The International Colour Index Marks 100 Year Anniversary

February, 2024

It is impossible to give precise dates of when the Colour Index begun life, rather it evolved.  However, we can be precise about when it was first published and that is exactly 100 years ago in 1924.

Early attempts to classify dyes:  The history of the Colour Index goes back much further into the earliest days of synthetic colour.  Dyers needed to distinguish between the various classes of dyes to determine whether they were suitable for their fibres and application conditions. A dictionary was published in 1870 by J.W. Slater, entitled “The Manual of Colours and Dyeware”.  In 1885, “A Classification of Coal-tar Dyes” was published by R. Benedikt and E. Knecht detailing commercial names, structures and properties, but this was largely a translation of  an earlier publication in German by Benedikt.  E. Knecht was the editor of the Journal of the Society of Dyers and colourists and Head of the Department of Chemistry at Bradford Technical College.

Probably the most comprehensive and authoritative publication appeared in 1888 in the form of a booklet in German entitled “Tabellerische Übersichte der im Handelbefind-Lichenkünstlichen Organischen Farbstoffe”  (Tabular Survey of Synthetic Organic Colouring Matter) edited by G. Schultz and P JuliusIt was published to celebrate the birthday of Professor A.W. Hofmann, who arrived from Germany to become the first director of the Royal College of Chemistry in London, and whose name is synonymous with dyes as well as being the supervisor of W.H. Perkin, who discovered the first synthetic dye - Mauve in 1856.  The tabular nature of this publication proved very popular as a reference document, with dyes being listed under the headings:

  • Scientific name
  • Empirical formula
  • Constitutional formula
  • Method of preparation
  • Year of discovery, references
  • Properties and application details.

While the first edition had 278 entries, the seventh edition contained 1471 entries. All seven editions (including supplements) were published between 1888 and 1939.

An English translation of the second edition of this publication was published in 1894.  It was translated by A.G. Green, then the chief chemist at Clayton Aniline but who was later to become the Professor of Tinctorial Chemistry at the University of Leeds. However, he made many additions and took advantage of it being in English, aimed at the UK and American markets.

In 1921 the Society took the decision to produce an authoritative publication, detailing the commercial name of dyes, their chemical structure and application class.  This resulted in the first edition of the Colour Index when it was published in 1924. This publication quickly established itself as the international standard, helped by its use of the English language.  This publication was designated “Systematic Survey of Organic Colouring Matter”.   In 1904 a second edition was published, but included many natural dyes and structures were revised to conform to the quinonoid theory of colour.  Of the 454 colorants that were included in the first edition, 59 had become obsolete but 300 additional colorants added plus the 16 natural colorants.

First Edition:   Although Green had intended to prepare a revised edition, it was never published. Meanwhile in 1921 Society of Dyers and Colourists took the decision to publish a book that would provide the constitution and properties of a comprehensive range of colorants used in the dyeing, printing and paint industries.  Dr F.M Rowe was appointed the first editor and it was decided to publish the “Colour Index” in parts.  It turned out to be a much larger project than anyone had anticipated, so it was not until 1922 that the first of twelve parts were issued, covering over 100 colorants, based on those containing monoazo, nitroso, and nitro groups.  Further parts were published monthly and the work completed at the end of 1923.  These editions were bound and published as the First Edition of the Colour Index in January 1924.The total cost was around £5,500 and the Society was widely praised for embarking on such an ambitious project.  Dr Rowe became the Professor of Colour Chemistry and Dyeing at the University of Leeds in 1926.

The format of this First Edition was not dissimilar from te Schultz and Julius publication, using the chemical constitution and spectral hue.  It was divided into three sections:

  1. Synthetic organic dyes (1 – 1230)
  2. Natural organic dyes (1231 – 1254)
  3. Natural and synthetic inorganic colouring matter (1256 – 1316).

Each colorant provided the following information:

  • Index number (the Schultz number from the 5th and 6th editions was also included.
  • Commercial name and the manufacturer
  • Constitution, and components
  • Preparations
  • Discover and associated literature.
  • Properties, application matters

Although there was always an intention to give each product a name, no system could be found which would satisfy the majority of stakeholders.

This first edition of the Colour Index did not meet with universal approval, especially in Germany.  Dr Schultz claimed it infringed his copyright.  It was agreed that the Colour Index had relied heavily on Dr Schultz’s work and the Society made a grant of £250 towards Dr Schultz.  Although not altogether satisfying some aggrieved parties, no legal action was forthcoming and an out of court settlement was reached.

The Index was quickly accepted as a definitive work in English.  However, it quickly became out of date and a supplement was published in 1928, especially concerning product names.  Good sales continued until the early 1940s, when copies had to be reproduced in 1948 and 1951, but by 1954 sales ceased.

Second Edition:  Work on the second edition had already started in 1943, with the involvement of the American Association of Textile Chemists and Colorists and an editorial partnership was agreed.  There was still a shortage of paper of the required quality in the UK, but the Americans were able to provide the Society with such paper.   Volume 1 of the second edition of the Colour Index was finally published in December 1956, significantly just one hundred years after Perkin had discovered Mauve. Volumes 2 and 3 followed a year later and volume 4 in 1958.   A total production budget cost of £90,000 had been set, and to everyone’s credit it was completed within this budget.

The second edition made no claim to just being an updated version of the First Edition.  It comprised of three parts:

Part l:  (Volumes 1 and 2, Technology and commerce) Classification of dyes and pigments according to usage, in spectral order from yellow to green, plus achromatic hues.

