Among the chapters of Cennino Cennini’s Libro dell’Arte, the Tuscan painter’s handbook for aspiring 15th century artists, you will find the story of an early discovery of ‘a yellow colour called ochre’:

‘I was guided one day by Andrea Cennini, my father, who led me through the territory of Colle di Val d’Elsa, close to the borders of Casole, at the beginning of the forest of the commune of Colle, above a township called Dometaria. And upon reaching a little valley, a very wild steep place, scraping the steep with a spade, I beheld seams of many kinds of colour: ochre, dark and light sinoper, blue, and white…In this place there was also a seam of black colour. And these colours showed up in this earth just the way a wrinkle shows in the face of a man or woman.’

Those wrinkles were some four or five million years old, formed during the Pliocene when Italy was submerged on all sides by heightened sea levels, making it look not so much a boot as a fishing hook. The sedimentation of sands, clays and minerals, rich in iron oxides, would later give this area its fertile soil. As the water receded, it would also leave behind in its wake the bizarre eroded landscape celebrated in Joe Tilson’s eponymous Crete Senesi: the spotted hills with white biancane cones and steep balze cliffsides, their heads washed off by the withdrawing sea to reveal rich mineral deposits beneath; and the calanchi, valleys carved by borri water streams meandering between the hills, which eventually widen out to join the major rivers of the Arbia, Merse, Orcia, and Ombrone along whose banks the ancestral Etruscans settled, Siena’s first founders.

The ochre colours of the Crete Senesi, the clay hills surrounding Siena, Tuscany

Among the creases of colour Cennini picked out with his penknife – ‘I never tried a handsomer, more perfect ochre colour’ – might have been what was termed by later artists Terra di Siena, ‘raw’ Sienna, one of a host of ‘general purpose’ earthen colours that did most of the heavy lifting in the Renaissance artist’s palette, from flesh tones to draperies, horses, buildings, and landscapes.

All earth pigments in the ochre family essentially derive their colour from the presence of iron, in one form or another. Other metal oxides, such as manganese, account for the subtle differences between these relatives: Sienna, yellow ochre’s older and darker brother, named after the city where it was commonly found, owes its maturity to a dash of manganese oxide; add a little more and you enter the saturnine territory of umber, the shades which cloaked Caravaggio and Rembrandt’s darkest paintings in adumbral shadow.

Human beings have been using Sienna to make pictures for as long as we have been producing images. The cave paintings of Lascaux in France, or Altamira in Spain, feature a whole range of these earthen colours, from the brightest of ochres to the darkest of umbers. Ancient man may even have known then that by heating the lighter pigments like Sienna, a darker paint could be achieved; certainly, by the time medieval potters were using the local iron-rich earthenware clays to make their pots, they were well aware of the change in colour wrought by their kilns, when their firings toasted the red clay to a rich, warm brown.

The big change for Sienna likely came in the 13th and 14th centuries when painters began refining that heating process specifically to produce usable powdered pigments. Desiccation of raw Sienna, which was crushed and calcined in a kiln, causes its chemistry to change; between two and three hundred degrees, the iron ore limonite, which gives raw Sienna its wonderful mustard yellow hue, begins to dehydrate and form haematite – essentially, the mineral form of what we would ordinarily call ‘rust’. The higher the heat, the more pronounced the colour change: first to a vibrant, reddish ‘brick’ orange, then darker, richer, and redder still to the hues of ‘burnt’ Sienna. Through this heating process, painters could extract from a single source of pigment a whole earthen palette. Crucially, these were non-toxic, lightfast, quick drying, and – until the 20th century – in ample abundance.

The Abbazia di Monte Oliveto Maggiore, a Benedictine monastery founded in 1313 by Bernardo Tolomei and enlarged in the 15th century

Sienna, raw and burnt, is to be found in almost all Sienese painting of the period, to which Tilson’s Crete Senesi are an explicit, if not recognisable, homage. Artists like Sassetta, Simone Martini, and Giovanni de Paolo used ochre pigments dug from the hills to paint the very same landscape around them, employing Siennas more often for tinting, glazing and in the large, semi-transparent layers of imprimatura than fullbodied brushwork – drawing from one ‘ground’ to make another in paint. In Ambrogio Lorenzetti’s Allegory of Good and Bad Government frescoes in the Palazzo Pubblico, the local seat of the Sienese government, the unforgiving nature of the Crete Senesi was made a landscape fertile for, if not crops, then spiritual and moral instruction: in one panel, under the imagined sway of good governance, farmers collect bountiful harvests and transport their goods to the nearby city; but on the opposite wall, the Crete have become an apocalyptic wasteland, littered with burning ruins and besieged by troops on a scorched earth campaign against the city state.

