“I had thought, when I set out on my travels – when I first tumbled through that paintbox – that I would somehow find, in the original stories of colours, something pure.”

THE many journeys Finlay undertakes in search of the sources of her artists’ colours mark this history as more than just a text book, rather it is a very visual, very personal, romance. She etches the characters she meets in like a painter herself brushing in a minor person in the crowd – the lonely Afghan lapis miner who replies to her question of what was the best time of his life: when my wife and I were newly wed and locked together like horses.

Like a great war reporter she spends as much time getting permissions and visas to travel to her sources in her great, global quest. She brings an artist’s eye to her expositions along with the histories of colours, now synthetically made but back in the day each had to be ground out in the chemist’s workshop to blend natural minerals and compounds that lie behind the perfect names on pencil shafts like cadmium red or the Persian blue so familiar now from Ming vases and which of course are the mark of all the great art before 1900. Finding colour at all was more than half the job of the apprentices, some concoctions were so extreme like orpiment or Chinese yellow they could be deadly. There was so much arsenic laced into the green and yellow of Napoleon’s bedroom wallpaper, it may even have killed him.

Finlay recites her father taking her to Chartres cathedral and pointing out a piece of blue stained glass as her point of inspiration. And then. “Dutch pink: a fugitive yellow lake made from buckthorn ‘made me swoon with its paradox, I was smitten’”.

So we embark on an odyssey starting in the Vatican archives, then to northern Australia for ochre and the morbid, tangled, shady history of Aboriginal masterpieces – a much more detailed and enlightening exposition than BBC4’s recent attempt – and so on, for each part of the globe has its own secret hue.

Not all is what it might seem, black for example. “In Claude Monet’s Gare Saint-Lazare, the pitch black locomotives in his busy station are actually made up of extremely vivid colours – including bright vermillion red, French ultramarine blue, and emerald green”. Conservationists have revealed he hardly used any black pigment at all.

And then for yellow, we are in Bihar, which may have been the start of painting as we know it, to validate if the source of the famous Indian yellow could really be from the urine of cows fed on mango leaves. That proves a riddle too far. For saffron we start in Kashmir, move up to Tibet, then to La Mancha and back to Saffron Walden where it arrived in the middle ages perhaps in a pilgrim’s hat but died out by 1790, to Iran now the world’s biggest supplier, all the time looking for a delicate flower that only blooms for a day a year, the lowly crocus, and has to be harvested in the morning.

Not only does she have a zeal for her subject and a traveller’s eye for the people she meets but she also has a way with words themselves:

“It is an irony that the old silk roads are the least smooth pathways in the world. In rocky road hierarchies this one was king, and our Soviet jeep had been protesting in a language of clonks and crunches for some hours. Some of the gradients against which the engine would curse in its diesel-fumed Russian were so seemingly impossible that it was a miracle we achieved them each time”.

The history of an everyday craft, a singular human activity, that brings our world, our collective struggles and achievements to light.