Post 447 -Gautam Shah
Fibres, yarns and fabrics have poor bulk, or have lost bulk during various treatments are re-bodied by many different substances. Bodying is also possible without any substantive coating. Certain heat and water treatments shrink the fabric, increasing the bulk.
Weighting or bodying is a fabric finishing process that may be applied at fiber, yarn or fabric stage. Users oriented bodying processes mostly occur after the fabric production, at clothes stage. One of the oldest known weighting materials has been the size. Starch, gums and gelatine have been used to size fabrics for stiffness, glaze and adding weight. Wool, jute, linen and such coarse fiber fabrics do not require weighting. Fabrics of cotton and silk, in fresh state, and used (after some wear) state need bodying.
Traditional sizing treatments are temporary. Modern day chemicals such as modified starch, polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), and acrylic co-polymers provide long-lasting effect. Sizing of the warp yarn is required to reduce breakage of the yarn during weaving.
Raw silk contains from 25 to 30 % of its weight in sericin or gum. When the fiber is cleaned or fabrics are washed, this substance is removed. Silks are weighted to recoup the loss in fiber weight, and to add greater body to fabric. Silk has an affinity for several metallic salts, like iron, lead, and tin. The weight lost in the de-gumming process is refurbished by soaking the fibre or fabric in a bath of the metallic salts. For freshly woven silk fabric, it is first placed in an acid solution of stannic chloride (a chloride of tin). After the absorption of the substance, the fabric is washed, placed into a solution of sodium phosphate and washed. During this process, an insoluble compound (tin phosphate) is formed. This adds weight and body. Sometimes further treatment with sodium silicate is done. A silk can hold considerably more than its own weight, though heavy weighting reduces abrasion resistance, leading to greater wear and tear. Weavers and merchants, once added 10 times more weight, then the customary processing loss of 20 %. One simple way to check presence of chemical weighting compounds is to burn a piece of silk fabric, and it leaves behind a perceptible skeleton of metallic compound.
Cotton and other materials are sized for very temporary to permanent treatments. This may be in the form of starch, gelatin, or resin or a combination of these with lubricating substances such as oils or wax. Starches and gelatin are temporary sizes and are removed during laundering. Cheap cotton or rayon fabrics are often heavily starched for stiffness which after laundering may become quite limp. Fabrics like organdy are permanently stiffened Cottons.
Wool fabrics are not weighted, but compacted or fulled to give the fabric more compact or denser structure. Melton cloth is very heavily fulled wool fabric, with a dense -felt like texture.