by Abellio

Bangkok, 3 February 2016

After reading my last post, my wife asked me a very simple but very penetrating question: “But why are jeans blue?”

One can of course be nit-picking and respond that actually not all jeans are blue. This is undoubtedly true but let’s face it, the huge majority of jeans are dyed some shade of blue. Jeans are not called blue jeans for nothing.

One can also give the trivial answer “because blue dye is used”, which rightfully elicits the riposte “Ha-ha, very funny”. But actually, an interesting tale does hang on the dye used, which I learned while preparing the previous post and which I can’t resist recounting here.

We have to go to Europe for an answer to my wife’s question, because it was from there that the denim material used for blue jeans came to America. So what is the history of blue dye in Europe?

I was delighted to learn that the original blue dye of choice in Europe was extracted from woad. For those – I’m sure many – readers who have no idea what woad is, it is a plant native to many parts of Europe from whose leaves indigo dye can be extracted. I throw in a picture here in case any of my readers might wish to go searching for it.

woad plant

Personally, I must admit that I only knew woad as the stuff which Julius Caesar, in his De Bello Gallico, tells us the Britons smeared themselves with: “Omnes vero se Britanni vitro inficiunt, quod caeruleum efficit colorem, atque hoc horridiores sunt in pugna aspectu”, “In truth, all the Britons stain themselves with woad that occasions a bluish colour, and thereby they have a more terrible appearance in battle”. But I prefer the way it is put in that sublime history of Great Britain, “1066 And All That”: “Julius Caesar advanced energetically, throwing his cavalry several thousand paces over the River Flumen; but the Ancient Britons, although all well over military age, painted themselves true blue, or woad, and fought heroically under their dashing queen, Woadicea, as they did later in thin red lines under their good queen, Victoria.” Mel Gibson in Braveheart shows us how it should be done.

mel gibson

Trivia aside, woad was actually economically a very important crop in many parts of Medieval Europe and made some communities very wealthy. In France, for instance, the trade in the dye from woad built many of the more beautiful buildings in Toulouse


while in Germany woad paid for the University of Erfurt, established back in 1389.

erfurt university

The indigo from woad coloured the best of medieval tapestries.

medieval tapestry

In sum, all seemed to be going swimmingly for the woad sector!

But there was a worm in the rose: the same indigo dye, but extracted from the leaves of another plant, in much larger quantities per leaf, in India.


This stuff was already arriving in small and very costly amounts onto Greek, and later Roman, markets, along those same trade routes which I’ve had cause to mention in earlier posts. Because it was so expensive it was used primarily as a pigment in paint and not as a dye of fabrics. The Greeks called it indikon, the Indian dye. The Romans latinized this to indicum, which eventually gave us our indigo. Once the Europeans rounded the Cape of Good Hope and made it safely across the Indian Ocean, they could buy the stuff directly from the producers and cut out all the middle men. Nice packets like this began to arrive in Europe in the hold of European ships.

Indian_indigo_dye_lumpThe price in the European market places duly dropped, woad producers saw their livelihoods threatened, and they resorted to the classic weapons of getting pliant governments to forbid its use (it’s called anti-dumping these days) and putting around rumours that using indigo from India severely affected the quality of the fabric. All to no avail. The higher transportation costs from India were more than offset by the much higher productivity of the Indian plant. Transportation and production costs were then further slashed when the Spaniards started growing the Indian plant in their Latin American colonies and the British in their southern American colonies (Carolina and Georgia), both with slave labour.

Indigo Processing Carolinas

The British then went on to use their early stranglehold on Bengal to create vast indigo estates, turning the local farmers into de-facto slaves in the process, which further reduced costs.

indigo processing bengal

Woad was doomed and disappeared from the scene.

But at this moment of triumph for Asian indigo, there was another worm in the rose, this time in the form of the nascent organic chemical industry. In the early 1800s, when woad was fighting its final rearguard actions against Asian indigo, Europe and North America were starting to adopt town gas to light and later heat homes and businesses. Town gas was produced from coal.

town gas manufacture

Its production also created various very nasty wastes, some of which I have stumbled across in my professional career buried in old gasworks sites. One of these wastes was coal tar, a nasty, gooey, stinking waste which looks like this.

coal tar

Chemists started dabbling with coal tar to see what they could extract from it. The breakthrough occurred in 1856 when a young British chemist by the name of Henry Perkin, while trying to make quinine from coal tar, serendipitously produced a purple dye that he later commercialized under the name mauveine.

mauveineIt must have been so thrilling, almost magic, for Mr. Perkin to extract this beautiful colour from that horrible, nasty black gunk. For sure, in the chemistry lab as a boy I found those moments when the liquid in my test tube turned a beautiful colour to be the most memorable. But perhaps Mr. Perkins only saw the commercial possibilities in this lovely mauve.

