The process uses large stones to roughen up the fabric being processed. The garments are placed in a large horizontal industrial clothes washer that is also filled with large stones. As the wash cylinder rotates, the cloth fibers are repeatedly pounded and beaten as the tumbling stones ride up the paddles inside the drum and fall back down onto the fabric.
A number of people and organizations have claimed to have invented stone-washing. According to Levi Strauss & Co., Donald Freeland, an employee of the Great Western Garment Company (later acquired by Levi's), invented "stone-washing" denim in the 1950s. Inventor Claude Blankiet has also been credited with having invented the technique in the 1970s. The jeans company Edwin claims to have invented the technique in the 1980s. It is commonly accepted that French stylists Marithé + François Girbaud are inventors of industrialization of stone washing ("Stonewash" technic).
Stonewashed jeans are jeans that have been treated to produce a faded, worn appearance. This is usually accomplished either by washing the jeans with pumice in a rotating drum, or also by using chemicals to create the appearance without the use of a rotating drum. The expanding cost of importing pumice stone from Italy, Greece and Turkey led to extensive mining of pumice deposits in California, Arizona, and New Mexico, triggering a negative response from American ecologist groups. The reduction of pumice usage and the growing disposal of its chemically-tainted residue triggered a search for novel methods, notably the use of alternative abrading materials or machines and the use of cellulase enzymes. Stonewashed jeans were a popular 1970s fashion trend, before commercial acid wash denim (discussed below) was introduced in the 1980s. In the 2000s, stonewashed jeans were heavily distressed, with pre-made holes, frayed edges and extensive fading caused by sandblasting.
Claude Blankiet with American Garment Finishers from Texas promoted the use of cellulase enzymes in the finishing industry. Cellulase was already used in the paper pulp, food processing industry and currently in the fermentation of biomass for biofuel production. Cellulase is produced primarily by fungi, bacteria and protozoan that catalyze the hydrolysis of cellulose. Since the enzyme decomposes cellulose fibers this enhanced the characteristic appearance that the jeans have been abraded with stones (and eliminated or considerably reduced the usage of natural pumice stones). Selecting the most suitable type of enzyme and their application for ageing jeans was the key to success. American Garment Finishers used a new cellulolytic agent patented in 1991 by Novo Nordisk from Denmark because of its safer effect on cotton fiber. Other finishers used an acid side Trichoderma fungi enzyme, cheaper and faster acting, but resulting in excessive fabric tear and a back lash because jeans pockets were lifting off.
Acid-washed denim (a misnomer since no acid is actually used in the process), is washed with pumice stones and chlorine until it is bleached almost white. California surfers and members of the 1960s counterculture prized Levi 501s and other jeans that had been bleached by the salt water due to their authentic, "lived in" appearance. As natural wear took weeks, or even months, it was not uncommon to hang a few new pairs of jeans to fade in the sun, then turn them over to fade the other side. For many surfers, this process simply took too long, so they sped up the process by soaking the jeans in diluted bleach and some beach sand. Simple chlorine bleach and muriatic acid were readily available at the time (and still are), as they were used to sterilize swimming pools.