Vat Dyes’ Properties, Classification & Much More

Found amongst the oldest natural coloring substances used for textiles, the vat dyes offer first-rate fastness properties. They are so named because a vat (which means a bucket or a container) is used for the process of dyeing!
Although, other dyeing can also be done in a vat, but the term vat dyes specially describes the class of coloring substances that are applied to cellulosic fiber (fibers come from plants or plant based materials. For example, cotton) using a redox process.

Properties:
Here are some highlights of the common properties of Vat dye:

• Superior color fastness properties, which are exceptional in other dye classes
• Needs vatting for application
• Water insoluble dyes
• A number of colors can be produced
• Rubbing fastness is not good, but is can be easily lessened with special treatments to the fabric
• Especially used for cellulose fiber with PH (measure of hydrogen ion concentration) control.

Classification of Vat Dyes:
Depending upon the properties one popular classification of vat dyeing substances has been developed which is given below:

• The 1N (indanthrene normal)-group of dyeing temperatures of 600C. In such dyeing substances no salt is added to the dye bath because they have high portion of leuco dyes for cotton.
• The 1W (indanthrene Warm) - group of dyeing temperatures of 500C. In such dyeing substances some addition of salt is required so to aid exhaustion.
• The IK- group of dyeing substances requires low concentration of NaOH with dyeing temperature of 200C.

One special type of vat coloring agents is light-oxidized vat dyes that use light rather than oxygen in order to produce wide range of color effects along with color fastness. Elaborately, these coloring agents which are chemically similar to the vat coloring materials developed in light rather than dipping in the oxygen-free bath and exposing into the air. Dye itself attached to the fabric.

Dyeing Process:
Most coloring substances, which require a reducing agent (the element in a reduction-oxidation that transfers electrons to other chemical species such as atoms, molecules, ions etc.) for solubilization, are less suitable than fiber-reactive coloring materials. The coloring agent is soluble in its reduced (oxygen-free) form. The fiber is dipped again and again in this oxygen free dye bath and brings out in the air where the reduced form of water-soluble change the color as the exposing to oxygen turns it into the water-insoluble form.