Acid dyes are used to dye protein fibers such as wool, angora, cashmere, and silk, as well the milk protein fiber called Silk Latte, the soy protein fiber called Soy Silk, and the synthetic polyamide fiber nylon.
Acid dyes sound scary to some novices, who imagine that
the dyes themselves are caustic strong acids. In fact, the dyes are
non-caustic, are in some cases non-toxic, and are named for the mild acid (such
as vinegar) used in the dyeing process, and for the types of bonds they form to
the fiber. Some of them are significantly more toxic than
fiber reactive dyes, while others are even safe enough to
eat, and are sold as food coloring.
According to Linda Knutson's Synthetic Dyes for Natural Fibers, acid dyes fall into several classes: 1, leveling
acid or strong acid dye, 2, milling or weak acid dyes, and
3, super milling or fast acid or neutral
acid dyes. Leveling Acid Dyes have been sold under the trade names of
Kiton, Erio, Intracid, Sandolan, and Amacid, among others; they are also the
acid dye component of all-purpose or union dyes such as Rit and Tintex,
says Knutson. It's difficult now to find out which specific acid dyes
fall into which of these dye classes, however. At least part
of the reason is that the information is not always useful to
Levelling Acid Dyes (Kiton Dyes)
Levelling Acid dyes (or Acid Levelling dyes), also known as Strong Acid dyes or Equalizing dyes, are a class of acid dyes that produce a very even, single-color solid effect. The trade-off is that items dyed with Leveling Acid dyes should not be machine washed or washed in warm water; they should be dry-cleaned or hand-washed in cool water. For more information, see the page Levelling Acid Dyes (Kiton type Dyes).
Wash Fast Acid Dyes
Wash Fast Acid Dyes are a reasonably priced collection of
many different and worthwhile acid dyes, sold by PRO Chemical & Dye,
including dyes referred to in some books as the "Nylomine" dyes.
The name "Wash Fast" is a bit of a misnomer, as some of the
dyes in the group are not very washfast at all, but this dye
series has a very devoted following. See Which washfast acid
dye colors are pure, rather than mixtures? for a
complete listing of the pure dyes sold by ProChem. For a
table showing the washfastness and lightfastness ratings for
many of these dyes, as well as other dyes, see What is lightfastness?.
Jacquard Acid Dyes
Jacquard's acid dyes are similar to ProChem's Washfast Acid dyes; some dyes are the same in both lines, while many others are completely different, though of similar colors. Jacquard gives instructions online for the use of these dyes, as well as lightfastness and washfastness data (which can also be seen on this site in the acid dyes table section of the What is lightfastness? page).
Lanaset Dyes are a very beautiful range of dyes for wool that are notable for their high degree of washfastness. Lanaset Dyes include both 1:2 premetalized acid dyes and special fiber reactive dyes that react with wool under acid conditions. They have been selected to work well together. For more information see the page About Lanaset dyes, as well as "Which Lanaset dye colors are pure, rather than mixtures?".
One Shot Dyes
Shot Dyes are a form of acid dye, developed by
PRO Chemical & Dye. They are
also sold under the name of Country Classic Dyes. They are
very convenient to use, as all dye auxiliaries are included
in the dye mixture; all you need to add are your fiber, plus
water and heat. However, the convenience increases the cost
somewhat. More provblematically, no information is available as to which
acid dyes may be represented in this series.
All purpose dyes
All purpose dyes can be used to dye protein fibers, because they include an acid dye in their mixture (probably Levelling Acid dyes). See the page All Purpose Dyes. Unlike cottons, protein fibers will do best with the addition of a mild acid such as vinegar or citric acid to the dyebath.