Hexaplex trunculus degrades, resulting in blue only. Nonetheless, archeologists have confirmed Hexaplex trunculus as the species used to create the purple-blue dye; large numbers of shells were recovered from inside ancient live-storage chambers that were used for harvesting. Apparently, 10- to 12,000 murex yielded only one gram of dye. Because of this, the dye was highly prized. Also known as "Royal Purple", it was prohibitively expensive and was only used by the highest ranking aristocracy. A similar dye, "Tyrian purple", which is purple-red in color, was made from a related species of marine snail, "Murex brandaris". This dye (alternatively known as "imperial
Sulfur dye rubbing. The dyes are bleached by hypochlorite bleach. Due to the highly polluting nature of the dye-bath effluent, sulfur dyes are being slowly phased out in the West but they are used on a large scale in China. Recent advances in dyeing technologies have allowed the substitution of toxic sulfide reducing agents. Glucose in basic solution is now used and both low sulfide and zero sulfide products are available. Future developments in the field of reducing dye levels by means of electro-chemical processes are promising. Sulfur dye Sulfur dyes are the most commonly used dyes manufactured for cotton in terms