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Damp leather
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Leather with approximately 50%
to 60% moisture content.
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Damp stuffing
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Introduction of more or less
liquid grease into damp leather by hand and/or drumming.
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Damping plant
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See: Conditioning plant.
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Daphnia
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Micro shellfish used to determine
the toxicity of water.
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Dappling
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Patchy
appearance to surface pigment finish due to uneven penetration
in certain areas of the grain. Often caused by damaged enamel.
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Deacidify
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Removal of acid or
a process of reducing acidity.
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Deamidation
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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).
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Decantation
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Draining off the supernatant
liquor after settling of suspended solids.
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Decarboxylase
|
Enzyme capable of
removing the carboxyl group from a carboxylic acid or an amino
acid.
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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.
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Decolourise (v); decolourising
|
Deprive, bleach or remove the
colour from a material, by chemical treatment or sunlight and
weather effect.
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Dedust (v); dedusting
|
Remove dust from the surface
of leather which is produced when leather is buffed. See: Air
blast; brush (v); brushing
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Defoamer
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Finishing auxiliary used to avoid
foaming of finish preparations. Especially used in finishing
applications like curtain coating and roller coating.
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Deformability
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Ability to allow
a permanent change in shape, when subjected to stress, without suffering damage, as in shoe lasting.
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Degrain
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Remove the grain of a leather
by mechanical processes such as splitting, shaving or buffing.
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Degras
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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.
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Degrease (v); degreasing
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To remove grease by any method.
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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.
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Degree of dispersion
|
Proportion of the material particle
sizes in a colloidal solution, which exist in the form of smaller,
rather than larger.
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Degree of dullness
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Proportion of the incident white
light which is absorbed by a coloured material.
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Degree of penetration
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Depth to which chemicals
such as dyestuff, fat, resin, etc. penetrate into the leather.
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Degree of plumping
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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.
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Degree of saturation
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Percentage of the incident light
of any wave length which is reflected, emitted, and/or scattered
by a coloured material.
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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 .
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Degree of swelling
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Measure of the degree to which
a protein is swollen by the uptake of water, expressed, for
example, as percentage increase in weight.
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Dehydration
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Removal of water.
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Delamination
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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.
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Delayed salting
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Salting which has been delayed
for so long a period after flaying that damage may have been
caused through putrefaction, etc.
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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.
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Deliming power
|
Ability of an agent to neutralise
the lime of pelts introduced into it.
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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.
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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.
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Denaturation
|
Modification of the
protein’s natural molecular structure produced by heating or
treating it with chemicals, thus modifying its original properties.
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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.
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Density
|
The mass of a given volume of
the actual leather fibre.
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De-olation
|
Cleavage of links between two metal ions in a polynuclear
complex ion, under the action of acid.
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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.
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Depilation
|
Removal of hair or wool from
hides or skins by any method.
See: Unhair (v); unhairing
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Depilatory
|
Chemical, or preparation, which
destroys hair or wool or loosens its attachment to the skin.
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Depth of shade
|
Degree or intensity of required
colour. Achieved by careful control of neutralising, retanning,
choice of dyestuff and fixation.
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Derma
|
The protective integument of
the living (animal) body organs.
See: Dermis.
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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’).
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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.
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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.
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Desorption
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Process of removing
a sorbed substance by the reverse of adsorption or absorption.
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Deswelling
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Reduction of the water content
in swollen hides and skins by means of chemicals.
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Detan (v); detanning
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Removal of more or less of the
tanning agent from leather.
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Determination of acidity
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Determination of
the total amount of acids in a solution or a material by titration
with alkali.
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Dewool (v); dewoolling
|
Removal of previously loosened
wool from woolled sheepskin.
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Dewoolling knife
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Double-handled, concave, blunt
scraper for removing the wool from sweated or painted sheepskins.
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Diamond-buffing leather
|
Stout, vegetable-tanned leather
made from the hides of pachedermatous animals (elephants and
walruses) used for cutting and polishing diamonds.
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Diazo group
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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.
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Diazotise (v); diazotisation
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Convert the amino-groups of an
aromatic compound to azo-groups (-N=N-) by treatment with nitrite
and acid.
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Dichloromethane soluble substances
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Substances being
extractable by dichloromethane from a leather (mainly fats and
oils and also resins and other chemicals used in the finishing
process).
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Differential Scanning Calorimetry (DSC)
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Technique for measurement
of, and comparison (differential) of, process heats (reaction,
absorption, hydrolysis, etc.) for a specimen and a reference
material.
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Digestion
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Mineralisation of sludge and
organic waste by anaerobic fermentation, accompanied by the
production of methane gas.
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Diluent
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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.
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Dilutable
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Ability of an agent or a solution
to be diluted by other agents or mixtures.
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Dip
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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.
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Dip dyeing
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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.
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Dip dyeing
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Dyeing of furskins by dipping
in the dye bath.
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Dip stuffing
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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.
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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.
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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.
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Discolour (v); discolouring
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Become stained, faded, spoiled,
or change colour of a surface.
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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.
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Disinfectant
|
Chemical which, in suitable concentration,
will kill micro-organisms.
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Disperse dyestuff
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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.
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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.
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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.
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Dissolved organic carbon
|
Mass concentration of substances
remaining after filtration according to clearly defined conditions.
Expressed in mg/l or g/m3.
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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.
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Dissolved solids
|
Mass concentration of substances
remaining after the filtration of a sample and dry evaporation;
it is determined in precisely defined conditions.
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DO
|
See: Dissolved oxygen.
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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.
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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.
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Domestic hides
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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”.
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Domestic market
|
The opportunity to buy or sell
in one’s own country. Pertaining to one’s own country or nation.
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Dongola tannage
|
Combination tannage with alum,
followed by cutch or gambier, or vice-versa.
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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.
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Double face
|
A woolled sheepskin, finished
on the flesh side (suede or nappalan), used for sheepskin coats,
etc.
See: Shearling; sueded woolled sheepskin.
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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.
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Double-folding resistance
|
Ability to be closely
folded in two directions at right angles to each other without
cracking at the resulting pointed zone.
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Drain (v); draining
|
Set aside wet hides and skins
in process, so that free liquor escapes.
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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.
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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
.
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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.
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Drum
|
Rotating cylindrical container
(usually made of wood) used in leather production.
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Drum (v); drumming
|
Operation of a drum used in the
leather processing industry.
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Drum liming
|
Liming of hides, or skins, in
a rotating drum.
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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.
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Drum tanning
|
Tanning hides and skins in a
rotating drum specially designed for this purpose.
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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.
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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.
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Dry feel
|
Sensation of dryness
in handling a leather.
|
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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.
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|
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.
|
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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.
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|
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
|
