Just showing about Dyeing Classification.

1. Department of Textile Engineering
WPT I: CLASSIFICATION OF DYES & ABOUT VAT DYE.
TMF: BIO COMPONENT FIBER & CROSS SECTION VIEWS
OF ALL FIBER.
By
Supervisor:
Dr.Shah mohammad Fatah-ur-rahaman
Professor & Head
Sahadat Hossain
Contact Information:
Cell- 008801811365918
Email : sahadathossain1616@gmail.com

2. Presented by : MD SAHADAT HOSSAIN
PROGRAME: BSc. in textile Engineering
ID: BTX110300163

3. Vat dyes are an ancient class of dye, based on the
original natural dye, Indigo, which is now produced
synthetically, and its close chemical relative, historic
Tyrian Purple. Both cotton and wool, as well as other
fibers, can be dyed with vat dyes.
Not all vat dyeing is done with vat dyes!
"Vat dyeing" means dyeing in a bucket or vat. It can be
done whenever a solid even shade, the same color over
the entire garment, is wanted, using almost any dye,
including fiber reactive dye, direct dye, acid dye, etc.
The opposite of vat dyeing is direct dye application,
such as, for example, tie dyeing. "Vat dyes" are a
special class of dyes that work with a special chemistry.

4. Most vat dyes are less suitable than, say, fiber reactive dyes, for the
home dyer, as they are difficult to work with; they require a reducing
agent to solubilize them. The dye is soluble only in its reduced
(oxygen-free) form. The fiber is immersed repeatedly in this oxygen-
free dyebath, then exposed to the air, whereupon the water-soluble
reduced form changes color as oxygen turns it to the water-insoluble
form. Indigo is an example of this dye class; it changes from yellow,
in the dyebath, to green and then blue as the air hits it.
Instructions for dyeing with vat dyes
Vat dyes must be solubilized before use. They
are not soluble in their oxidized form. The
process requires the use of lye (sodium
hydroxide), which must be used with due
care, including the use of goggles.
Indigo is subject to major crocking (rubbing off of the dye onto other items)
unless it is applied carefully. This means use a weaker dyebath, and dipping
many times, rather than a single strong dipping. Indigo may be applied with
essentially the same recipes as other vat dyes, or it may be applied with
traditional fermenting baths, which are more finicky but which use easier-to-
acquire ingredients.

5. To solubilize vat dyes, use a mixture of sodium hydroxide (caustic
soda, or lye) and the reducing agent sodium dithionite (also known as
sodium hydrosulfite, and found in Rit Color Remover). Ann Milner's
recipe for dyeing 100 gram of fabric, in her Ashford Book of Dyeing,
calls for 5 grams of dye, 10 grams of sodium hydroxide, and 10 grams
of sodium hydrosulfite. The dye is pasted up with a small quantity of
water, as usual for any dye, then the lye is dissolved in cold water
and added, and the sodium hydrosulfite is sprinkled on top of the dye
mixture to dissolve it. Milner suggests using twice as much sodium
hydroxide and sodium hydrosulfite for blue or black vat dyes. The
fabric or yarn is covered with water and wetted out separately, and
then the dissolved dye is added. after fifteen minutes, the fabric is
removed from the dyebath, exposed to air to allow the dye to
oxidize, and then washed.

6. Online instructions: Aljo Dye, which sells a huge range of different vat dyes,
provides directions for the application of their Zymo-Fast Vat Dyes. PRO
Chemical & Dye, which sells some vat dyes, provides instructions online for
Immersion Dyeing using PRO Vat Dyes. Kraftkolour provides instructions for
using vat dyes in the form of a downloadable PDF document. Batik Oetoro
also supplies a page of online instructions for using vat dyes.

7. It's inconvenient to have to reduce your vat dyes in order to
dissolve them. However, it is impractical to sell the reduced
form of the dye, because it will oxidize in the air, back to
the insoluble form. The solution to this problem is for the
manufacturer to convert the soluble leuco acid form of the
dye to the leuco ester, such as by reacting the leuco acid
with sulfuric acid. The leuco form of this solubilized dye can
be regenerated by removing the ester group chemically
(with sodium nitrite in dilute sulfuric acid) or by the action
of light.
The drawbacks of solubilized leuco esters are their greater
expense and their poorer uptake into the fiber, which
results in paler shades. (This is explained in Wilfred
Ingamells' book, Colour for Textiles: A User's Handbook,
which is available from the Society of Dyers and Colourists
for £9.)

8. Vat dyes are, as a class, the most light-fast of all dyes.
However, not all individual vat dyes are equally resistant
to light. The following are light fastness ratings for the
unmixed vat dyes sold by one popular supplier:
Color name Color index
name
Light fastness
rating (out of 8)
VD01 Yellow vat yellow 5
VD02 Orange vat orange 2 5
VD03 Red vat red 13 7
VD04 Blue vat blue 6 7-8
VD08 Violet vat violet 1 6

9. A light fastness of 7 is excellent, but a light
fastness rating of 5 is no better than you'll find in
many other dye classes. (See Light fastness of
Different Types of Dyes.) Always ask your own
suppliers for light fastness ratings for their dyes,
as they may vary somewhat from these values.

10. The same reducing conditions which aid in fixing
vat dyes to the fiber also discharge many other
dyes. It is possible to exploit this by first dyeing
your fabric with a dischargeable dye of another
class (such as Remazol dyes, most Procion Mx
dyes, or many acid dyes), washing it out as usual,
then printing a discharge paste containing the
"illuminating" vat dye color. Granat
Favekompagniet, in Denmark, sells a range of vat
dyes especially selected for being suitable for this
purpose.