This is the oldest of fashion washes in denim after stone wash. The name acid wash is in reference to the acids used for this wash in old recipes. In new methods it is done with oxidation. Use of bleach/oxidative is very safe and economical in comparison to acids. Different chemicals are used and among them potassium permanganate (KMnO4) and sodium hypochlorite are mainly used.
Acid wash is typically done by soaking pumic stone in hypochlorite. Some time KMnO4 is used in replace of bleach. Selection of oxidant is very important and mainly depends on the type of fabric. When it is done with pumice stone the washer and garment should not contain any water. Dry garment is much suitable for this process then a damp one. Pumic stones are soaked in bleach and left it to open for little time so they get only damp rather than wet. Then they are processed in machine with garments. The extent of effect is controlled with process time, concentration of oxidant solution and quantitative ratio of garment to stone.
In some derivatives of this process cotton balls or cotton ribbons are used instead of pumic stone. The impact of cotton is very different form pumic stone. It produces more merged and cloudy effect. Cotton ball of cotton ribbon is more successful on damp rather dry garment. Again the concentration of oxidative solution, time of process and quantity of garments measures the effect. Cotton towels are some time used for this effect to produce more cloudy patterns on garment.
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Garment must be stone washed before going for acid wash. It is more prominent and uniform on medium stone wash than dark or light washes. KMnO4 cannot be used with cotton balls/ribbons. It is only possible with hypochlorite. Black sulfur is not process able with hypochlorite as sulfur reacts vigorously with sulfur and pace of process cannot be controlled.
One important thing about acid wash is that the process is without water so the effect will be more random and variation will to a larger extent than regular washes. So by keeping the batch size minimum this variation can be controlled. The simple relation is larger is the batch size greater is the variation in result
General Recipe Steps
- Stoning or/and Enzyming
- Soap Rinsing
- Acid Wash Process
- Softener Application
Stone/Cotton Ball Treatment
Stone/Cotton balls/Cotton ribbons are dipped in diluted solution of oxidant to make them ready for process. It is very important to remove the excessive quantity of solution from stones. This will be helpful in controlling the effects. This can be done by two ways. One is to let the soak out in open by placing them on mesh sheet and them running them in washer without water. When they get semi wet, they are ideal to use in process. This treatment is very useful for acid wash. Some time a quantity of raw stones or cotton balls is added to treat ones to control the intensity of pattern.