Suoravärit

Suoravärit, meaning "direct dyes" in Finnish, refers to a type of synthetic dye that can be applied directly to fabrics without the need for a mordant. This characteristic distinguishes them from many other dye classes that require a mordant, a substance that helps fix the dye to the fiber, making it more permanent and preventing it from washing out.

Direct dyes are generally anionic and are primarily used for dyeing cellulosic fibers such as cotton, linen, rayon, and sometimes silk. They achieve their substantivity, or affinity for the fiber, through a combination of hydrogen bonding and van der Waals forces. This allows the dye molecules to bind directly to the hydroxyl groups present in cellulose. The dyeing process typically involves dissolving the direct dye in hot water and immersing the fabric in the dyebath, often with the addition of an electrolyte like sodium chloride or sodium sulfate to promote dye exhaustion onto the fiber.

While direct dyes offer convenience due to their mordant-free application and bright shades, their colorfastness, particularly to washing, can vary. Some direct dyes may have moderate washfastness, while others can be prone to bleeding. They generally exhibit good lightfastness. The development of direct dyes in the late 19th century was a significant advancement in textile dyeing, making the process more accessible and efficient.