In any event, the race was on! Chemists piled in to see what other dyes (and later other organic products) they could make by fiddling around with coal tar. The Germans soon dominated the field, accounting for almost 90% of synthetic dye production at the outbreak of World War I. It took a while for synthetic indigo to be produced, because coal tar didn’t contain a suitable “carbon skeleton”. Finally, in the late 1870s, early 1880s, the German chemist Adolf Baeyer managed to find several routes to synthetic indigo. His Nobel Prize for chemistry in 1905 was partially based on this work. Chemists at the Badische Anilin und Soda-Fabrick (better known to us as BASF) came up with yet another, commercially more viable, route, and BASF marketed its first synthetic indigo in 1897. By the way, just to close the circle, BASF was created in 1865 by one Friedrich Engelhorn, who had established the gasworks for the town of Mannheim in 1861 and saw in Perkin’s discovery of mauveine a way of turning this damned coal tar waste into something useful. As BASF’s name suggests, the company initially focused on aniline-based dyes. This is the original BASF plant at Ludwigshafen in 1866.


Natural indigo was doomed. Synthetic indigo’s better quality, the greater reliability of its supplies, and its lower cost all drove natural indigo off the market, despite the usual attempts, which we’ve seen already with woad, by sympathetic governments to try and block the use of synthetic indigo by fair means or foul. In 1897, the year that synthetic indigo first came onto the market, 19,000 tons of natural indigo were produced. By 1914, this had plummeted to 1,000 tons and the free fall was not over. Asian indigo followed woad-based indigo into oblivion.

At this moment of triumph for synthetic indigo, there lurked yet another worm ready to devour the rose’s heart: other blue synthetic dyes. Indanthrene Blue RS was patented in 1901, Hydron Blue was developed in 1908, and maybe there were others – the world of textile dyes is bewilderingly complex. I’m not quite sure how these various dyes fought it out for the denim market, but in the 1950s BASF and other indigo producers seriously considered promoting other blue dyes for denim because of indigo’s poor fastness properties. This is jargon for meaning that textiles dyed with indigo tend to fade rather easily. What stopped them was the fact that this very property of fading was what was so earnestly desired by the young owners of blue jeans, the product in which indigo was most used. So indigo was saved and the worm crawled off to devour other roses. Because of the popularity of jeans, indigo is in fact king of the heap. It is the textile dye with the highest production volumes in the world, some 30,000 tons a year (when you think that most of it is used to dye jeans and that it only takes 10 grams of indigo to dye one pair of jeans, readers with good mathematical skills will quickly figure out that literally billions of jeans must be made every year).

But after that tour through the world of dyes and its cut-throat competition, I am afraid to say that I still haven’t properly answered my wife’s question: “why are jeans blue?” Why are they not red or green or black or yellow? Well I think we have established why they are blue today: because of indigo’s quirk of fading in interesting patterns. But why did the Amoskeag Mills in New Hampshire, which initially supplied Levi Strauss with his denim, use indigo dye? Despite my best efforts, I have not been able to find a satisfactory answer. I suspect it was because by the 1860s, when the mill started supplying Mr. Strauss with his denim, this particular fabric had “always” been dyed with indigo or woad or some other blue dye. “Always” seems to mean at least since the 16th Century. One article I came across says that it was at this time that blue in the UK became the poor’s colour of choice for their clothing. Judging by the paintings of the Master of the Blue Jeans, it was the colour of choice for the poor in Europe more generally.

master of the blue jeans

Why? I don’t know. I have to assume that cost was a factor, but it could also have been simply a fashion trend.

So I’m afraid that I have failed to answer my wife’s question at the deepest level. But I shall keep an eye out, and maybe one day I will come across the answer and be able to update this post. Any leads will be welcome. In the meantime, I invite my readers to enjoy some blue.

Blue Spectrum


Woad plant: (in

Mel Gibson: (in

Medieval tapestry: (in

Hôtel particulier, Toulouse:’Ass%C3%A9zat,_toulouse_%28panorama%29.jpg

Erfurt University: (in

Indigofera tinctoria: (in

Packet of natural indigo dye:

Indigo processing Carolinas: (in

Indigo processing Bengal: (in

Town gas manufacturing: (in

Coal tar: (in

Mauveine: (in

Old BASF plant: (in

Master of the Blue Jeans painting: (in

Blue spectrum:×455.jpg (in