This introduced the CI Generic name, which has proved a great asset to the Colour Index and has been adopted by many statutory and international organisations, including all trade statistics.  The Generic name (e.g. CI Acid Blue 9) proved very popular,  as it allowed both commercial and technical sides of the coloration industry to talk about dyes and pigments, without having to use any single manufacturer’s nomenclature.  Some professional associations insist that articles in their publications or lectures given as part of their technical programme, have to be done without using commercial names.  It also had an impact by offering the commercial and technical arms of the coloration industry the opportunity to talk about pigments and dyes without resorting to competitors’ trade names.

It is much easier to remember a Generic Name such as CI Acid Blue 9, than to use the

  • Chemical Constitution: (disodium;2-[[4-[ethyl-[(3-sulfonatophenyl)methyl]amino]phenyl]-[4-[ethyl-[(3-sulfonatophenyl)methyl]azaniumylidene]cyclohexa-2,5-dien-1-ylidene]methyl]benzenesulfonate
  • CAS numbers:  3844-45-9
  • EU references:   E133

The Colour Index Generic Name (CIGN) is issued to a specific application group on a chronological basis, so it gives no indication of the colorant’s chemical nature. Colorants were given a 5 figure constitution numbers, and when started numbers ended in either 0 or 5 leaving gaps for new introduction.

Part ll:  (Volume 3, Chemical Constitutions)

This part of the Index gives the chemical constitution of the colorant, and many intermediates, where these are known.  The number is clearly defined in sections and there is a logical sequence following precise rules, so that similar constitutions will have similar numbers.  The numbers had 5 digits.

CI Acid Blue 9 has the Colour Index Constitution Number (CICN) -  CI 42090.

This part of the Colour Index also gave information where known, on how the colorant was manufactured, who invented the product and any literature references such as British Standards, BIOS and FIAT information.

Part lll:   (Volume 4, commercial names)

This part of the Colour Index consisted of an alphabetic list of commercial names giving the manufacturer, CI Generic Name and the CI Constitutional Number.

This always proved to be the most difficult to keep up to date as commercial names changed.  This was recognised by the regular publication of “Additions and Amendments” from 1958.  This second edition contained approximately 31,500 entries.

Third Edition:

Shortly after the introduction of the second edition, industry discovered and introduced Reactive dyes, requiring a supplement to be published in 1963, but the impact was such that a new edition was required and in 1971 the Third edition was introduced. This edition set new standards, but in some way its success also caused problems. The CI started to be used by people outside the industry.  UN tariff codes for dyes and pigments are mainly based on CI numbers.  US import statistics are classified by CI numbers. While not in itself a problem, this led to the development of new colorants with relatively minor alterations, in order to get a new CI numbers that enabled products to be imported at lower rate of duty.

More problematic is the use of CI references in specifications.  As the CI number applies only to the essential colorant and does not give any purity, toxicity or performance specification, there are limits to designations being used in specifications. CI names have been used for positive lists for food packaging, cosmetic ingredients and even for the dyes used to distinguish the lesser taxed gas oil and agricultural diesel from transport diesel, without any consultation with the Society about the essential nature of the CI.

It was recognised, especially for pigments, that including fastness data in the Colour Index was not appropriate.  Colorants with an identical constitution can have different fastness properties dependent on how the are applied, on their substrate and in the case of pigments on the crystal modification and particle size distribution.

The wider use of the CI also led the larger European dye manufacturers to believe the CI gave legitimacy to inferior products made by less experienced manufacturers. Several traditional manufacturers ceased to apply for CI registrations for their newly developed products.

Designating Chemical Constitution Numbers:

The knowledge required to know how to designate a product with a Constitution Number in the Colour Index has become very technical and we have been very fortunate to have the services of  Dr Geoff Hallas, who as an independent academic sometimes needs to see those chemical constitutions which are given to us in confidence.  Keeping up the tradition, Dr Hallas was a senior member of staff from the Department of Colour Chemistry & Dyeing at the University of Leeds.  The requirement for those registering a new product to disclose the precise chemical nature became necessary when it was discovered that certain identical colorants had been given different CI Generic names as they had been unwittingly registered in confidence by more than one manufacturer.  There was therefore no way one could ensure the CIGN did not have a duplicate registration.  Manufacturers can now give their structures in confidence to ensure there can no longer be a possibility of the same chemical entity being given two different CICN numbers.

Pigment and Solvent Dye edition (1997):

Meanwhile manufacturers of pigments and solvent dyes (P&SD) cooperated to build on the Pigments and Solvent Dyes version published in 1982, to redesign the format, removing the references to the technical data.   However, manufacturers do have an opportunity to characterise their commercial product by having adding a few words to characterise their product for chemically identical products.

Web version:  

The rapid changes that have taken place in the coloration industry has made keeping printed data up to date.  It was realised several years ago that this could only be achieved by moving the Colour Index onto the web.  This allows changes to be made much quicker and instead of having big thick volumes, those who have purchased a subscription now have access to the Colour Index or parts of it as appropriate.

The responsibility for compiling information and marketing it has moved from the Society of Dyers and Colourists to their trading subsidiary SDC Enterprises.

The editorial board for pigments and solvent dyes is truly international, with a very good partnership with the Color Pigment Manufacturers Association (CPMA).  As well as providing information about North American manufacturers, they have been able to give the committee a better understanding of the implications that changes can make.

There is also good cooperation with the Ecological and Toxicological Association of Dye and Pigment Manufacturers and Eurocolour.

So happy anniversary Colour Index, here's to the next 100 years!

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