G.A.G.

See: Glycosaminoglycans.

Gall (nut, apple)

Pathological growth produced on the leaves, buds or fruits of various trees, especially oaks, by the action of various insects, particularly of the genus Cynips.

Gall wasp

Wasp of the genus Cynips, causing the growth of galls.

Gallotannin

Class of vegetable tannins which are esters of phenol carboxylic acids, chiefly gallic, m-digallic and related acids, with polyhydric alcohols and sugars such as glucose; readily hydrolysed into their components.

Garment leather

See: Clothing leather.

Gas Chromatography (GC)

Separation technique involving passage of a gaseous moving phase through a column containing a fixed phase; it is mainly used as a qualitative and quantitative analytical technique for volatile compounds.

Gas meter leather

Leather capable of being rendered air-tight by impregnation with oils and used for diaphragms in gas meters.

GC

See: Gas Chromatography.

GC-ECD

See: Electron Capture Detector Gas Chromatography.

GC-MS

See: Mass Spectrometry Detector Gas Chromatography.

Gear leather

See: Harness leather.

Gel filtration

Type of chromatography which separates molecules on the basis of size; higher molecular weight substances pass through the column first. Also known as molecular exclusion chromatography; molecular sieve chromatography.

Gelatine salt test

Test to check the presence of a vegetable tannin in a solution by adding a gelatine solution containing salt

Gelatine

Water-soluble, gel-forming protein, prepared from collagen by extracting limed and delimed skin pieces or ossein (degreased and decalcified bone) with hot water; the process involves shortening and uncoiling of the polypeptide chain.

Geometrisation

To trim effectively at the earliest possible point in manufacture to minimise waste and optimise yield.

See: Trim (v); trimming.

Glacé goat

Leather made from goat skin finished as glacé kid with a smooth, glossy grain surface but semi-chrome or vegetable tanned.

Note: In Italy, this leather may be chrome tanned, synthetic tanned or alum tanned.

Glacé kid

Upper leather made from kid or goatskin by a full chrome tanning process and given a smooth, bright, glossy finish.

In France and Germany the tannage is the two-bath process.

In Holland and the UK also called glazed kid.

See: Gloving Kid.

Glacé kid

When applied to gloving leather a synonym of gloving kid.

Glacé leather

Straight dyed grain gloving leather, especially on the continent of Europe.

See: Gloving kid.

Glacé leather

Leather finished on the grain side with a bright, smooth, glossy or glasslike surface obtained, according to the type of leather, by glazing, plating, ironing or polishing.

See: Glacé goat; glacé kid.

Glacé tanning

Tawing, or dressing, with a mixture of alum, or aluminium sulphate, salt, egg yolk and wheat flour.

Gland

Any cell or organ which synthesises and secretes some particular chemical substance for use by the body or for excretion.

See: Phospholipids.

Glass cylinder

Fixed glass cylinder in the working head of a glazing machine which imparts a high gloss to previously coated leather by rapidly moving across the leather surface under high pressure.

Glass plate

Glass plates in frames which are used in the paste-drying process. A glass plate is covered with a thin starch paste and the wet leather is slicked out on this, grain side to the glass, to which it adheres, thereby preventing shrinkage on drying.

Glaze (v); glazing

Operation carried out by a glazing machine to impart a high gloss to previously coated leather. A glass or agate roller is pushed with frictional pressure over the leather surface in rapid sequence.

Glazing cylinder

Fixed glass or agate cylinder in the working head of a glazing machine which imparts a high gloss to a previously coated leather by rapidly moving across the leather surface under high pressure.

Globulin

Any of a class of simple proteins with little or no solubility in water, but soluble in salt solutions. Globulins are extracted to a great extent by salt preservation of hides. With the increase in fresh hide processing, the blood protein of the clotted blood in hematomas could cause stain problems during leather making (haemoglobin iron + unhairing sodium sulphide).

Gloss

Lustre of a polished surface, which gives a superficially attractive appearance, by reflecting  a high proportion of incident light.

Glove leather

See: Gloving kid.

