The Vegetable Tanning Process - A Collection of Historical Articles on Leather Production

Various

Description

This book contains classic material dating back to the 1900s and before. The content has been carefully selected for its interest and relevance to a modern audience. Carefully selecting the best articles from our collection we have compiled a series of historical and informative publications on the subject of leather. The titles in this range include "A Guide to the Decoration of Leather" "Tools for Leatherwork" "Tools for Leatherwork" and many more. Each publication has been professionally curated and includes all details on the original source material. This particular instalment, "The Vegetable Tanning Process" contains information on the methods and equipment used in leather production. It is intended to illustrate the main aspects of vegetable tanning and serves as a guide for anyone wishing to obtain a general knowledge of the subject and understand the field in its historical context. We are republishing these classic works in affordable, high quality, modern editions, using the original text and artwork.

Informations

• Publié par: Read Books Ltd.
• Date de parution: 17 septembre 2020
• Nombre de lectures: 0
• EAN13: 9781528764384
• Langue: English
• Poids de l'ouvrage: 1 Mo

Extrait

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
The Manufacture of Leather - Being a Description of All of the Processes for the Tanning, Tawing, Currying, Finishing and Dyeing of Every Kind of Leather .
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
T HE 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 tannins 1 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 acid, but unimportant as a tanning agent, though the often repeated statement that the so-called pathological tannins from insect galls will not make leather is absolutely without foundation. It is somewhat curious that these oak tannins are by no means chemically identical. The bark-tannins distinctly belong to the class we have called catechol tannins, though that of the common oak contains some mixture which gives blue-black with iron and produces bloom. The wood tannins belong to the pyrogallol class, and the gall tannin is the typical gallotannic acid which is a pure pyrogallol derivative.
Another important material of the pyrogallol class is myrobalans (30-40%), the dried fruit of an Indian tree, and divi-divi, the pod of C salpinia coriaria , a tree allied to logwood (40-50%) and sumach, the leaves of Rhus coriaria (25-30%), while the most important sumach adulterant, Pistacio lentiscus , is a catechol tannin.
To the catcchol class belong also gambier, an extract from the leaves of Uncaria gambia (30-40%); the bark of the Australian mimosa or wattles (25-40%); quebracho extract from the very hard wood of a South American tree (dry 60-70%) and many others. It will be noted that all these materials are very much richer in tannin than oak-bark, and it is to the stronger liquors obtained from them, rather than to any chemical tanning, that the shortened time of modern sole-leather tannage is due. Whether the shortened process gives so durable a leather as the older method may be questioned, but the leather is honestly and thoroughly tanned with mixtures of natural tannins very closely approximating to that of oak-bark; while in the old process much time was positively wasted by ignorant mismanagement.
The way in which tannins tan and the chemical nature of the leather formed still need elucidation. The view most probable at present is that leather is rather a colloidal than a strictly chemical compound. The tannins all yield colloidal solutions, and gelatine and hide-fibre are typical colloids. It has been shown in the author s laboratory and elsewhere that, in presence of the trace of acid essential to tanning, the particles of tannin have opposite electrical charges to those of gelatine, and it is well known that two colloid solutions in which this is the case, when mixed, are mutually precipitated as a colloidal compound.
Although not strictly vegetable materials, the synthetic tannins recently discovered by Dr Stiasny must be menti