On the other hand, many cloths are produced in which the weave structure or build of the fabric is of vital importance: in which the whole effect depends upon the method of interlacing the warp and the weft in the process of weaving. Such cloths are made from yarns of every well-known kind of textile fibre. Designers of these fabrics must have an intimate knowledge of cloth structure, and should thoroughly understand how to make due allowance for the various restrictions imposed upon them by the particular type of loom in which the designs are to be developed. For such men a purely art training is not an absolute necessity, unless, indeed, when they are engaged in the preparation of the more elaborately figured kinds. Where coloured yarns are extensively used, as in the woollen, worsted, and silk industries, 3. Sound knowledge of the principles of colouring and their application to the blending of the fibres, and to the arrangement of the coloured yarns, is essential; while, for certain kinds of cloth, e.g., tapestries, brocades, etc., the designer is expected to be conversant with all branches — art, colour, weave structure, and processes of production.