture.

Dry shaving

Mechanical shaving process of dried leather to obtain exact adjustment of the final thickness of leather.

Dry solid content

Defines the percentage of dry solids contained in sludge or more generally of a solid waste compared to raw material.

Dry splitting

Operation of cutting a dried hide or skin, horizontally into two or more layers, grain and flesh layers.

Dry tannage

Drum tannage carried out on wet material with little or no float, the tanning agent being added in powder or concentrated liquid form.

Dry wheeling

Mechanical process generally suitable for soft leather, chamois and woolskins. The skins are passed across a rotating wheel which is coated with glue and dusted with the appropriate grade of carborundum or other suitable abrasive.

Dry-brined hide

Hide which has been cured by a short immersion in a brine solution and then dried out.

Dryer

Equipment used for the elimination of water by evaporation.

Drying chamber

Heated and ventilated chamber in which the leather remains stationary until dry.

Drying oil

Fatty oil which forms a hard film when a thin layer is exposed to air.

Drying tunnel

Drying in tunnels with supply of circulated hot air. Quick drying method by a throughfeed system with or without separate temperature zone sectors.

DS

See: Dermatan sulphate.

DSC

See: Differential Scanning Calorimetry.

Dubbin

Mixture of fish oil and wax used to impart waterproofness to bridle and harness leathers.

Dull (v); dulling

Make or become dull, or sad, incorporating a complementary colour in the dyeing mixture.

Dump (v); dumping

1. Dispose of waste.

2. Send goods that are unsaleable at high price in the home market to foreign markets for sale at lower prices, to avoid lowering the home market price.

Dung

Hides of animals can be crusted with caked manure containing excrement, straw, shavings and other chemicals. This can cause bacterial damage to the hide or skin.

Dye

Colouring substance, especially in solution. A colour or tint produced by dyeing.

Dye (v); dyeing

Impregnate a desired colour to the surface of a material, and more or less throughout its thickness, by treatment with a solution of a dyestuff or of a substance capable of conversion to a dyestuff.

Dye bath

Bath or liquor, in which a material is dyed, that contains dye, dyeing auxiliaries, and chemicals.

Dye fixing agent

Substance to increase the fastness of the dye material.

Note: A cationic substance in the case of anionic dyes.

Dye spectrum

Image obtained of the distribution of light intensity of different wavelengths of a transmitted beam of light through a solution of dye (absorbance spectrum).

Dye to pattern

Apply an appropriate blend of dyestuffs to a material to obtain and duplicate the same colour as that of a sample in any kind of material.

Dyeing affinity

Capability of a material to combine with dyes.

Dyeing auxiliary

Substance which has positive effect on dyeing stage.

Dyeing drum

Rotating drum to dye hides and skins.

Dyeing power

Ability to dye a material with a colour, which is intense in relation to the amount of the dye used.

Dyestuff

Substance used for dyeing, which yields a dye.

Dyestuff ion

Ion, molecule or radical of a dyestuff which is responsible for its dyeing ability.

Dyewood extract

Concentrated extract of dye contained in wood, such as logwood.

Dynamic waterproofness

Evaluation of waterproof properties in dynamic conditions. The leather to be tested is flexed in water rather than just being placed in water in a static state with no movement - hence the term “dynamic”