Gloving kid

Soft grain gloving leather, capable of being considerably stretched without springing back. In the strict sense made from kid skin tawed, or tawed and subsequently chrome tanned or simply chrome tanned.

Note: Sometimes called Glacé kid.

In the UK sometimes applied to leather made from lambskin. In Spain the leather is mainly chrome tanned.

Glucogallin

Ester of one molecule of gallic acid and glucose, such as

D-glucogallin, first isolated from Chinese rhubarb and occurring in tara, myrabolams and eucalyptus extracts and formed by breakdown of several gallotannins.

Glue

Impure form of gelatine obtained by extracting bones or glue-stock with hot water.

Glue-stock

Trimmings from untanned hides and skins and fleshings, used in the manufacture of gelatine and glue.

Glutaraldehyde

Dialdehyde, OHC.(CH₂)₃.CHO. Can be used as a solo, pre or re-tanning agent for all types of leathers. Improves wash, perspiration and alkali resistance.

Glutaraldehyde leather

Modified glutaraldehyde pre-tannage given to hides or skins prior to the main tannage.

Note: Combination chamois.

Glyceride (mono-,di-,tri)

Ester of glycerol with respectively one, two or three esterified

(–OH) hydroxyl groups.

Glycerol

Trihydric alcohol, CH₂(OH)CH(OH)CH₂OH.

Glycoprotein

Member of a group of animal conjugated proteins containing as prosthetic groups one or more saccharides with a relatively low number of sugar residues, covalently bound to the protein moiety; occur in connective tissues and include certain globular proteins.

Glycosaminoglycans (G.A.G.)

Glycosaminoglycan (G.A.G.) is any of a group of polysaccharides which contain aminosugar residues. G.A.Gs are often found in complexes with protein molecules as proteoglycans and include heparin, chondroitin, hyaluronic acid, blood substances and  dermatan sulphate (DS).

Glyoxal

Dialdehyde, OHC.CHO, which tans in fairly concentrated solutions of alkali carbonates and bicarbonates, giving a light, tan-coloured, flexible leather.

Goat skiver

Tanned grain split of a goat skin.

Goatskin

Skin from a goat with straight hairs, in contrast to one from a goat with woolly hair such as Angora, Kashmir and other types.

Gold leather

Leather with a gold-coloured metallic surface. The metal may be gold or a gold-coloured alloy or a white metal in conjunction with a tinted lacquer. The metal may be applied in the form of leaf or foil or as a finely divided powder suspended in lacquer.

Note: Mainly produced from goat or kid skins or sheepskins.

Grade

Position in a scale of size, quality, or intensity.

Grain

Outer surface pattern of a hide or skin which includes the hair follicles and pores just beneath the thin layer of epidermis. During the unhairing process the epidermis is removed and the underlayer becomes the grain surface.

On finished leather, the nature and design of the surface.

Grain (v); graining

See: Board (v); boarding.

Grain absorptivity

Ability of the grain surface of a leather to take up a solution or liquid.

Grain break

Grain break is the pattern of tiny wrinkles formed when the leather is bent grain inwards. The causes of poor, or coarse break can be due to stale raw material or processing defects. See: Break.

Grain burst

Fissure, or break, in the grain layer of a leather.

Grain cracking

Formation of cracks in the grain surface of leather under the stresses of pulling or bending, as in lasting.

Grain distension

Elongation of the grain when pulled or stressed.

Grain dyeing

Dyeing of the grain layer of a full grain leather.

Grain embossing

Form an artificial grain on the surface of a leather by pressure from a heated engraved plate or roller.

Grain impregnation

Agents to improve the break by tightening the grain surface and reducing any excessive absorbency capacity. Special pre-treatment of the leather before the application of a polishing agent or the base coat.

Grain layer

The portion of a hide or skin extending from the surface exposed by removal of the hair or wool and epidermis down to about the level of the hair or wool roots.

Grain oil (v); grain oiling

Application of an oil to the grain surface of leather to protect the surface from darkening by oxidation during the drying process, or to protect a finished leather.

