A Dyer’s “If”

The pieces of dyed silk had passed an encouraging test. William Henry Perkin sent them to the firm of Pullar in Perth, Scotland, and received a judgement he would remember fifty years later. His discovery could be immensely valuable, the dyers reported, provided it did not make the goods too expensive. Perkin liked the report apart from the “if” with which it began. The condition kept returning as he tried to turn his new purple into a business.

In 1856 he had a colour, a way of producing it in small quantities and evidence that it could stay on silk. He did not yet have a dependable supply of its ingredients, a chemical works or an established method of making it useful to the great cotton trade. The fabric had to justify the expense of everything that happened before it reached the dye bath.

A chemist in the family

Perkin was eighteen. He had entered London’s Royal College of Chemistry at fifteen, studying under August Wilhelm Hofmann, and had become an assistant in Hofmann’s research laboratory. At home in east London he also conducted experiments of his own. His interests had once ranged across carpentry, engines, drawing and oil painting. His father, a builder, had hoped that copying architectural plans might lead his son towards architecture.

Chemistry won. Much later, Perkin recalled a schoolfriend showing him experiments when he was twelve or thirteen. The formation of crystals particularly impressed him. At school, a teacher named Thomas Hall encouraged the interest and made him a lecture assistant. Perkin used the dinner interval to arrange apparatus and prepare demonstrations. Hall also helped persuade his father to let him pursue the subject.

The famous purple emerged during an attempt to make quinine, the medicine used against malaria. Perkin was working with chemicals related to aniline, a substance obtainable through transformations of coal-tar ingredients. The desired medicine did not appear. In experiments with aniline, however, a dark reaction product yielded a purple solution when treated with alcohol. It coloured silk and resisted washing well enough to suggest a useful dye.

The familiar Easter discovery story comes largely through Perkin’s later recollections. The next stage left a more immediate commercial trail. The Science Museum preserves Robert Pullar’s letter acknowledging receipt of dye patterns and offering his experience as a practical dyer. Perkin was seeking the judgement of someone whose work began where a successful laboratory experiment ended.

During the summer, his brother Thomas Dix Perkin helped him make larger experiments and obtain more colouring matter. A patent followed in August 1856. Even applying for it presented a question: could someone under twenty-one receive a patent? In his 1906 account, Perkin remembered obtaining counsel’s opinion that his age did not prevent the grant.

Finding money was harder. Potential backers were reluctant to risk capital on an unfamiliar product. His father supplied the confidence and funds that others withheld. The son who had disappointed an architectural ambition was now asking the family to help build a chemical business. Perkin left Hofmann’s laboratory to pursue it; his teacher disapproved of the decision.

Manufacturing the ingredients

The works opened at Greenford, west of London, in 1857. Coal tar was the beginning of the supply chain, rather than a vat from which purple could simply be drawn. A fraction yielded benzene. Chemical treatment converted that into nitrobenzene, which could then be converted into aniline. Only after those operations could the dye-making reaction begin.

Perkin’s difficulty was therefore larger than finding a vessel for his purple experiment. The starting material itself had been a laboratory substance, rather than an ingredient available in dependable industrial quantities. As he remembered it in 1906, the raw materials were not even being made to a definite quality. Suitable plant had to be devised along with the processes it would perform.

The valuable colour also had to be separated from a mass of less useful material. Calvert’s manual, quoting Perkin’s description of the process, follows several operations after the initial reaction. The dark product was filtered, washed and dried. Treatment with coal-tar naphtha removed resinous material; alcohol then extracted the colouring matter. Removing the alcohol left the dye behind as a substance with a bronze-coloured surface. A purple solution and a dry commercial product did not necessarily look alike.

Each separation meant handling material, using liquids and recovering a small valuable part from the rest. A dye that impressed on a scrap of silk still had to survive those costs. Perkin later dated the supply of mauve for silk dyeing to December 1857, more than a year after the discovery and patent.

Silk was only the beginning

The dyer had another set of problems. A new colouring matter had to spread evenly through the cloth, stay there through washing and produce a shade that a customer wanted. Existing recipes for natural dyes could not simply be assumed to work. Perkin supplied advice as well as colour, helping dyers learn how to use the unfamiliar material.

Silk had given him a fortunate start: the purple attached readily to it. Cotton was much less accommodating. Its fibres did not take up this dye in the same useful way, so an application method had to be developed. Tannic acid helped create an intermediate attachment between fibre and colouring matter. Such a preparation is a mordant: it helps fix a dye that would otherwise have too little hold on the material.

Calvert’s account makes the attraction of tannin concrete. Mixed with a solution of aniline purple, it produced a compound that no longer dissolved in water as the original colouring matter did. The book records work on these combinations by Calvert and colleagues as well as Perkin’s purple. Practical dyeing was becoming an area of competing experiments, with silk, wool and cotton posing different demands.

The new purple was also entering a market that already knew other purples. In Calvert’s telling, its use remained limited until spring 1859, when enthusiasm on the Continent for a colour called French purple helped bring mauve into fashion and enlarged British demand for aniline purple. Fashion supplied customers; chemistry supplied a way to make the colour for them. The fashionable name came from the French word for the mallow flower.

Resistance to washing did not make every mauve textile permanent. Light could still change its appearance. Nor does the present colour of a surviving scrap give an untouched record of its first day in a dyehouse. The specimen in Calvert’s book is evidence of a product being demonstrated to readers, with its own subsequent history on the page.

More than one purple

Consistency began before the dye bath. What nineteenth-century manufacturers called aniline could include closely related substances called toluidines. These were not irrelevant dirt to be removed without consequence. They joined in the reaction and helped determine which coloured compounds formed. Changing the starting mixture could change the resulting purple.

Perkin learned to make bluer and redder shades using material with different amounts of toluidine. Modern analysis has shown how complicated those products were. Mauveine, the name eventually given to the dye, was a mixture of related coloured molecules. A single neat chemical structure cannot stand for everything made and sold under that name.

In 2017, Tânia Cova, Alberto Pais and J. Sérgio Seixas de Melo compared new laboratory preparations with historical museum samples. Varying the proportions of aniline and two forms of toluidine produced markedly different chemical profiles. One preparation closely matched selected historical Perkin samples. That reconstruction gives substance to the manufacturer's problem: repeating the broad outline of the reaction was insufficient if the ingredients differed. It does not recover every batch made at Greenford.

Competitors were developing their own routes. In Manchester, Heinrich Caro worked with Roberts, Dale & Co. on another process for producing purple. Calvert placed a specimen labelled “Dale & Caro’s Purple” just after his discussion of Perkin’s colour, accompanied by a description of their 1860 patent. The reader could compare products while reading how the manufacturers proposed to make them.

Mauve’s strongest fashion did not last indefinitely. Other synthetic colours followed, and Perkin’s firm went on to make other products before he sold the business in 1874. In Calvert’s surviving volume, the two competing purples remain attached to neighbouring pages.