Vat dyes are water-insoluble dyes that can be converted to a water-soluble form through chemical reduction. They were first developed in the 1850s as synthetic dyes and include indigo dye. The vat dyeing process involves three steps - vatting to convert the dye to its soluble leuco form, oxidation to convert it back to insoluble form in the fiber, and after treatment. Vat dyes have high color fastness but more limited shades than other dyes and their application process is complex and time-consuming.

2. Topic
Vat Dyes

3. History
 Until 1850s, all dyes were obtained from naturals
sources, most commonly from vegetables, plants,
trees, and lichens with a few from insects
 Around 1900 Rene Bohn in GERMANY
accidently prepared a blue dye from ANTHRA scene,
which he named as INDIGO dye.
 After this, BOHN and his Coworkers synthesize many
other VAT DYES

4. Definition
 A water insoluble dye which is converted into a
soluble form by treated with a reducing agent in alkali
then reconverted into its insoluble form by
oxidation.

5.  The name Vat was derived from
the large wooden vessel from
which vat dyes were first applied
 Vat dyeing means dyeing in a
bucket and vat for coloration
textile products
 Almost any dye, including
fiber-reactive dyes, direct dyes,
and acid dyes can be used in a
vat dye
 The original vat dye is indigo
obtained from plant
Why They Called Vat Dyes?

6.  Redox reaction take place in this process
• Indigo is an example of this dye class, it changes from
yellow to green in the bath and then blue as the air hits it
• But not all vat dyeing is done with vat dye

7. GENERAL PROPERTIES OF VAT DYES
 Insoluble in water
 Can not be used directly for dyeing
 Can be converted to water soluble form
 Possess affinity to cellulosic fibers
 Involves two steps
 Reduction of vat dye into weakly Acidic Leuco form
 Salt formation by NaOH

10. CHEMICAL CLASSIFICATION

11. CLASSIFICATION OF VAT DYES
INDIgoid or Thio-INDIgoid Anthra Quinon Oid
 Low affinity for cellulose
 Low fastness properties
• Majority of vat dyes belongs
to this group
• Having a complex structure
• Posses high affinity
• Better fastness properties
than other two groups

12. STEPS IN VAT DYEING
A wide range of different techniques are used in
colouring processes with vat dyes .
All processes involve three steps: .
 Vatting .
 Oxidation .
 After treatment

13. Vatting
 Process of converting water insoluble form to water
soluble form known as vatting
 Sodium hydrosulphite is mostly used reducing agents with
NaOH

14. Oxidation
 After absorption by the fibre, the dye in its soluble
leuco form is converted to the original pigments by
oxidation
.
 This process is carried out in the course of wet
treatment (washing) by addition of oxidants
such as hydrogen peroxide

15. After treatment
 The final step consists in after treating the material in
weakly alkaline liqour with a detergent at boiling
temperature
 This soap treatment is not only aimed to remove
pigments particles, but also allows the crystallization
of amorphous dye particles, which give the material
the final shade and the fastness properties typical of
vat dyes

18. ADVANTAGES
 The vat dye have high color fastness, which is
uncommon in other dye classes
 The poor rubbing fastness
 inkodye is a type of vat dye that uses light rather than
oxygen to fix the dye
 Mostly used in garments industry

19. DISADVANTAGES
 Limited shade range (bright shade)
 Sensitive to abrasion
 Complicated application procedure
 Time consuming
 Slow process
 Not more suitable for wool