Already more than 20 years ago appeared a procedure to make a stonewash garment looking more authentic. In that time it was just Potassium Permanganate applied by spray on washed garments.
Nowadays laundries still use this technology but in most finishes a scraping is done on rigid garments before wash and spray them. Doing like this the look is much more authentic. With different concentrations of the Potassium Permanganate and different amount of sprayed solutions, more or less white effects appear on the sprayed zone. The first chemical reaction between Potassium Permanganate and the blue Indigo is an Oxidation of the dyestuff and as a result remains brown Manganese dioxide on the pants. This needs to be washed out, usually done with Bi-Sulfite and a warm bath.
To obtain an even higher contrast then above described itís necessary to apply the Potassium Permanganate by brushing or sponging. Therefor you use different brushes or sponges and apply manually the adjusted Potassium Permanganate solution, just move over the desired areas with the brush or sponge. Afterwards neutralize as usually.
Itís of course also possible to use Hypochlorite instead of Potassium Permanganate solution. Depending on the fabric it gives a different look. The difficulty in using Hypochlorite is, that you cannot see well where you applied Hypo and that you donít know when the bleaching effect of Hypo is finished. Thatís why in many cases itís useful to put some few grams Potassium Permanganate into the Hypo solution. To stop the bleaching action of the Hypo in time you should have a big barrel with water and Bi-sulfite close to the apply-area. Afterwards neutralize as usually.
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