Originally, heavy woven cotton denim was sold in one shade: indigo blue. Indigo dye provided a rich depth of color and durability, as denim clothing was predominantly worn by hard-working farmers, slaves and gold miners, all of whom needed clothing that didn't need frequent washing and wouldn't wear out easily.
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Still valued for its durability, denim now projects an ever-changing fashion statement by featuring a wide array of shades, colors, finishes and textures.
Various bleaches applied to denim leave it with a soft light blue color. Sometimes workers apply the bleach unevenly during the process, to result in a light and dark blue mottled appearance on the finished fabric. Very heavy bleaching results in an almost white shade of denim.
Denim tumbled in a washing machine with pumice or synthetic stones results in a vintage or used appearance in the final garment. Stone-washed denim can end up light or dark in color, depending on the texture of the stones used in the process and the total length of time the material was abraded by the stones.
First utilized in the 1980s, this chemical process strips denim of its dye through washing with stones soaked in sodium hypochlorite or another acidic substance. This process results in a mottled, bleached appearance, often resembling marble. Sometimes acid-washed denim has a yellowish cast as the result of the acid not being fully neutralized at the end of the washing process.
Soft shades of faded blue denim result from ozone or water jet fading procedures. Workers dissolve ozone into water in a washing machine before adding the denim, or they subject it to ozone gases in a special fading chamber. With water jet fading, strong jets of water remove color gradually until the fabric becomes the desired shade of blue. These non-chemical procedures cause little damage to the fabric.
Over-dyed or tinted denim fabrics have usually been stone washed to remove some of the blue dye from the surface of the fibers. After the garment is sewn, workers apply another shade of dye, often by hand using sponges or paintbrushes. Most often, they apply colors in the brown or yellow range, but occasionally other colors are used. The garment goes through another washing process, resulting in subtle color variations in the finished product.
After stone washing the denim, the manufacturer treats the material with special chemicals. These leave a brown or gray cast that only appears in the areas exposed to the chemicals. This results in a dirty appearance, as though the wearer had stained the garment in spots while gardening or otherwise working in the dirt.