Indigo stones

Enzymatic stone-washing is performed either entirely without stones or sometimes by a combination of stones and enzymes. CeUulases are used to attack the surface of the cellulose fiber, but leave the interior intact. Denim garments are dyed with indigo blue, which stays on the surface of the yam. The ceUulase partiy hydrolyzes the surface of the fiber, and the indigo blue is partiy removed. Either neutral-type ceUulases acting at pH 6—8 or acid-type ceUulases acting at pH 4—5 are used for these processes. 

Cellulase enzymes break down the surface of the denim, thus releasing the indigo dye. The desired abrasion effect can be obtained totally without the use of purnice stones. 

Figure 6.2 Effect of cellulase on indigo dye on denim cloth stone-washing.

Stone blue is Hsted as a synonym for indigo q.v.) by Schweppe (1997). 

The principal dyes used by medieval dyers were indigo from woad for blue, alizarin and purpurin from madder for red, and luteolin from weld or cro-cetin from saffron for yellow some had been used long before the Middle Ages and weld was known in the Stone Age. Organic pigments have also been used on manuscripts, notably saffron, weld, indigo, woad, Tyrian purple, madder and carmine. 

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