Vacuum drying

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.

Valonia

Acorn cups of certain oaks

Note: Greek evergreen oak, Quercus Aegilops (Morea, the Greek Archipelago, Asia Minor) and the arcadian oak, Q. macrolepis (Greece). 

Varnish

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.

Vat

Water-tight vessel, of wood, brick, concrete, etc., usually above ground level, for storing liquids, preparing solutions, giving liquid treatments, etc.

Vat curing

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.

Vat dyestuff

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.

Vegetable tannage

Tannage by means of the tanning agents contained in the barks, woods, fruits, leaves, etc., of plants.

Vegetable tanned

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.

Vegetable tanned sole leather

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.

Vegetable tannin

Tanning agent contained in, and obtained by, the extraction of the barks, fruits, galls, leaves, roots or wood of certain plants.

Veininess

A prominent vein pattern in hides which becomes visible in the finished leather, often due to poor bleeding which encourages bacterial growth.

Veins

Tube through which blood circulates in an animal body. When visible in leather the cause is usually poor bleeding or staleness. See: Blood vessels.

Veiny

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.

Vellum

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.

Velvet leather

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.

Vertical fibre

Loss of substance during wet processing due to vertical fibre effect, leads to a “cauliflower” like pattern on the flesh side.

See: Cauliflower effect.

Viscosity

Property of fluids that indicates their resistance to flow.

Viscosity-regulating agent

Agent used in finish formulations to regulate the viscosity of a finish. Note: Thickener or thinning agent.

VOC

See: Volatile Organic Compound.

Volatile matter

Matter readily given off by evaporation, such as solid matter that can be given off as gas or steam by heating.

Volatile Organic Compound (VOC)

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.

Vulcanisation

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.