acid-wash
To treat (a material) with bleach so as to mottle or discolor it.
acid-wash: bleach treatment that creates mottled, faded effects
Acid-washing is a chemical treatment applied to dyed fabrics, most commonly denim, to create a deliberately worn, faded, or mottled appearance. The process uses chlorine bleach or potassium permanganate to selectively remove or lighten dyes from the fiber surface, producing irregular patches of color loss. The result ranges from overall pale discoloration to dramatic high-contrast spotting, depending on application method and concentration.
In denim production, acid-washing emerged as a cost-effective alternative to traditional stone-washing in the 1980s. Instead of tumbling garments with pumice stone to achieve a faded look, workers spray or soak finished fabric in dilute bleach solution. The treatment is faster and requires less mechanical wear on machinery and fiber. A typical bath might contain 2 to 5 percent available chlorine, applied at temperatures around 40 to 60 degrees Celsius for 10 to 30 minutes.
The mottled effect results from uneven bleach contact on the fabric surface. When garments are bunched, folded, or sprayed rather than fully submerged, the bleach reaches some areas while others remain protected. The severity of color removal depends on fiber type, dye chemistry, bleach concentration, and contact time. Dark indigo denims bleach to pale blue or white; colored fabrics may shift hue entirely as selective dye molecules are destroyed.
Practical hazards and control
Acid-washing presents significant occupational and environmental concerns. Chlorine gas can be released during handling, especially if the bleach solution contacts residual acidity in fabric or water. Proper ventilation is essential. The spent bleach baths are corrosive and must be neutralized before disposal. Workers must wear appropriate personal protection including gloves, eye protection, and respiratory equipment when bleach concentrations are high or ventilation is limited.
The term "acid-wash" is somewhat misleading. Traditional chlorine bleaching is not truly acidic; however, some processors use dilute hydrochloric or sulfuric acid to enhance the effect or adjust pH after bleaching. This dual-chemical approach can intensify mottling but adds complexity and cost. The name persists from early marketing language that emphasized the aggressive chemical action rather than distinguishing chlorine from acid-based processes.