How a classic specialty chemical market works: the synthetic dye industry: Why dyes are the archetypal specialty chemical

1.1 A dye is bought for what it does, not for what it is

Pollak sorts chemicals into three groups. Commodities are single pure substances made in dedicated plants, in large volumes, at low prices, with many uses, and sold on a specification. Fine chemicals are also pure substances sold on specification, but they are made in multipurpose batch plants, usually in volumes under about 1,000 tonnes a year and at prices above about $10/kg. Specialty chemicals are formulations sold on performance: in his phrase, on "what they can do" rather than "what they are". Their buyers mostly sit outside the chemical industry, they carry brand names, and the supplier has to explain how to use them. Pollak lists dyestuffs and pigments among the specialties.

Murmann shows that the dye trade worked this way from its first day. The real cost of a dye to a dyer was not its invoice price. It was the price plus the cost of getting it onto the cloth, set against how long the colour lasted. He lists eight things a buyer judges: the exact shade, brilliance, fastness to rubbing, to washing and to sunlight, the range of colours one dye can give in mixtures, how many fibres it works on, and total cost. Many different molecules that give the same shade are still sold today because each wins on a different mix of these eight.

So a dye is judged in the dyehouse, by trial, not on a certificate of analysis. When Perkin sent his first purple silk to the Perth dyer Robert Pullar in 1856, the reply was that the colour was badly wanted and very valuable, provided it did not make the goods too dear. Performance first, price second: that is the specialty bargain in one letter.

• Pollak (2011) · pdf pp. 26-27
• Murmann (2003) · pdf pp. 48, 263-265, 133, 217
• Murmann (2003) · pdf p. 279 (synthetic indigo launch)
• Pollak (2011) · pdf p. 120

1.2 Thousands of products, each made in small amounts

The second mark of a specialty market is proliferation. By 1912, Hesse counted 921 distinct dyes on sale, made from 270 intermediates, which were in turn made from just nine products taken from coal tar. The same molecule was often sold under several names: as early as 1897 there were about 8,000 trade names. Bayer said it sold 1,800 dyestuffs in 1911, and Hoechst sold some 10,000 trade names by 1913.

Proliferation has a cost, and it can go too far. In 1927-28 the German combine I.G. Farben sold 33,000 dye mixtures under 50,000 brand names. During the Depression it cut the range to 6,000. Today the Colour Index, the standard catalogue run by the dyers' professional societies in Britain and America, lists 9,475 dyes and pigments, but Kent puts the number that sell well at 1,500 to 2,000, with only a handful of real "workhorse" colours in each class.

Why so many? Because each fibre, process and end use needs a different balance of the eight performance tests, and because matching one specified shade can take anywhere from two to a dozen dyes in the same bath. A dye house wants a full palette from one supplier.

The result is small volumes per product. Murmann notes that demand for most single dyes was too small to keep a production line busy. Firms like Bayer therefore ran many dyes and intermediates through the same equipment, scheduling campaigns against forecast orders. Their edge came from scope (making many related products on shared kit) more than from scale (making one product in a huge plant). This only paid if orders were steady, which is why selling mattered so much.

• Murmann (2003) · pdf pp. 49-50, 271-272
• Kent (2012), Ch 13 Dye Application, Manufacture of Dye Intermediates and Dyes · pdf pp. 485-487, 507, 556
• Pollak (2011) · pdf pp. 26, 28

1.3 Matching dye to fibre is where the know-how lies

To see why application knowledge is the heart of the business, look at what a dye must do. Kent describes dyeing from a water bath in four steps. Exhaustion: dye molecules move from the bath to the fibre surface. Diffusion: they move into the looser, amorphous regions inside the fibre. Migration: they spread out until the colour is level. Fixation: they lock on.

How they lock on depends on the fibre's chemistry. Cotton and viscose are cellulose, full of hydroxyl groups that soak up water. Wool and silk are proteins carrying charged amine and acid groups. Polyester takes up only 0.3 to 0.5% moisture and has almost nowhere for a water-soluble dye to grip. So each dye class is defined by how it is applied, not by its chemical family. Acid dyes form ionic bonds with wool and nylon. Basic dyes do the same with acrylic. Direct dyes cling to cotton by weak attractions such as hydrogen bonds. Reactive dyes form a true chemical (covalent) bond with cotton. Vat and sulphur dyes are made soluble by chemical reduction, soaked in, then oxidised back to an insoluble form trapped inside the fibre. Disperse dyes, milled to particles of 1 to 3 microns, dissolve into the polyester itself, forming what chemists call a solid solution.

Each route has costs a dyer feels. Reactive dyes need 200 to 300 g of salt per litre of bath to push them onto cotton, and some dye reacts with water instead of the fibre, wasting colour and tinting the effluent. Before 1914 the craft was harder still: a fast madder red needed more than twenty operations, and the mordant (a metal salt used to bind dye to fibre) changed the colour itself, from red with aluminium to black-violet with iron. A supplier who could solve these problems for a customer held that customer.

• Kent (2012), Ch 13 Dye Application, Manufacture of Dye Intermediates and Dyes · pdf pp. 487-507
• Murmann (2003) · pdf pp. 266-267

See it in the table

Check your understanding

Which statement best captures why dyes are a specialty rather than a commodity?

A dyer wants a very wash-fast colour on cotton leisurewear. Which class does Kent point to, and what is its main drawback?

Why did Bayer run many dyes through the same production lines?