This is the most common and basic process for producing a washed-down look on denim garments. Towards the end of the seventies, pumice stones were discovered to accelerate the aging process of indigo dyed denim garments.
The stones in widespread use today are pumice stones, which have numerous pores. These pores have very sharp edges, facilitating a very high degree of abrasion.
A typical stone wash process is as follow:
The degree of color fading and change of garment feel depends very much on the ratio of weight of the stone to the fabric weight, which can vary from 0.5:1 to 3:1. During the treatment, the outer most layer of the indigo-dyed yarn is partially separated and the portion of the fiber inside, which is undyed, comes to the surface. The surface gets a softer handle through the mechanical process with pumice stones.
The degree of the wash-down effect depends upon several factors – the size of the stone, stone ratio, liquor ratio, duration of treatment, garment load, etc.
The size of pumice stones available for stone washing vary from 1 cm to 7 cm in diameter. Pumice stones, around 2 to 3 cm in diameter, are used for finer denim qualities. The common size employed for normal denim qualities is 3 to 6 cm in diameter.
Different wash names like sand wash, golf ball wash, micro wash and micro-sand wash — which are types of stone wash — refer to the use of very small size pumice stones.
Drum washing machines are used for stone washing. The capacity of drum washing machines can be up to 200 kg. Some of these machines are equipped with tilting facility to empty the washed garments.