The Vegetable Tanning Process - A Collection of Historical Articles on Leather Production. Various
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The Vegetable
Tanning Process
A Collection of Historical
Articles on Leather
Production
By
Various Authors
Copyright © 2011 Read Books Ltd.
This book is copyright and may not be
reproduced or copied in any way without
the express permission of the publisher in writing
British Library Cataloguing-in-Publication Data
A catalogue record for this book is available from
the British Library
Leather Crafting
Leather is a durable and flexible material created by the tanning of animal rawhide and skin, often cattle hide. It can be produced through manufacturing processes ranging from cottage industry to heavy industry, and has formed a central part of the dress and useful accessories of many cultures around the world. Leather has played an important role in the development of civilisation from prehistoric times to the present, and people have used the skins of animals to satisfy fundamental (as well as not so essential!) needs such as clothing, shelter, carpets and even decorative attire. As a result of this importance, decorating leather has become a large past time. Leather crafting or simply leathercraft is the practice of making leather into craft objects or works of art, using shaping techniques, colouring techniques or both. Today, it is a global past time.
Some of the main techniques of leather crafting include:
Dyeing - which usually involves the use of spirit- or alcohol-based dyes where alcohol quickly gets absorbed into moistened leather, carrying the pigment deep into the surface. 'Hi-liters' and 'Antiquing' stains can be used to add more definition to patterns. These have pigments that will break away from the higher points of a tooled piece and so pooling in the background areas give nice contrasts. This leaves parts unstained and also provides a type of contrast.
Painting - This differs from leather dyeing, in that paint remains only on the surface whilst dyes are absorbed into the leather. Due to this difference, leather painting techniques are generally not used on items that can or must bend, nor on items that receive friction, such as belts and wallets - as under these conditions, the paint is likely to crack and flake off. However, latex paints can be used to paint flexible leather items. In the main though, a flat piece of leather, backed with a stiff board is ideal and common, though three-dimensional forms are possible so long as the painted surface remains secured. Unlike photographs, leather paintings are displayed without a glass cover, to prevent mould.
Stamping - Leather stamping involves the use of shaped implements (stamps) to create an imprint onto a leather surface, often by striking the stamps with a mallet. Commercial stamps are available in various designs, typically geometric or representative of animals. Most stamping is performed on vegetable tanned leather that has been dampened with water, as the water makes the leather softer and able to be compressed with the design. After the leather has been stamped, the design stays on the leather as it dries out, but it can fade if the leather becomes wet and is flexed. To make the impressions last longer, the leather is conditioned with oils and fats to make it waterproof and prevent the fibres from deforming.
Molding and shaping - Leather shaping or molding consists of soaking a piece of leather in hot or room temperature water to greatly increase pliability and then shaping it by hand or with the use of objects or even molds as forms. As the leather dries it stiffens and holds its shape. Carving and stamping may be done prior to molding. Dying however, must take place after molding, as the water soak will remove much of the colour. This mode of leather crafting has become incredibly popular among hobbyists whose crafts are related to fantasy, goth / steampunk culture and cosplay.
Contents
The Making of Leather. Henry R Proctor
Charles Thomas Davis
Pocket Manual for the Dyeing of Garments, Leather, Furs and Sundry Materials. Anon
Tanning Processes. August C Orthmann
The Chemistry of Leather Manufacture.
George D Maclaughlin and R Theis
THE VEGETABLE TANNING MATERIALS
THE tannins may be described as a class of substances found in many plants, which have the common properties of precipitating gelatine from solution and of converting skin into leather. They are all colloid, that is uncrystallisable, and for this reason few of them have yet been obtained in a pure form. They are feebly acid, and are sometimes called “tannic acids,” but it is uncertain whether they are strictly acids, since many phenols, of which “carbolic acid” is a type, have also slightly acid properties. All natural tannins1 are benzene derivatives, either from the dihydric phenol catechol, or the trihydric phenol pyrogallol, and another trihydric phenol phloroglucol is also often present. The positions of the OH groups are shown by the following diagram, the carbon atoms at the other angles being combined with H.
They are consequently usually divided into “catechol” tannins giving green-blacks with iron salts, and “pyrogallol” tannins giving blue-blacks, and often used as inks; but it is certain that the distinction lies deeper, and is rather one of structure than of the particular phenol. The two classes, however, whatever the cause, possess a marked difference in tanning properties, the iron-blueing tannins causing a white deposit of crystallised ellagic acid in the leather while the iron-greening (with a few giving violet-blacks) deposit dark brown substances called “reds” or “phlobaphenes.” Whether these are in all cases products of the tannins themselves, or rather of other bodies associated with them, is still doubtful.
The tannin-yielding materials are so numerous that but very few, even of those in commercial use, can be mentioned here. The oldest and formerly the most important in this country is the bark of the oak, usually stripped in spring when the sap has begun to rise, because at this time the bark is more readily separated from the trunk. It is a somewhat weak material, only yielding 10—12% of substances absorbable by hide, but it has the peculiarity that good leather of almost all descriptions, both light and heavy, can be made by its use. Very little leather is now tanned exclusively with oak-bark, though other oak products are largely used. Oak wood also contains tannin, though in less quantity than the bark; but by chipping and hot extraction, and subsequent decolorisation and concentration of the infusion by evaporation, an extract of 25—30% is obtained, and is now made from the waste wood and sawdust in very large quantity in Slavonia and Northern Italy, where oak is still abundant. An extract hardly to be distinguished from that of oak wood is made from the wood of the edible chestnut Castanea vesca. The oak principally used in Europe is Quercus robur (with its sub-species Q. scssiliflora and Q. pedunculata) but most oaks contain tannin. Very important is the large bearded cup of the acorn of evergreen oaks from Greece and the Levant known as valonia, which is extremely rich (30—40%) in tannin, and largely imported. Oak-galls (from Q. infectoria) are a source of the druggists’ “taimic