Absorption, diffusion, or bonding hold dye molecules to the fiber, with temperature and time being important determining variables. Acrylic fibers are coloured with basic dyes, whereas nylon and protein fibers like wool and silk are dyed with acid dyes and polyester yarn is dyed with dispersed dyes. The dye is absorbed by the fiber and becomes part of its structure.
The color comes from atoms in the dye that connect to atoms in the fiber. These connections can be broken if you wash the fabric too many times or use hot water. That's why colored clothes fade over time. There are several ways to prevent this fading: use colors that don't mix on the color wheel, only wear one color at a time, and choose fibers that aren't sensitive to heat or cold.
Silk and wool can't withstand very hot or cold temperatures so they must be washed and dried carefully or they might shrink or feel itchy. If you get hair stuck in your sweater's stitching, just pull it out - it'll be clean shaven sheep skin! Synthetic fibers are most often dyed with acid dyes which don't go through a washing process. They stay bright longer but will still fade over time due to light exposure.
There are two types of fiber dying processes: sublimation and absorption. In sublimation dyeing, the dye molecule decomposes into gases that leave behind empty space where the dye used to be.
Acid dyes, which are mostly used to color wool, silk, and nylon, and direct or substantive dyes, which have a high affinity for cellulose fibers, are examples of textile dyes. To give mordant dyes an affinity for the object being colored, chemical compounds such as salts must be added. The mordant may be applied before, during, or after dying. It is usually applied in large quantities and left to act on the fiber for some time.
The three main groups of dyes for coloring wool are acid dyes, basic dyes, and direct dyes. Acid dyes are generally considered more fast-drying than other dyes, while basic dyes are used when a deep shade is required. Direct dyes are used to add a specific color to a particular area of the fabric (for example, to create a pattern). They can also be called spot dyes because they only color a small part of the fiber at a time.
Wool is dyed using two methods: hot and cold. In both cases, the wool is first washed to remove any dirt or debris, then it is soaked in a vat containing a dye bath. The wool is immersed in the bath for a certain amount of time depending on the shade or depth of color desired. It is then rinsed in water and either hung to dry or washed again if it needs to be darker.
You're probably seeing a variety of yarn colors and sizes, but what about materials? The bulk of commercial yarn nowadays is synthetic acrylic yarn. Acrylic yarns are manufactured from acryonile, a polymer compound (a form of plastic). Natural yarn includes cotton, wool, and silk. All three are organic materials that are grown for their fibers rather than made synthetically.
Yarn gets its color from dyeing. When you buy a ball of yarn, it will be dyed one of two ways: either fully or partially. If it's fully dyed, that means all the fibers get treated with color; if it's partially dyed, some of the fibers get colored and others don't. For example, if you bought a red ball of yarn, some of the fibers would be red while others wouldn't. There are several reasons why manufacturers might choose to dye some of the fibers white when making yarn, such as improving the look of a solid color or adding flexibility to heavy fabrics.
Just like any other type of fiber, yarn can be contaminated with chemicals during production. These may include pesticides, dyes, and resinoids. Pesticides are chemicals used to kill insects that carry diseases; examples include DDT (dichloro diphenyl trichloroethane) and DDE (dichloro diphenyl dichloroethylene).