Colour Index

The chemical names of dyes can be very confusing and complicated. As a result of this, the practice of using names that are descriptive has arisen. Generally a dye is referred to by a simple name that is comprehended by people who is working with them. Which we can say as a common name. But the problem is that it is not uncommon for a dye to have names that are more than one. For example take basic fuchsin which was earlier known as magenta. Taking another example it is also quite possible that a same, or a nearly same name to be given to two different dyes. For example light green, has also been popularly used to refer to dye methyl green. Some of these names are historical or there can be cases where in order to sell a single compound different manufacturers gave different names, to avoid violating copyright or trademarks of each other.

What is a Colour Index?

Above cited specific reasons in the confusion for naming dyes, prompted a need for Colour Index. Let's first understand what a CI or Colour Index number is. It's basically a compendium of dyes, that has a huge volume of data. It was prepared in the UK by the Society of Dyers and Colourists. In the USA by the American Association of Textile Chemists and Colorists. It is available both in the book form, and on CD as well. In this reference book there is a very specific system to identify individual dyes. A five digit number is assigned to each individual chemical that is used as a dye. Consequently individual dyes get identified with reference to their CI number only. For example when specifying a dye for use in any staining method the CI number must be always provided.



To avoid any confusion regarding chemicals, in addition to the identification number or CI number, the colour index also has a system to assign a specific name (CI Name) for each of the dyes. The name given is totally based upon the dye's mode of behaviour, base colour and action. This is followed by a number. To give an example, the CI name given for chromoxane cyanine R (CI 43820) is Mordant Blue 3. Thus the CI name therefore gives a specific way to identify a dye. Although the CI name is used less often than the CI number, the CI name is as useful in identifying a dye for a particular staining method.

The following table ably illustrates the use of the Colour Index for yellow Organic pigment

C.I.Generic Name	C.I.Number	CAS Number	Colour
P.Y.17	21105	4541-49-1	Greenish Yellow
P.Y.74	11741	6358-31-2	Bright greenish yellow
P.Y.81	21127	22094-93-5	Lemon yellow shade

Features of the Colour Index

• Colorants get listed in the Colour Index strictly in accordance with the system of (a) Colour Index Generic Names (b) Colour Index Constitution Numbers.
  
  
• Detailed record of products that can be found in the market is put under a Colour Index reference. For each product name there is a listing of the manufacturer's name, principal usages, physical form, and comments to help the customers. This format has been devised after taking into confidence the coloration industry (including prominent manufacturers, users, CPMA and ETAD).
  
  
• Around 27,000 individual products are listed under a total of 13,000 Colour Index Generic Names.
  
  
• Popular format has been devised with an unique 'fingerprint' concept.
  
  
• Chemical structures that are depicted is strictly in accordance with the results obtained by modern researches on molecular conformation.
  
  
• Part 1 of the information gets freshly confirmed with suppliers and manufacturers. Part 2 of the information is either confirmed freshly with suppliers and manufacturers or is depicted as "carried over from the previous edition"

Application of Colour Index

Colour Index has a large number of users from a diverse range of industries. Some of them are the following:

• Colorant users, suppliers and manufacturers.
• Textile manufacturers.
• Paint manufacturers as well as suppliers.
• Manufacturers and suppliers of Plastics.
• Producers of Printing ink along with suppliers.
• Testing labs, Libraries, academic institutions.

Highlights of the Colour Index:

The following three tables highlights major information regarding the Colour Index

Part 1

• Part 1 Dye Groupings:
  • Acid
  • Mordant
  • Disperse
  • Natural Dyes and pigments
  • Food
  • Leather
  • Direct
  • Sulphur
  • Vat
  • Reactive
  • Ingrain Dyes
  • Azoic Diazo components
  • Azoic Coupling components
  • Oxidation Bases
  • Optical Brighteners
  • Intermediate Products
  • Reducing agents and Developers
• Each group of Dyes is subdivided into Violet, Blue, Green, Yellow, Orange, Red, Brown and Black

Part 2

• Structural formula(if known) of Dyes
• Manufacturing methods
• References(literature and patents)

Part 3

• Indexes:
  • Abbreviations of manufacturers' names
  • Commercial names
  • Generic names
• Colour Index is able to provide dye or pigment with 2 reference numbers on the criteria of a) Colouristic aspects b) Chemical classification:
  • The first one is the area of application and technique of colouration=>the C.I. Generic name.
  • The second technique is the one that is known as C.I. Constitution numbers.
• There is also provision of listing all the commercial names.