Textile Dyeing Quiz: Dye Types, Fastness and Lab Dips

The right dye for each fibre

• Polyester: disperse dyes, usually at high temperature (around 130°C) under pressure in jet or HT dyeing machines. This is the main dyeing work in Surat's process houses.
• Cotton and viscose: reactive dyes, which form a chemical bond with cellulose and give bright, wash-fast colours.
• Silk, wool and nylon: acid dyes.
• Vat dyes, such as indigo, are made soluble for dyeing and then oxidised back in the fibre. Denim's blue is indigo.
• Blends such as poly-cotton need two dye classes, one for each fibre.

When the colour goes in

• Yarn-dyed: the yarn is dyed before weaving. Checks and stripes are usually yarn-dyed and look the same on both sides.
• Piece-dyed: the fabric is dyed after weaving, the most common method for solid colours.

Fastness

Colour fastness is how well a colour resists fading or bleeding in washing, light, rubbing and sweat. Rubbing fastness is also called crocking: whether colour rubs off onto other cloth or skin. Ask for fastness test results on large orders.

Natural dyes

Natural dyes include indigo (blue), madder (red), turmeric (yellow, but it fades quickly) and pomegranate rind. Most need a mordant, such as alum, to fix the colour to the fibre.

Approving colour: the lab dip

Before a bulk order is dyed, the process house dyes a small lab dip to match your shade. Approve it in daylight, then check the bulk against it. Shades still vary slightly between lots, so keep the dye lot in mind when reordering.