Acidic dye is defined as a negatively charged dye, which contains one or more acidic groups, such as a sulfo group. A basic dye, on the other hand, is a positively charged stain that is usually synthetic and reacts with negatively charged particles.
According to Reference.com, acidic dyes are divided into three classes based on their fastness requirements, level dyeing properties and economy. The class also depends on the fiber to be colored and the dying process. Acidic dyes are best for dying protein fibers such as wool, alpaca and mohair. However, in addition to animal hair, acidic dyes also are effective for dyeing silk and synthetic fibers, such as nylon.
According to Kolorjet, a manufacturer of a range of dyes and pigments, basic dyes consist of amino groups and are usually aniline dyes. They are not water soluble but become water soluble after conversion into a salt. At a chemical level, basic dyes are positively charged and consist of cation function groups, such as -NR3+ and NR2+. Because of its positive charge, basic dyes react well with materials that are negatively charged, or anionic. Additionally, basic dyes are known for producing brilliant colors that are often referred to as basic stains.