Grain pattern

Pattern presented by the surface of the dermis of the hide or skin after removal of the epidermis and hair or wool, or pattern of the finished leather.

Grain split

The grain layer of a hide or skin obtained by splitting it into two or more layers.

Grain tightness

Firm attachment of the grain layer of a leather to the underlying dermis, shown by the absence of wrinkles when the leather is fixed grain inwards.

Grained leather

Leather whose natural grain pattern has been developed by boarding or which has had a grain pattern impressed upon it.

See: Board (v); boarding; boarded grain.

Grasser skin

Calfskin or kip taken from an animal which has been fully weaned to a green diet, characterised by coarseness of grain.

Grease

General term for a solid or semi-solid material with certain fatty properties, such as feel, which may be a single material or a blend of various oils, fats, soaps, etc., used for such purposes as stuffing leather and lubrication.

Grease (v); greasing

Introduce grease into a material or apply it to the surface.

Grease mark

Dark, fairly extensive area on leather, especially over the kidney or backbone area due to excessive concentrations of natural grease.

Grease topping

Grease preparation applied to a finished leather to give it special properties.

Note: Properties such as gloss, water-repellency, etc.

Greased nubuck

See: Pull up effect.

Greasy paste

Greasy mixture used to spread on the surface of certain leathers.

Note: Used to impart waterproofness in bridle and harness. See: Dubbin

Green flesh (v); green fleshing

Flesh hides or skins before liming.

Green fleshings

Small pieces of connective and adipose tissues cut from the inner surface of hides and skins in the fleshing operation (after soaking).

Green hide

More or less fresh, uncured hide as flayed from an animal.

Green weight

Weight of the hide as it is removed from the carcass and trimmed at the time of flaying, before any evaporation has begun.

Grey scale

Series of achromatic tones having varying proportions of white and black to give a full range of greys between white and black; also in a grey/black scale. A grey scale is usually divided into 5 steps with half divisions. (e.g. 1, 1/2, 2, 2/3, 3 etc.) Usually used for the evaluation of colour change or transfer (e.g. 5 = no colour change,  1 = high colour change). The white to black grey scale is used to assess staining (colour transfer) and the grey/black scale is used to assess the change in colour.

Grey shimmer

Undesirable surface effect of a leather caused by uneven refraction of light especially on leather with coarse hair pores, dark coloured finishes or in leather with very thin finish coat.

Grid

Plate, formed of a system of crossed parallel bars or wires, over which leather is stretched for drying.

Grin (v); grinning

Formation of paler, or grey looking, parallel fine crevices when the leather is stretched or bent grain outwards, owing to the rupture of the pigmented finish coat.

Grind (v); grinding

Grinding bark or other vegetable tanning material.

Grinder

Device with grinding wheel for sharpening the knife blades of splitting machine, shaving machines, etc.

Grinding wheel

A rotating grindstone for sharpening a knife as in the splitting machine, shaving machine, etc.

Ground (v); grounding

Applying of a base coat to leather, to block the pores, before

applying the true finish coats.

Ground substance

Amorphous material containing acid mucopolysaccharides, such as chondroitin sulphate, in which the fibres and cells of connective tissues are embedded; certain constituents are concerned with the growth of collagen fibres. 

Ground tan-bark

Tannin-containing bark, especially oak and pine barks, ground ready for use.

Ground tanning material

Vegetable material, such as barks, fruits or woods, reduced to small fragments for leaching or for use in layers.

Growthiness

Grain wrinkles, or fat wrinkles, seen as depressed valleys on the grain surface, mostly the neck and radiating at right angles from the backbone. Growthiness is an inherent characteristic of skins and hides and can only be minimised by processing and mechanical actions.

Guard

Part of a machine specially used to provide protection by means of a physical barrier. Depending on its construction, a guard may be called casing, cover, screen, door, enclosing guard, etc.

Gypsum stain

Darker and harder area on the leather surface due to the deposition of insoluble calcium and magnesium salts (phosphate), formed by the interaction of calcium and magnesium compounds in the curing salt and phosphate derived from bacterial action on blood and/or muscle tissues.