What is Pigment Pigments are generally coloured, organic or inorganic solid

powder, and usually are insoluble. They are not affected physically or chemically in the substrate in which they are incorporated. Pigments can give a full range of colours. Pigments have a variety of applications that includes plastics, ink, and coating applications.

Difference Between Pigments and Dyes:

Points of Difference

Dyes Pigments

SolubilityThey are soluble Pigments are colourants that

are insoluble in water and most of the solvents

Number Available in Large numberComparatively lesser in number

Product resistance

Lower as compared to pigments

Very high

Lightfastness

Lower Dyes are very much vulnerable. Lights destroy colored objects by breaking open electronic bonding within the molecule

Traditionally pigments have been found to be more lightfast than dyes

Size

Dye molecules are comparatively smaller it's like comparing a football (pigment) to say a head of a pin (dye)

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 glass

Bonding Taking 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 method for

For example 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 carrier/binder

attaching the dye to the wood

Structure during the application process

During application process there is a temporary alteration in the structure of the dyes

During application, pigments have the capacity to retain particulate or crystalline structure

Imparting of Colours

Dyes can only impart colour by selective absorption of the dyes

Pigments impart colours by either scattering of light or by selective absorption

Combustible properties

Taking the example of a Candle making process, if the candles are dyed it is easily combustible and can be applied throughout the candle

In the example of a candle making as pigments are colored particles, they tend to clog a wick when burned. This makes them undesirable for a candle if it is colored throughout and used for burning

Chemical Composition

Usually the dyes are organic (i.e. carbon-based) compounds

While pigments are normally inorganic compounds, often involving heavy toxic metals

Longevity factor

The dye based printing inks do not last as long as the pigment inks

In case of ink based printing prints made with pigments lasts longer

Printing on substrates

Compatible with almost all the substrates that needs to be dyed

Owing to the physical makeup of the pigment inks the range for suitable substrates are limited

Colour gamutTaking the case of printing inks, dye based inks offers a wide variety

Prussian blue:

Dark blue, called the first of the modern pigments. It has very high tinting strength but is only fairly permanent to light and air.

It's an Iron-hexacyanoferrate accidentally formed while experimenting with the oxidation of iron.

It is an inorganic compound with the idealized formula Fe7(CN)18, containing also variable

amounts of water and other ions.

This dark blue solid is commonly abbreviated "PB." PB is a common pigment, the object of instructional experiments, and an antidote for certain kinds of heavy metal poisoning.

Because it is easily synthesized in impure form, it also has a complicated chemistry that has led to extensive speculation on its structure. It is used in paints and is the "blue" in blueprints.

Chemical Formula:

Uses

In Medical sciences:

How Prussian blue works Prussian blue traps radioactive cesium and thallium (mainly Tl-201) in the intestines and keeps them from being reabsorbed by the body. The radioactive materials then move through the intestines and are excreted (passed) in bowel movements. Prussian blue reduces the biological half-life of cesium from about 110 days to about 30 days. Prussian blue reduces the biological half-life of thallium from about 8 days to about 3 days.

Side effects of Prussian blue

The most common side effects of Prussian blue are upset stomach and constipation. These side effects can easily be treated with other medications. People may have blue feces (stool) during the time that they are taking Prussian blue.

Internal exposure to cesium or thalliumDoctors may also prescribe Prussian blue for use in treating people who have

been internally exposed to cesium or thallium. Internal exposure can happen through ingestion or inhalation, and it can be quite dangerous when not quickly treated.

The Prussian blue binds to these elements, preventing the body from absorbing them and expressing them quickly through the intestines to minimize exposure. Prussian blue should not be taken orally without the direction of a doctor, as it is very important to calculate an accurate dosage and to take a version which has been specifically designed for this use.

As a pigment: Pure Prussian blue is a very deep, rich blue. It can be mixed

with other pigments to create different shades, or used on its own.

Painters, woodcutters, and textile artists all work with Prussian blue, and it was also historically used to manufacture blueprints.

In laundry bluing: In laundry bluing, Prussian blue was historically added

in trace amounts to laundry water to make yellowed whites look more crisp. In microscopy, Prussian blue is often used as a stain to look for traces of iron,

By machinists and toolmakers: Prussian blue in oil paint is the traditional

material used for spotting metal surfaces such as surface plates and bearings for hand scraping.

A thin layer of non-drying paste is applied to a reference surface and transfers to the high spots of the workpiece. The toolmaker then scrapes, stones, or otherwise removes the high spots.

Prussian blue is preferable because it will not abrade the extremely precise reference surfaces as many ground pigments may.

References: http://www.dyespigments.com/what-pigment.html

http://www.dyespigments.com/what-is-dye.html

http://www.newton.dep.anl.gov/askasci/gen01/gen01703.htm

http://www.dyespigments.com/difference-pigments-dyes.html

http://www.absoluteastronomy.com/topics/Prussian_blue

http://en.wikipedia.org/wiki/Prussian_blue

http://www.colourindia.in/prussian-blue-pigment.htm

http://www.uh.edu/engines/epi2254.htm

http://www.essence-of-mineral-makeup.com/prussian-blue.html

http://www.wisegeek.com/what-is-prussian-blue.htm

http:// http://images.search.yahoo.com

http://painting.about.com/cs/colourtheory/a/prussianblue.htm

http://encausticpaints.com/Resources/QuestionAnswer/ PigmentWarningsPrussianBlueIsItSafe/tabid/566/Default.aspx

Class Notes