This section is from the book "The Manufacture Of Boots And Shoes: Being A Modern Treatise Of All The Processes Of Making And Manufacturing Footgear", by F. Y. Golding. Also available from Amazon: The Manufacture Of Boots And Shoes.
When a skin is pulled, the line or direction in which it gives or stretches most is technically known as the "line of stretch." This property varies in the several kinds of skins, and also in the same class of skin if tanned or dressed differently. The directions in which the skin yields least when pulled or strained, or are relatively tightest, are termed the ."lines of tightness." There is not much variation in the general lay out of the lines of tightness in the skins of various animals, but the substance, quality, and mode of tanning will determine largely the amount of notice that must be taken of the relative stretch and tightness in the skin, and how far these properties will influence the cutting up. When cutting leathers that are very firm, or when cutting the primest portions of the skin, it is not so necessary that such a strict adherence to the lines of tightness be maintained when placing the patterns on the skin. But with stretchy leathers, or when the inferior portions are reached, if a fairly good skin, great care must be taken to so arrange the patterns on the material, that the best results are obtained in the produced goods. It does not necessarily mean any great sacrifice of economy to carry this principle into effect. The great point, even in cheap work, is to pair or mate up the work, paying due regard to the tightness and stretch of the material, so that they stretch on opposite sides of a pair, in a similar way or direction.
The stretch or "lines of stretch " pull across the " lines of tightness," and in a diagram form Fig. 177 will give this relation,* where the arrow lines indicate the "lines of tightness," and the circular lines cutting them the "lines of stretch."
A good deal of speculation is prevalent as to the cause of the skin being relatively tighter in a given direction, some even affirming that the " lines of tightness " are determined by the direction or lay of the hair. But it seems as though the cause for the relative definite direction of the tightness of the skin is the same cause for the lay or direction of the hair. Experts do not agree as to the direction of the " lines of tightness," some making them radiate from the backbone line at about an angle of 60 degrees to the flanks, while those to the shank start from the same position as diagramized in Fig. 177, while others prefer to indicate the direction by using a mode similar to Fig. 178. The cause of the relative tightness being ascertained, the direction in which the skin is tight will be the better determined. From the brief remarks given concerning the structure of the skin, and more fully by reference to the chapter dealing with the bottoming leathers, it will be understood which kind of fibre gives the elastic or stretching property. The animal locomotion and movement will determine the proportion and position of these fibres, and by examining a muscular view of the animal after the skin has been removed, the cause of the tightness and stretch is suggested. In Fig. 179 we give a view of an ox with the skin removed.
Methods of Disposing. - Having determined the direction of the greatest tightness, the best way to place the material tight in boots and shoes should next be considered. Boot and shoe uppers may be cut so that the direction of greatest tightness may be from (a) heel to toe, i.e. from counter to toe, (b) in the line of the seams, or (c) tight across from vamp edge to vamp edge. The former is termed "tight to toe," and is the one mostly adopted. The second mode of disposing of the direction of the greatest tightness is termed " tight seam," and is resorted to in a few bespoke houses and with stretchy material when lasted upon a method which demands much "horsing" or "hoisting" of the uppers. The third method is used with an idea of preventing the upper "treading over"! during wear, but is unreliable for work that is to be toe-capped, etc., or where the grain or colour cannot withstand the pulling-over strain. The vamp marked with an arrow in Fig. 171 will demonstrate the cutting of vamps "tight-across;" also A in Fig. 173 illustrates how a front on this principle should be cut. The back marked B in Fig. 174 illustrates the way the seam should pull tight if cut upon the "tight-seam" principle. The usually adopted "tight-to-toe" method is illustrated in Figs. 167, 173 A, 174 B, and 175.
* This diagram is given only to indicate the differences between the " lines," and not to indicate their absolute direction.