Both dyes and pigments appear to be coloured since they absorb several wavelengths of light preferentially. In contrast through a dye, a pigment usually is insoluble, and has no affinity for the substrate. Though, there has been an interchange of usage between the 2. Pigment dyeing is a reasonably recent addition.
Definition of Dyes
A dye can generally be explained as a coloured material that has an affinity for the substrate to which it is being applied. The dye is usually applied in an aqueous solution, and might need a mordant to develop the fastness of the dye on the fiber.
Features of Dyes
At the extremely basic level, utilize of colour in identifying individual components of tissue sections can be completed primarily through dyes. Even though there are other means, Dyes are though, the largest group that can simply be manipulated to our liking. Dyes are applied to several substrates for instance to textiles, leather, plastic and paper in liquid form. One trait of dye is that the dyes must get totally or at least partially soluble in what it is being put to. The rule that we pertain to other chemicals is similarly applicable to dyes also. For example, certain dyes can be toxic, carcinogenic or mutagenic and can be hazardous to health.
How Can the Colour of the Dyes be Altered
The answer lies in the modifiers. Colour modifiers as methyl or ethyl groups can in fact alter the colour of dyes. They do so via altering the energy in the delocalised electrons. It has been found that through addition of a particular modifier there is a progressive alteration of colour. An instance can be known for methyl violet series.
The subsequent step describes what occurs to the colour of the dyes when modifiers are added
Step A: When no methyl group is added, the original dye Pararosanil as it is termed is red in colour.
Step B: As 4 methyl groups are added ruddy purple dye Methyl Violet is got.
Step C: Through the addition of more methyl groups a purple blue dye Crystal Violet is obtained. It has in it 6 such groups.
Step D: Further addition of a 7th methyl group the dye that is got is termed Methyl green.
What Gives Dyes Solubility and Cohesiveness?
The answer to this riddle lies in substance termed Auxochrome. Auxochromes have the ability to intensify colours. It is a group of atoms that attaches to non-ionizing compounds yet has to ionize. Auxochromes are of 2 kinds, positively charged or negatively charged.
Dyeing and Fabric
This is an application of dyes by respect to the fabrics.
Table: Kinds of Dyes and Fabric
Cotton, cellulosic and blended fibres
Cotton, cellulosic fibre
Cotton, cellulosic, blended fabric, paper
Cellulosic fibre and fabric
Wool, silk, paper, synthetic fibres, leather
Printing Inks and Pigments
Silk, wool, cotton
Conventional pigment dyeing system
There is a challenge in pigment dyeing. In the procedure of pigment dyeing no real chemical reaction occurs between the dye and the fabric. In its place, what happens is that the pigments get seated on the fabric through the assist of binders.
Pigments aren't soluble in water and show no affinity for fibre. So, conventional dyestuff-based dyeing conditions aren't feasible for pigment dyeing. To come to terms through these limitations, a new type of pigments have been formulated for utilize in fibres. Such are continued in a stable dispersion in the medium of water via anionic surfactants. This kind of pigment is recognized as pigment resin color (PRC), primarily utilized in printing. Several of the popular pigments utilized in fabrics are specified here.
a. Yellow colour: Acetoacetic acid anilide pigments
b. Red: Azoic pigments
c. Blue or green: Phthalocyanine pigments
A typical procedure of pigment dyeing for cellulosic textile substances consists of padding the textile materials through a dye bath. The dye bath encloses anionic or neutral colour dispersions of pigments. Along by the pigments it as well contains anionic binders, acid-liberating catalyst, anti-migrating agents, and other kinds of additives. Then, the textile materials are dried at high temperatures, this cures the film-forming binders and pigment colours resolutely on the textiles.
Differences between Dyes and Pigments
The main dissimilarities between the Dyes and Pigments are highlighted below
Table: Differences between Dyes and Pigments
Points of Difference
They are soluble
Pigments are colourants that
are insoluble in water and
Available in large number
Comparatively lesser in
Lower as compared to
Lower Dyes are very much
vulnerable. Lights destroy
coloured objects by
breaking open electronic
bonding within the
Traditionally pigments have been found to be more lightfast than dyes
Dye molecules are
comparatively smaller it's
like comparing a football
(pigment) to say a head of a
Pigment particles are about
1-2 microns in size. (1
micron =1/1000 meter). It
means that the particles can
be seen under a magnifying
aking the example of
dyeing a wood surface, the
dye and the substrate
(wood) that is dyed are
chemicals that have certain
features called functional
groups. At the level of
molecules these groups
serve as open pockets of
electrostatic charges (+ or -
). The functional group in
dyes, serve as a point for
attaching the dye to the wood
Taking the example of a
wood surface pigment
requires the help of a binder
for gluing. As it is an inert
substance which is merely
suspended in a
Structure during the
During application process
there is a temporary
alteration in the structure of
pigments have the capacity
to retain its particulate or
Imparting of Colours
Dyes can only impart colour
by selective absorption
Pigments impart colours by
either scattering of light or
candle making process, if
the candles are dyed it is
easily combustible and can
be applied throughout the
In the example of a candle making as pigments are coloured particles, they tend to clog a wick when burned. this makes them undesirable for a candle if it is coloured throughout and used for burning
Usually the dyes are organic
While pigments are
compounds, often involving
heavy toxic metals
The dye based printing inks
do not last as long as the
In case of link based printing prints made with pigments last longer
Printing on substrates
Compatible with almost all
the substrates that needs to
Owing to the physical
makeup of the pigment inks
the range for suitable
substrates are limited
Taking the case of printing
inks, dye based inks offers a
As compared to dye-based inks, pigment inksets somewhat lags behind, on the same paper stock
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