Textile bleaching

Bleaching is then necessary to give the clean white appearance to the cloth. Cotton is ordinarily bleached by using a solution of cloride of lime.

Linen comes off the loom much darker than cotton and requires more time and care to bleach. Grass bleaching and chemical bleaching are used to produce the whiteness desired in this fabric.

A high-grade pure linen does not require a dressing finish for the natural finish is much finer than any artificial methods can produce. Lower grades are always starched to hide any defects in the cloth. Boiling out a sample will bring out the thin foundation weave if the cloth is of inferior grade.

The best method of bleaching wool white is by oxygen. Applications of sulphurous acid or sulphur dioxide gas do not ordinarily give a permanent bleach. When washing with soap, the natural color of the wool will return, or the white may turn yellow.

Silk bleaching is accomplished by first boiling off the gum in a soap solution. This gum is a natural thick oily substance coming off the cocoons. A great deal of the color of the unfinished silk is in the gum and upon boiling is readily removed in a soapy mixture. Either sulphur or hydrogen peroxide is used for further bleaching.

This boiling off of the gum naturally tends to reduce the weight of the silk which loss in weight is a problem to the manufacturer. To bring up this loss, he is tempted to weight the silk. This he does by adding a weighter in the dressing, usually salts of tin or iron. The action of these chemicals very often causes the threads to weaken and permits the cloth to split and crack along those weak fibres.

Salt water, perspiration, sunlight or moisture affect a silk that has been weighted.