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Vacuum drying
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Drying
technique in which the wet leather is spread out by hand grain
down on a polished, heated metal plate. An airtight hood equipped
inside with a felt and a wire net is placed over the leather
before a vacuum is applied. Depending on the preset vacuum,
the temperature of the metal plate and the thickness and moisture
content of the leather, the wet leather is dried in about 4
to 10 minutes.
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Valonia
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Acorn cups of certain oaks
Note: Greek evergreen oak, Quercus
Aegilops (Morea, the Greek Archipelago, Asia Minor) and the
arcadian oak, Q. macrolepis (Greece).
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Varnish
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A solution of a film-forming
substance, based on a natural resin, nitrocellulose or a boiled
drying oil, in organic solvents, which, by evaporation of the
solvents and/or chemical changes, leaves a more or less transparent,
hard, flexible and glossy protective film on the surface to
which it is applied.
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Vat
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Water-tight vessel, of wood,
brick, concrete, etc., usually above ground level, for storing
liquids, preparing solutions, giving liquid treatments, etc.
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Vat curing
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Method of curing in which hides
are laid one by one in a pit and covered by salt, the pit being
finally filled with brine.
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Vat dyestuff
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Complex of organic molecules
that are insoluble in water, but when their carbonyl groups
are properly reduced in a solution of caustic soda and sodium
hydrosulphite to the so-called leuco or soluble state, they
exhibit an affinity for cellulosic fibres.
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Vegetable tannage
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Tannage by means of the tanning
agents contained in the barks, woods, fruits, leaves, etc.,
of plants.
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Vegetable tanned
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Tanned exclusively with vegetable
tanning agents or with such materials together with small amounts
of other agents, used merely to assist the tanning process or
to improve or modify the leather, and not in sufficient amounts
to alter notably the essential character of the leather.
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Vegetable tanned sole leather
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Vegetable tanned sole leather
produced primarily for the manufacture of new footwear. It is
usually lighter in substance and more flexible than leather
used for the repair of footwear.
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Vegetable tannin
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Tanning agent contained in, and
obtained by, the extraction of the barks, fruits, galls, leaves,
roots or wood of certain plants.
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Veininess
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A prominent vein pattern in hides
which becomes visible in the finished leather, often due to
poor bleeding which encourages bacterial growth.
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Veins
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Tube through
which blood circulates in an animal body. When visible in leather
the cause is usually poor bleeding or staleness. See: Blood
vessels.
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Veiny
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Leather in which the pattern
of the blood vessels is visible, or unusually prominent, on
the grain or flesh side, usually through use of stale hides
or skins.
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Vellum
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A translucent or opaque skin
material, having a smooth surface, suitable for manuscripts,
bookbinding and other purposes. Made from calf, sheep and other
unsplit skins by drying the dehaired, limed skin without applying
any tannage, the material being thoroughly cleansed and degreased
and the grain surface being smoothed during the process. The
best vellum is made from calf and in France only this is used
for vellum.
See: Parchment.
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Velvet leather
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Type of suede leather, with a
fine, velvet-like nap produced usually on the grain side.
Note: Sometimes (in Germany and
the UK always) restricted to leather from unsplit skin, or grain
split, with a nap produced by abrading the grain surface, in
contrast to suede leather produced by abrading the flesh surface.
In France this finishing process is generally done on the flesh
side; exceptions are mocha, nubuck and doeskin.
See: Suede; mocha; nubuck.
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Vertical fibre
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Loss of
substance during wet processing due to vertical fibre effect,
leads to a “cauliflower” like pattern on the flesh side.
See: Cauliflower effect.
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Viscosity
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Property of fluids that indicates
their resistance to flow.
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Viscosity-regulating agent
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Agent used in finish formulations
to regulate the viscosity of a finish. Note: Thickener or thinning
agent.
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VOC
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See: Volatile Organic Compound.
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Volatile matter
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Matter readily given off by evaporation, such as solid matter that
can be given off as gas or steam by heating.
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Volatile Organic Compound (VOC)
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Large family of carbon-containing
compounds which are emitted or evaporated into the atmosphere
and can take part in photo-chemical reactions in the air. Some
of them are toxic. In the tanning industry they are produced
from solvent evaporation in the finishing operations.
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Vulcanisation
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To render natural or synthetic
rubber harder and more resistant to heat and solvents by chemical
means, especially by heating it with sulphur and accelerators.
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