Acid dyes are generally divided into three classes according to their fastness requirements, migration ability, and dyeing pH. Acid dyes affix to fibers by hydrogen bonding, Van der Waals forces and ionic bonding. While some acid dyes work in water, many choose to activate dyes in acid dye-baths instead. According to the Bronsted–Lowry acid–base theory, an acid is a molecule or ion capable of donating a proton, and this is determined by the acid dissociation constant.

Fibres

In the laboratory, home, or art studio, the acid used in the dye-bath is often vinegar (acetic acid) or citric acid. The uptake rate of the dye is controlled with the use of sodium chloride. In textiles, acid dyes are effective on protein fibers, i.e. animal hair fibers like wool, alpaca, and mohair. They are also effective on silk. They are effective in dyeing the synthetic fiber nylon, but of minimum interest in dyeing any other synthetic fibers.

Histology

In staining during microscopic examination for diagnosis or research, acid dyes are used to color basic tissue proteins. In contrast, basic dyes are used to stain cell nuclei and some other acidic components of tissues.

Food Industry

Acid dyes can also be used as food colouring, helping to increase the attractiveness of certain foods, and thus becoming more appealing to customers. Some examples include erythrosine, tartrazine, sunset yellow and allura red, to name a few, many of which are azo dyes.

# Name Shade
1 ACID MIXTURE
2 ACID YELLOW 110
3 ACID RED 119
4 ACID RED 57
5 ACID GREEN 25
6 ACID GREEN 16
7 ACID BLUE 114
8 ACID YELLOW 194
9 ACID ORANGE 67
10 ACID ORANGE 74
11 ACID ORANGE 116
12 ACID BLACK 194
13 ACID BLACK 172
14 ACID BLACK MIXTURE
15 ACID RED 183
16 ACID RED 195
17 ACID RED 186
18 ACID YELLOW 114