It was on this very basis that Bernardo Tolomei, a 14th century Sienese philosopher, theologian, and erstwhile knight, withdrew with two fellow noblemen to the Crete ‘badlands’ in pursuit of divine enlightenment and to bring God to its empty, ochre wastes (inspired, perhaps, by Christ’s 40-day temptation in the Judaean wilderness). They lived as hermits in the merciless heat of the Accona Desert, as many miles south east of Siena as Cennini’s home town was north west – a spiritual desert, absent not just of crops and cultivators but of established churches too. Eventually, they would withdraw to the cypress trees of nearby Monte Oliveto Maggiore to found the seat of the Order of the Olivetans, which they ran according to a programme of extreme asceticism. The unaccommodating hills surrounding Monte Oliveto can be seen in the Benedictine frescoes in the monastery by Giovanni Bazzi, known better by his nickname ‘Il Sodoma’ for his supposed taste in young men (Vasari, the famous biographer, with whom Bazzi had something of a contretemps, said the monks knew him as ‘Il Mattaccio’ – the ‘madman’).

In 1348, Siena was hit hard by the plague. Fatefully, it was the same merchant traders who had put the city definitively on the map that were to bring about its downfall when diseased soldiers from the Mongol horde attacked their trade stations in Crimea. The panicked merchants quickly packed up their goods and sailed home, unwittingly bringing with them the plague-carrying fleas on the backs of ship’s rats. Tolomei, despite his important role as chief abbott, joined 81 of his fellow monks in travelling to the city to help care for the afflicted, only to succumb to the disease themselves. Siena, once a thriving hub of Tuscan commerce, lost half its population in a matter of months. It would not recover its preplague numbers for another 700 years.

Before Tolomei had received the necessary papal blessing for his monastery, he is said to have witnessed in prayer a vision of monks in white habits ascending a ladder to heaven, attended by angels and greeted by Jesus and the Virgin Mother. Whether the dream had been real or was concocted to secure the backing of the local Bishop, it makes for a fascinating connection with Joe Tilson, for whom the ladder has been such an important recurring image in his art for its rich symbolism.

Unlike Tolomei, Tilson has never been a religious man – though his attitude toward the craft in his art, the nitty-gritty of cutting, carving, sanding, layering, and print work, has verged on the devout. He shared with the abbott an eremitical dedication to his work, withdrawing in the early 1970s from the busy London scene and working largely in isolation for the rest of his life, whether in the countryside of England or his studios in Italy, which seems now as much his home as anywhere else. But there is something undoubtedly spiritual, theurgic even, in this printed series. The incorporation of direct woodblock printing in the screenprints lend his Crete the feeling of religious ‘tablets’, emphasised by the very thick ink that has been used to print them and which gives them that pronounced raised surface which makes his work so tactile.

Their curvature echoes, in some ways, the arched interior architecture of much Sienese painting, as well as the hills themselves, and the arched wooden panelling used in altarpieces and cabinet paintings. To use another religious term, they seem to me almost like shrouds; as if they were the imprint of the coloured hills themselves, with all their sedimentary and historically symbolic layers. The words and names emblazoned along the bottom of these prints reference the landmarks of the Cretesasso (stone), monaci (monks), and castello (castle) – as well as the less well-known place names that litter the landscape: Murlo, Serre di Rapolano, Montegabbro. Building up the coarse, grained surface of the prints through many screened layers of colour, Tilson made these images in a way that paralleled, in his own words,

‘…the action of time and weather that make the worn, moulded, carved, eroded character of the landscape; sculpted over centuries by rain and wind, plant life and farming.’

‘From the rock split through the slow breakdown of frost and ice comes the topsoil with its insect and plant life, its trees and crops that give that part of Tuscany its form and colours, the dark green rows of cypresses against the silver green of olive trees, the earth turned by the plough reveal colours of the earth pigments of the region used for centuries, and still used by painters.’

‘Those ferric oxides give yellow, gold, brown and red ochres, and raw and burnt Siena.’

Ironically, any Sienna Tilson would have used in the Crete Senesi prints, published in 1995, will have been quite different from the pigments sourced during the Renaissance period. By the early 20th century, the commercial ochre veins around Tuscany had been almost entirely exhausted. Winsor and Newton, the British company famous for inventing aluminium paint tubes, declare on their website that until 1988 they managed to maintain their supplies of raw Sienna from a depleted mine just south of Siena itself. When the mine closed, they bought all remaining stocks of the pigment, which lasted another three years. Other mines had by then been established in Sardinia and Sicily, and further abroad in Germany and the South of France, but with such efficient advances in chemistry and colour science over the last 50 years, most firms – Winsor and Newton included – now use synthetic iron oxides made to demand in labs. Gone is that rich seam of traditional art craft, tying, through this wonderful, natural colour, the work of an artist as contemporary as Tilson with some of the earliest figures in the Western canon. But the hills of Tilson’s suite remain; and the colours of Siena and the Crete Senesi – those life-affirming pigments of prehistory – seem just as vibrant as they must have done some 40,000 years ago.

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