Until late 70s, denims were mainly dyed with pure Indigo. Bottoming, with sulphur black or Hydron blue dyes, was then introduced to partly replace the expensive Indigo dye. Later, bottoming was adopted to produce Super-dark (or double-dip) denim. In mid-2010s, sulphur black bottoming was used to produce the so-called "Black-Blue denim". Topping was introduced to the market around the same time as bottoming. Initially, topping was done in the si2ing box using direct dyes. Later, in the mid-2000s, topping technique was extended to produce the so-called "Blue-Black denim" (Indigo topped with sulphur black) and "Black-on-Black denim" (sulphur black topped with direct black). In late 80s, tinting (with direct red dyes) was applied to pure Indigo denim to imitate the shade of bromo-Indigo dyed denim from Japan. Then, in rnid-90s, "Vintage look" has gained market acceptance for which dyers use direct dyes (e.g. yellow, brown, black, etc.) to tint abraded (e.g. stone wash) denim for a worn-out effect.
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